フラッド

テンプレート:Cleanup

小説Halo: The Flood,あるいはHalo Wars第9ステージの The Floodについてお探しですか?

Inferi Redivivus (Flood)
Biological information
Homeworld	不明（銀河系外）
Physical description
Height	多様（宿主による）
Weight	多様（宿主による）
Skin color	多様: 緑、黒、黄褐色（宿主による）　しかし多くの宿主は茶色や緑に変色する
Military and Political information
Distinctions	大幅な生理的および心理的変異、　　また宿主の記憶も取得可能
Equipment	多様（おもに宿主が所持していたもの）: Active Camouflage Elite Personal Energy Shield
Ranks	Gravemind Proto-Gravemind Prophet Form Juggernaut Form (cut) Pure Form Stalker Form Ranged Form Tank Form Infector Form (cut) Transport Form (cut) Stealth Form (cut) Combat Form Carrier Form Infection Form
Affiliation	Inferi genus
Notable Individuals	Gravemind notable infected individuals Captain Keyes Prophet of Regret
Other Nomenclature	"Flood" (Human and Covenant) "Inferi redivivus" (Forerunner) "Parasite" (Covenant)

“フラッドの胞子ひとつで全宇宙が滅びるんだぞ”

— アールタス・ヴァダム

フラッド (英語 The Flood ラテン語 Inferi redivivus、"The dead reincarnated"の意)もしくは The Parasite としてコヴナントの間で知られている。十分な生命力や認知能力をもつ知的生命体を餌食にすることで増殖、成長する、非常に感染力のあるウィルス性細胞生命体である。 およそ931年に及ぶフォアランナー=フラッド戦争の発端となり、フォアランナーが銀河系の生物の多様性を守るための最後の努力として、ヘイロー・アレイを建設した理由も彼らにある。全ての戦力的手段が使い尽くされた後、フォアランナーは紀元前97445年にヘイロー・アレイを作動させ、結果としてフラッドの蔓延を根絶すると同時に、銀河系に存在していたほとんど全ての知的生命体（大部分のフォアランナーも含む）の絶滅を招くこととなった。

フラッドは銀河の最古の保護者（プリカーサー）の原型が損なわれた姿から生じ、他の生物に感染し体と神経系を乗っ取り多様なフォームに変異させてしまうことで繁殖・拡散する。知的生命体に感染することで記憶と知識を取り込み、フラッドは集合的により賢くなる。バイオマスと知能を有するホストが十分にいれば、フラッドはその拡散の速さから止められるものは誰もいなくなる。

全てのフラッドのフォーム（個体）は単一の意識を共有しており、それは新たな知的生命体がホストとして同化されるごとにより賢く洗練されていく。十分多くのホストが感染すると、フラッドの意識は全てのフラッドのフォームを戦略的に操作する自我を持つ知的存在であるグレイブマインドとなる。この集合意識的特性から、フラッドは少数の支配者によって指揮される個体の集合というよりも、ひとつの超知的（transsentient)な巨大な生命体といったほうが正しい。フラッドはグレイブマインドがいない段階では、均等に安定して分布している。彼らは複雑な戦略を組んだり自発的に生殖する能力に欠ける。手近な知的生命体、特に自己認識し内省力のある生命体に攻撃・感染して繁殖することに専念する。この段階のフラッドの感染爆発は野性的段階（Feral Stage）として知られている。この段階のフラッドは犠牲者のバイオマス、カルシウム、神経系などを集めて蓄え、フラッド・ハイブ（巣）やプロト・グレイブマインドの形成につながる。フラッドの集合意識はSFによくあるハイブ・マインドに似ており、フラッドは統一された存在として活動し、他の種に本来的にある個性はない。各フラッドの部位は種の繁栄のために絶え間なく働く。

フラッドは人間やコヴナント（エリートやグラント、ブルートなど）に感染し、彼らをコンバット・フォームを始めとする様々なフォームへと変異させてしまうため、HALOトリロジーにおいては、フラッドは最も多様な形で登場する。感染すると敵を弱体化させると同時に強大になるため、戦闘においては従来になく変化に富む脅威を呈する。天の川銀河では、彼らは生命体の存亡、正確にいえば、生物多様性にとって大きな脅威であるとみなされている。

歴史

起源

“我々の創造への欲求は不変だ；我々は創造せねばならない。しかし我々が創造する者達は二度と強さをもって我々に立ち向かうことはない。創造される者はみな苦しむだろう。全ては苦しみの中に生まれ、終わらない灰色が彼らの土地になる。全ての創造物は失敗と痛みの服を仕立てるだろう。二度と永遠の泉の子孫が創造主に歯向かうことはない。沈黙を聞け。千万年の深い沈黙を。そして今すすり泣きと泣き声を；誕生の泣き声ではない。これが我々がもたらすものだ：若さと希望を押しつぶす大いなる重り。意志はもうない。自由はもうない。苦痛をもたらす死以外新鮮なものはなく良いものはここから生まれない。我々は数百年前にお前達に息と姿を与えた者達の最後の生き残り。我々はお前達が反抗し容赦なく破壊した者達の最後の生き残り。我々は最後のプリカーサー。そして今我々は「レギオン」だ。”

— フォアランナー・フラッド戦争の終盤にカタログに話すグレイブマインド

現在から千万年以上前、プリカーサーとして知られる極めて高度な生物の文明が宇宙で繁栄していた。マントル（銀河の全生物を庇護する責任）を担った彼らは、無数の惑星に生命の種をまき、銀河にある各種の知的生物種を生み出した。プリカーサーの庇護の下、人類とフォアランナーを含むいくつもの知的生命が発展し栄えた。プリカーサーはやがて人類を正当なマントルの継承者に選び、フォアランナーは不適であると判断した。創造主の審判を受け入れること拒んだフォアランナーは、プリカーサーに対して大規模な反乱を起こした。

続く戦争でフォアランナーは殆ど全てのプリカーサーを殲滅する。生き残った（或いはフォアランナーに見逃された）僅かなプリカーサーは静止状態になるか、のちに過去の姿に再構成できる粉へと自分たちを変えた。しかし時間の経過とともに粉には欠陥が生じ、接触した他の生物に病理と生物学的変異をもたらすようになった。この新しい姿（最初期のフラッド）でプリカーサーは彼らの創造物に二度と反抗させないと誓った。 　後に最後のプリカーサーとして知られる大幅に変異した個体は、プリカーサーのステイシスカプセルに封印され銀河の端にある荒廃した小惑星に紀元前9,000,000年ごろ置かれた。 後にプライモーディアルとして知られるこの存在はやがて真実を知ろうとする者にフラッドの本質を明かした。

最初の発生

経過

26世紀に知られているフラッドは、紀元前107,445年以前に古代人類がプリカーサーの粉と接触した後に銀河に初めて出現した。この細かな乾燥した粉は自動化された宇宙船上の数百万のガラス製シリンダーの中に保管されていた。宇宙船は大マゼラン雲の方角から天の川銀河の端へ向かっていた。 しかし数千万年の間にこの物質は徐々に劣化し、船の機能にも障害が出ていた。

これらの船の残骸は人類が初期に進出した銀河間空間の端付近の居住惑星及び無人惑星で太古の人類に発見された。船の中で人類は粉が詰まったカプセルを見つけた。テストの結果、粉は使途不明の不活発な短鎖有機分子ということだった。 人類はこの物質を研究し無害だと見なしたが、下等動物に対して向精神作用があることに気づいた。人類とサンシュウムにペットとして人気だったフェルーという動物に少量が投与され、より従順な行動をもたらした。当時の人類とサンシュウムは知らなかったが、粉はフェルーの遺伝コードを書き換え、行動の改善として発現しながら徐々に遺伝子の他の側面を変えていた。

発生

人類が粉をフェルーに数世紀に渡って投与すると、より忌まわしい変化が現れた。粉を投与されたフェルーは毛皮の増大と肉質の突起物を持ち始め、これを他のフェルーが食べた。しばらくするとフェルーの間に流産と遺伝的奇形が広まり、多くは安楽死させられるか野に放たれた。その後変異したフェルーのそばにいた人間とサンシュームに粉由来病の症状が現れ始めた。心理レベルに影響が出て、感染者は病気のフェルーを食べ始め、投棄された体の部位も病気を媒介した。そして感染者は人食いを始め、犠牲者が人口の多数となるまで非感染者に無理やり食べさてその後彼らを食べた。？（The afflicted then moved on to cannibalism and sacrifice of the uninfected, force-feeding victims until they reached gross proportions and then consuming them.）感染した人間とサンシュウムは他の星系にも病を広げ始め、フラッドの流行の規模を拡大した。

この時点でこれまで主に精神と行動に影響し比較的身体的変化が少なかったフラッド感染は、被害者を様々な形態（フォーム）に変え始めていた。それらは被害者を増やしたり、戦闘を行ったり、有用なバイオマスや他の資源を迅速に食らうようデザインされていた。

拡散と撤退

感染は素早く人類とフォアランナーの支配宙域に広がった。感染した惑星と星系を隔離する試みは失敗し、フラッドはすぐに15星系の何百という惑星に拡散した。 フラッドの拡散と止めようと、人類艦隊はフラッドの感染が検知されたフォアランナー船とフォアランナー惑星を破壊して感染を除去した。人類艦隊司令官のフォーゼンコはフラッドに拡散する時間を与えないために、これらの行動を事前にフォアランナーに警告しなかった。 多くのフォアランナーはフラッドは人類の領土拡張主義的狙いを隠すためのフィクションであると考えた。最終的にフォアランナーは人類の戦術を侵略行為だと解釈し、人類-フォアランナー戦争に突入する。

人類がフラッド感染で著しく弱体化し二面戦争を戦う中、フォアランナーは人類相手の初期の勝利が容易であったことに驚く。しかしどうやら前触れもなくフラッドは人類への攻撃から撤退しはじめた。フォアランナーの船は健全な人類惑星をフラッド蔓延の只中に見つけ、人類はフラッドに対する耐性、免疫ないし治療法を発見したのだと結論付けた。 しかしフラッドへの免疫や治療法は存在しなかった；フラッドは単に人類に感染しないことを選んだのだった。 ウル・ダイダクトは後に、フラッドの意図は人類がフラッドへの解決策を持っていると見せかけることで、フォアランナーによる人類絶滅を防ぐことだったと推測した。

この時点でフォアランナーは初めてフラッドと接触した。パラサイトは多くのフォアランナー艦隊を壊滅させたが、彼らの銀河からの故意の撤退はフォアランナーに有利に働き、銀河周縁部の数千もの惑星のフラッド感染を滅菌することができた。 将来のフラッド再発の懸念を認識していながら、フォアランナーが研究のための無傷のフラッドサンプルを回収するのには困難があった。ウォーリアー・サーヴァントは脅威には相応の注意を持って臨み、感染は遭遇し次第すぐに焼灼したからだ。解析のために回収された残骸から、フォアランナーはフラッドと接触があったAIが修理不可能なほどに汚染されていたのを発見した。これはロジック・プレイグとしてフォアランナーに知られるようになるもので、データに起こるフラッド感染といえる。 フラッドの無傷のサンプルはフェルー、人間、サンシュウムの中には見つからなかった。彼らは組織的に感染の痕跡を発端の宇宙船も含み全て破壊していたからだ。 残存していたフラッドはすべて感染した船で銀河の外に逃げたと考えられ、 フラッドはその後約1万年間姿を現さなかった。

人類はフラッドが撤退し始めると勢力を幾分取り戻し、戦争の終盤までフォアランナーに抵抗した。フラッドに対する軍事行動で資源がすり減っており、ダイダクト率いるフォアランナー軍が有利な位置を固めると彼らは持ちこたえることができなかった。 徐々に星系を失い、人類は首都であるチャラム・ハッコーにまで退却した。そこで彼らは敗北する。終戦の後フォアランナーは人類を退化させ故郷である地球に追放し、銀河から人類の功績の痕跡を全て消した。

中間期

証拠の不足から、ほとんどのフォアランナーはフラッドの存在ないし本質に気づいていなかった。フラッド到来前から初期にかけて多くのフォアランナーはフラッドは単に人類の侵略的拡張のための言い訳であるとみなした。 しかし少数のフォアランナー高官は脅威を十分に認知しており、密かにフラッド再来に備えて対策を構築しはじめた。これは大規模な政争につながり、ビルダー達が超兵器群であるヘイロー・アレイの建造を提案する中、ダイダクト率いるウォーリアーサーヴァント達は惑星規模の要塞であるシールドワールドから精緻な軍事行動を実行するより従来型の戦略を推した。ダイダクトはやがてビルダーに敗北しウォーリアー・サーヴァント階級は主流から外れ、艦隊と軍隊は解散させられるかビルダーの管理下の置かれた。これはフラッド再来時の備えの不十分さにつながり、大きな過ちだったといえる。

フラッドによる知的生命根絶の脅威とヘイロー使用の展望を認識したライフワーカー階級は「保存策」を実行し始めた。これはフラッドを研究しつつ銀河の生物種を集めヘイロー関連施設に保存するもので、主に銀河外のアークという施設が使われた。

フォアランナー=フラッド戦争

フラッドは、惑星シーワードでフォアランナーたちが初めて遭遇したときに、銀河系の中で現実的な脅威として再び現れた。当初、フォアランナーたちはこの寄生生命体がもたらす潜在的な脅威を著しく過小評価しており、実際の戦争よりも疾病対策に適した戦術を用いていた。感染が広がり始めた頃には、フラッドはより致命的で知的な敵となっていた。当初、フラッドは初歩的な戦略能力すら持ち合わせていなかったが、パラサイトはすぐにバイオマスを蓄積し、フラッド種の集合的な知性を体現するフラッド形態であるグレイブマインドを生み出した。グレイブマインドはフラッドの大群を調整し、テレパシーのようにコントロールできる広大な範囲内にあるすべてのフラッド形態を使ってフォアランナーの艦隊を攻撃することができた。

フラッドの一般的な戦術は、非武装の民間船を大量に利用して惑星防衛群に侵入し、フォアランナーの軌道艦隊を回避して、惑星とその住民に感染するというものであった。膨大な数のフラッドフォームが、フォアランナーの地上部隊を圧倒した。数十億の形態が惑星攻撃に投入され、すべてのフォアランナーがフラッドの宿主となる危険にさらされた。これらの戦術はLP656-38eやDM-3-1123bを含む数多くの世界へのフラッドの攻撃で実証された。絶望的な状況の中、フォアランナー艦隊は汚染された世界への全面的な軌道爆撃を行ったが、大きな犠牲を払った。海軍の守備隊が砲撃を開始できなかった場所では、フォアランナーの主要な人口集中地区で局所的な大量破壊兵器が作動し、事実上の集団自殺となったが、感染の拡大を食い止めることができた。

その後、従来の海軍戦術では、フラッドの感染を食い止めることができないことを悟ったフォアランナーたちは、より極端な手段でフラッドを打ち破ることに望みを託すことにした。フォアランナーは当初、フラッドと戦い封じ込めるためにセンチネルを配備していたが、その直後、フォアランナー艦隊司令部は「早期的な恒星崩壊」を考えた。これは、海軍を使って星を超新星に送り込み、惑星系を飲み込んでフラッド感染の可能性を防ぎ、星系に存在するすべてのフラッドを破壊するというものである。 フォアランナーのさらなる失敗として、プライモーディアルとの長期にわたる対話が、フォアランナーの防衛を担当するコンテンダー級AIのメンディカント・バイアスを刺激し、フラッドのペスト・ロジックに屈して、その膨大な資源をフォアランナーに向けてしまった。プライモーディアルの肉体は破壊されたが、その意識はフラッドのニューラルネットワークに転送され、フラッドにかつてない知能とパワーを与えてしまった。

最後の10年

フラッドは指数関数的に成長し、フォアランナーのとの戦争に勝利するためではなく、フォアランナーを感染させる目的でシステムからシステムへと広がっていった。フラッドがさらに広がると、惑星全体が感染し、これらの惑星サイズのキー・マインドは、処理能力においてフォアランナーのAIを容易に凌駕することができた。 ペスト・ロジックは目的のために様々な形態に変化し、フォアランナーが考案したすべての防御策を突破し、最終的にはAIとデータ・ネットワークの間で拡散した。これらの惑星サイズのキー・マインドは、処理能力においてフォアランナーのAIを容易に凌駕することができた。論理的疫病は目的のために形態を変化させ、フォアランナーが考案したすべてのセキュリティを突破し、最終的にはAIとデータ・ネットワークの間で拡散した。フォアランナーは戦闘においてAIの自動化に大きく依存していたため、これはフラッドに対するフォアランナーの軍事的努力を大きく妨げた。さらに、戦争末期になると、フラッドがプリカーサーの技術を操作できることが明らかになり、スターロードに代表されるプリカーサーの巨大構造物を利用し、以前は不活性だった構造物を活用してフォアランナーの惑星や海軍を攻撃するようになったのである。この能力は、フラッドがプリカーサーとして生まれたことによるもので、プリカーサーに変身した彼らは、Neural physicsを利用してプリカーサーの人工物を作動させることができたのである。また、高レベルのキー・マインド・ノードの拡散により、フラッドはプリカーサーのNeural physicsに基づく超光速移動を利用することが可能となり、フォアランナーのスリップスペース移動を妨げていた。

ヘイローの起動

Main Article: 大粛清

フォアランナーはフラッドの発生を抑えるために様々な手段を講じたが、いずれも失敗に終わった。最終手段として、7つのリング状の巨大構造物「ヘイロー・アレイ」を超兵器として使用し、銀河系から生物を一掃することを決断した。フラッドは寄生生物であり、その生存は宿主の存在と直結しているため、宿主となる可能性のあるものをすべて排除すれば、寄生虫は成長・拡散できなくなり、最終的には餓死してしまうと考えたのである。さらに、マスター・ビルダーがシャルム・ハコールでヘイローのテストを行った結果、ヘイロー効果によって神経構造が破壊されることが判明した。つまり、すべての動物種、フラッド、プリカーサーの人工物が死滅する可能性があったのである。 この決定は、政治的な争いや内戦にまで発展したが、あらゆる対策を尽くした後、フォアランナーは紀元前97,445年にヘイローを起動させた。

7つのヘイロー・アレイが起動された結果、生き残ったフラッドの封じ込めに成功し、やがて絶滅した。生き残った唯一の標本は、ヘイロー施設や特定のシールドワールド、スレッショルド・ガス鉱山など、最先端でセキュリティの高いフォアランナーの研究施設に収められた。また、神経エネルギーのみで構成されたプリカーサーの人工物や構造物も破壊された。 銀河中の多くの知的生命体（人類を含む）は、箱舟に乗ったフォアランナーによって銀河の外に安全に移され、ヘイロー・アレイの起動から逃れることができた。

エトラン・ハーバレージでのアウトブレイク

Main Article: Battle of the Etran Harborage

フォアランナーとフラッドの戦争が終結してから数千年後、コヴナントに捕らえられたアンダース教授の信号を追って、人類の船UNSCスピリット・オブ・ファイアがアルカディアを飛び立った。辿り着いたのは未知の惑星で、そこはたまたまフォアランナーのシールドワールドだった。この惑星では封じ込め対策が大失敗し、メガストラクチャーの表面全体がフラッドのバイオマスで窒息していた。船のレーダーに映った未知の敵対者の存在を調査するため、地上部隊が投入された。フォージ軍曹と数名の海兵隊員は、コヴナント軍をかわした後、フラッドの攻撃を受けた。

フラッドを撃退したUNSC軍は、アンダースの信号が出ていたと思われる場所に射撃基地を設置した。人類はその信号を、いくつかのフラッドのコロニーに取り付けられた巨大なプロト・グレイブマインドにたどり着いた。プロト・グレイブマインドはアンダースの信号を複製し、人間に感染させてエトラン・ハーバレージの外に広めようとしていたのである。洪水のコロニーを殺すとプロト・グレイブマインドが弱まることがわかり、SPARTAN-IIレッドチームがファイアベースの協力を得てプロト・グレイブマインドを破壊した。

これに対してフラッドは、スピリット・オブ・ファイアのアルファ、ブラボー、チャーリーの各小隊が船に戻らないように大規模な攻撃を仕掛けてきた。大規模なフラッドの抵抗にもかかわらず、スピリット・オブ・ファイアの部隊は、ファイアベースがフラッドに制圧される前に小隊を救出することができた。

グレイブマインドが死んだ後、スマートAIのセリーナはアンダースの信号を再取得し、内部のシールド世界につながるドッキングポートがある海の下へと導いた。スピリット・オブ・ファイア号の降下中、船の外面にはフラッドが蔓延していた。スピリット・オブ・ファイアの乗組員は、センチネルとAIが制御する「浄化リング」の助けを借りて船を浄化し、シールドワールドへと進んだ。

その中でUNSCは、表面の惑星ほどではないが、シールドワールドの内部にもフラッドが侵入していることを発見した。フォージはアンダースを救出する際に、3体のフラッド感染体からアンダースを救い、その後の任務でもフラッド軍とのトラブルに遭遇したが、外部の惑星で見られたような大規模なものではなかった。

コヴナントがエトラン・ハーバレージのフォアランナー・ソジャーナー級ドレッドノートの艦隊を手に入れるのを防ぐため、スピリット・オブ・ファイアのショウ・フジカワ・トランスライト・エンジンのリアクターを使って、シールドワールドの人工星を超新星に誘導する計画が立てられた。この計画は成功し、エトラン・ハーバーは破壊された。この爆発により、惑星上のフラッドはコヴナント軍とフォアランナーの艦隊とともに消滅した。

短期的な再発

Main Article: Outbreak on the UNSC Spirit of Fire

エトラン港での出来事から6年後の2537年1月1日、UNSCスピリット・オブ・ファイアでは、船内に隠れていたポッド感染者によってフラッドが発生した。ジェローム-092は、エレン・アンダース教授の助けを借りて、感染した乗組員を強制的に駆除し、スピリット・オブ・ファイアと残された乗組員の生存を確保したのである。スピリット・オブ・ファイアに残留していたフラッドの痕跡はすべて駆除された。

フラッドの復活

Main Article: Battle of Installation 04

Jacob Keyes and his Marine squad are overwhelmed by the Flood during their expedition into a Flood containment facility.

“The only way to stop the Flood is to starve them to death.”

— Cortana to John 117 and 343 Guilty Spark.

ヘイロー・アレイの最初の発射により、銀河に逃れていたフラッドは餓死したが、フラッドの標本はインスタレーション04や様々なフォアランナーの研究施設など、銀河中の施設に保存された。これが大きな間違いであったことは、アレイの発射から数千年後、人類とコヴナントの双方が、放棄されたヘイロー・リングの1つを偶然発見したことで証明されている。UNSCのAIコルタナは「オータム」に搭乗し、コヴナントの追手から逃れるためにスリップスペースを「ブラインド」でジャンプした（実際にはシグマ・オクタヌスIVで発見されたフォアランナーの遺物から座標を翻訳して使用した）。その結果、Installation 04にたどり着き、そこに保管されていたフラッドを発見した。ジェイコブ・キーズ船長が操縦するPillar of Autumnがヘイロー・リングに墜落した後、生き残ったクルーは身を潜めた。

一方、追いかけてきたコヴナントのクルーザー（「Truth and Reconciliation」など）は地表に地上軍を集結させ、やがてリングの沼地にある地下のフォアランナー・フラッド封じ込め施設を発見した。この施設は安全性が高いため、コヴナントはその本質や目的を知らずに、要塞化された作戦基地や武器・弾薬の保管場所として利用していた。

ある時、封じ込め装置の故障かコヴナント側の不手際で、施設内のステイシス・チェンバーに捕らえられていたフラッド・フォームが解放され、内部のコヴナント軍を攻撃したのである。フラッドの能力について初歩的な知識を持っていたコヴナントは、直ちに施設を閉鎖し、生き残った人員を避難させた。

キーズたちはそのことを知らずに施設の奥深くへと進み、ついに未開封のフラッド格納庫の1つを発見した。何かの武器の隠し場所だと思って扉を開けると、中にいたポッド感染者に襲われて感染してしまった。艦長の失踪を知らされたジョン117は、エコー419でキース大尉の最後に確認された居場所に向かい、施設内に入ったが、大尉を含む救出に当たった海兵隊員のほとんどがフラッドに感染していたことを知った。

これらの出来事により、UNSCはフラッドの存在を知ることになった。損失の多い戦争の中で、これは人類にとってまたとない厳しい事実であった。

Assault

The Flood engages both UNSC and Covenant in their drive to escape Installation 04.

フラッドが脱出した後、インストレーション04のコヴナント軍はフラッドの攻撃に圧倒された。コヴナントは車両や航空支援を利用して戦線を維持することができたが、アンゴイやキグヤーなどの弱いコヴナント兵のほとんどはフラッドに簡単に屈し、残った少数のサンヘイリも数で勝てず、感染してしまったという。アルファ・ベース付近でコヴナントと交戦していたODST部隊がフラッドに待ち伏せされ、大きな犠牲を出したのだ。しかし、攻撃してきたコンバットフォームの1人、ウォレス・A・ジェンキンス海兵隊員（PFC Wallace A. Jenkins）は、何世紀にもわたる冬眠で感染力が鈍った弱った高齢のポッド感染者に感染し、ジェンキンスのコンバットフォームへの変身は不完全なものとなった。ジェンキンスは、心の中に蔓延するフラッドに抵抗することができた。言葉を発することができず、肉体的には壊滅状態であったが、アントニオ・シルバ少佐との尋問の際に手振りでフラッドを裏切り、フラッドが現在の作戦基地の地下にある一連の地下墓地からUNSC基地を襲撃する計画であることをUNSC海兵隊大隊に伝えたのである。この情報を受けて、UNSCは地下墓地の確保に動き、フラッドの再攻撃を阻止した。

この間、リングのセンチネルはフラッドを効果的に封じ込めることができず、その結果、コヴナントとUNSCは大きな損害を被った。フラッドはかつてコヴナントが所有していたリングの地域を占領したが、コヴナントとフラッドの部隊はリングの巨大な氷の平原で戦争を続けた。コヴナントはシェイドの固定式プラズマ・タレットと車両・空中支援の恩恵を受けていたが、フラッドはUNSCとコヴナントの武器を奪い、そのために数的優位に立っていた。

フラッドに捕らえられたUNSC隊員の一人、ジェイコブ・キーズ大尉は、UNSC海軍の優秀な海軍戦略家であった。彼が感染したとき、フラッドは彼がフラッドにとって特に有用な知識を持っていることを察知した。キーズは、人類発祥の地であり重要な拠点である地球の位置を知っており、フラッドにとっては同化の可能性が非常に高い惑星であった。キーズは戦闘体になるのではなく、他の少なくとも4人の犠牲者とともに、巨大で肥大化したプロト・グレイブマインドとして、フラッドが乗っ取ったコヴナントのCCS級戦艦「Truth and Reconciliation」に組み込まれた。原始的なグレイヴマインドに組み込まれている間に、フラッドの知性は彼の心を探り、地球の位置を記憶していたのである。キーズ船長は、ジョン-117が到着するまでの間、自分の名前、階級、シリアルナンバーなどのコマンド・ニューラル・インターフェイスで得られる情報に常にアクセスすることで、地球に関する情報を隠すことに成功した。しかし、彼の到着は遅すぎた。キーズはすでに原始的なグレイブマインドに飲み込まれて死んでいたのである。ジョン・117はその時、キャプテンのCNIトランスポンダを手に入れるために、キーズの頭蓋骨に穴を開けざるを得なかった。

Truth and Reconciliationは、コヴナントの特殊作戦部隊とフラッドの間で大きな争点となった。フラッドはコヴナントの乗組員と守備隊のほとんどを壊滅させ、孤立した抵抗勢力だけを残していたが、そのほとんどが少数の怯えたアンゴイと数人のサンヘイリであった。しかし、「Truth and Reconciliation」の下、一連の岩の多い峡谷では、コヴナントの力ははるかに強く、アンゴイ、キグヤー、ムガレクゴロによって増強された多数のサンヘイリがフラッドを撃退していた。しかし、インストレーション04の作戦を担当するコヴナントのマスター評議会は、フラッドの存在に恐怖を感じていた。CCS級バトルクルーザーは、以前のUNSC Pillar of Autumnとの宇宙戦で損傷を受けたため、少なくとも2日間は下腹部とプラズマ輸送管の修理を待つために地上に留まっていたのだ。フラッドがバトルクルーザーに搭乗していることが判明した後、コヴナント軍首脳部は特別作戦攻撃隊を「Truth and Reconciliation」に派遣し、直ちに応急修理を開始して宇宙への離陸に備え、フラッドを無力化することにした。しかし、その努力もむなしく、最終的にはフラッドに奪還されてしまったのである。

その後、リング上に残っていたUNSC海兵隊は、フラッドが保有する「Truth and Reconciliation」への攻撃を行い、迅速な攻撃で巡洋艦に搭載されていたほとんどのフラッド形態を無力化することに成功し、リングから脱出して地球に帰還するために、急遽完了した応急修理で戦闘艦の離陸準備を行った。しかし、フラッドに感染した船が地球に向かうには多大なリスクがあり、もしフラッドのキャリアフォームが1体でも乗っていれば、フラッドの指数関数的な寄生能力のため、UNSCのAIウェルズリーによれば「地球は落ちるかもしれない」とのことだった。海兵隊のメリッサ・マッケイ中尉は命令に反して、フラッドの形態が残っているものを含めて軍艦を破壊し、感染したジェンキンスを含む数百人のUNSC軍人を殺害したが、地球とおそらく数十億人の命をフラッドから救ったのである。

Defeat

The Pillar of Autumn - exploding, with its fusion reactor becoming destabilized, destroying both the ship and the ringworld, to prevent the Installation from being fired and taking the threat of the Flood with it.

The Flood were interested in seizing space-capable vessels, in the hope of spreading the infection away from Installation 04 and across other systems; they attacked the UNSC Pillar of Autumn and cruiser Truth and Reconciliation for this reason. After the UNSC cruiser's crash-landing onto the ring, and after engaging over fifteen enemy warships previously to landing, it had been taken by the Covenant, although a UNSC strike team had managed to temporarily retake the bridge. On the third and final day of the Battle of Installation 04, however, the Covenant were able to gain control of the crashed warship while one of many Covenant patrols around the exterior of the Autumn was ambushed by the Flood and infected; upon the patrol's return to the vessel, the Covenant garrison was attacked by the infected Elite combat forms of the patrol group. The combat forms were able to scatter before they could all be destroyed, and a steady trickle of Flood continued to enter the Pillar of Autumn through vents and openings in the hull, waging a tedious guerrilla battle against the Covenant security force on board. On another occasion, the Flood attempted to enter through cargo containers but were foiled due to the quick thinking of the Unggoy Yayap.

Eventually, a force of Sentinels came on board, overwhelming the dwindling Covenant forces as the Flood began to attack the warship in full force, in the end almost completely obliterating the Covenant presence, and severely limiting the Sentinels' numbers on board. Despite their best efforts and enormous numbers, the Flood, Covenant, and Sentinels were unable to stop John-117 from detonating the wrecked warship's reactors, and escaping in a Longsword interceptor. The resulting thermonuclear detonation from the destabilized fusion reactor cores severed a portion of the ring world, ultimately destroying it and its capability to annihilate all sentient life, and simultaneously killed all remaining Flood on Installation 04, along with any other life forms that were still present on the ring.

Outbreak on the Mona Lisa

Main Article: Skirmish on Mona Lisa

After the destruction of Installation 04, in October, 2552, a human prison ship, the Mona Lisa, arrived in the Soell system and managed to retrieve surviving specimens of the Flood for study from the remains of Installation 04. They began to test the parasite on both human and Covenant prisoners, unaware of its lethality. Soon, the infection broke quarantine and the ship was infested by the Flood. The Flood absorbed the crew and prisoners, then began to build a proto-Gravemind in its engineering section. The infestation ended when Sergeant Zhao Heng Lopez and her marines from the UNSC Red Horse were sent to investigate the ship after retrieving a survivor from the ship. The Flood absorbed many of her marines, leaving her and a single Sangheili to fight for a single-occupant escape pod. The outbreak was most likely contained when the Red Horse destroyed the Mona Lisa using a Shiva-class nuclear missile.

Threshold gas mine

Main Article: Battle of the Threshold gas mine

Dormant Flood in receptacles housed in the gas mine.

The Flood were also kept in a Forerunner-constructed gas mining facility suspended over Threshold, within at least one of the three arms of the station. A small Covenant special forces strike team, led by Special Operations Commander Rtas 'Vadumee and the Arbiter Thel 'Vadamee, were dispatched by the High Prophets to silence Sesa 'Refumee, the leader of a heretic faction, who was stationed within the mine. The heretics released the dormant Flood within the station in an attempt to halt the progress of the Spec-Ops team through the station.

The heretics' plan backfired, as the Flood killed and infected many of their forces while failing to stop the Arbiter and his team. The Flood broke out of the station's arm and spread to the central core of the station, where they overwhelmed the heretics stationed there. Eventually, even the station's Sentinel forces were completely obliterated as the Flood spread to the upper levels of the station. The Flood were unable to escape the station, however, as the Arbiter managed to sever the cable attaching it to the Forerunner support structure far above, sending the gas mine plummeting to Threshold's liquid hydrogen core.

Battle of Installation 05

The Flood were in search of the Activation Index, a device which would deprive UNSC and Covenant forces from the privilege of assured destruction of the parasite.

Main Article: Battle of Installation 05

On Installation 05, the Flood had been in a continual battle with the Sentinels after the initial firing of the Halos 100,000 years prior. Again, a secure facility was breached and a Flood form managed to escape, thus beginning the battle with Sentinels. While the infestation had been contained to a quarantine zone established outside the Installation's Library, and presumably was severely weakened due to a lack of fresh host bodies, the Flood had managed to keep a Gravemind form alive deep within the cavernous tunnels of the ring. With the arrival of the Covenant and pursuing UNSC forces, the Flood was able to grow its forces considerably and redouble its assault on the Installation's security forces.

The Flood, despite a significant vehicular and infantry presence in the Quarantine Zone surrounding the Library, were unable to deny access to the Covenant and the UNSC. Miranda Keyes managed to slip the In Amber Clad through the Forerunner Enforcer patrols, while the Covenant launched a ground attack, led by Thel 'Vadamee and involving a small team of Spec Ops Elites, using two anti-gravity gondolas to get to the index while attempting to control the gondolas and keep it from slipping into Flood or Sentinel hands. Later, the In Amber Clad was captured by the Flood.

Attack on High Charity

John-117, who had arrived with Keyes and Johnson, met Thel 'Vadamee in the clutches of the Gravemind, the central controlling intelligence of the Flood hive, created from the combined intellect of tens of thousands of assimilated corpses. The Gravemind attempted to convince Thel 'Vadamee, against his own beliefs, and through the use of the captured Monitor, 2401 Penitent Tangent, and the semi-revived and consumed Prophet of Regret to not activate the ring. Even though Thel 'Vadamee was still unswayed, although in question of his religion, the Gravemind sent him and John-117 to search for the Activation Index to keep the Covenant from "turning" the "key," transporting John-117 to High Charity, and Thel 'Vadamee to Delta Halo's Control Room.

Taking advantage of the distraction that John-117's presence caused, as well as the ensuing Great Schism, the Gravemind took the opportunity to deliver itself, as well as a multitude of Flood underlings, onto In Amber Clad and then "jumped" the UNSC ship directly inside High Charity, whereupon it immediately crashed into the city's superstructure to deliver its infectious cargo, while a wave of Flood-controlled Pelican dropships delivered Flood forms all over the city. The ill-equipped and distracted populace was no match for the Flood onslaught, and the Covenant Holy City was quickly overrun, with even the Prophet of Mercy falling victim to a Pod infector.

The Flood soon spread to every district, and Flood spores began to infiltrate and overload the ventilation systems within High Charity; the whole city was becoming terra-formed into a gigantic Flood hive. The Gravemind regularly rebutted the words of comfort the Prophet of Truth regularly delivered to the city’s population over the comm system, to sadistically instill more panic and unease. John-117, having successfully stayed in front of the wave of Flood running rampant in the streets, stowed away on the Forerunner Dreadnought that was leading the Prophet of Truth's fleet to Earth. Cortana, who had to stay behind to detonate In Amber Clad's engines should the situation arise and Installation 05 be fired, was left in the clutches of the Gravemind, who could potentially learn all possible human knowledge from her, including the entire knowledge directly received from Forerunner systems aboard Installation 04.

Earth, the Ark, and the Flood's defeat

A UNSC Marine being infected by the Flood.

Main Article: Battle of Voi

At the conclusion of the Battle of Voi, with the Prophet of Truth activating the Portal and the Jiralhanae fleet escaping to the Ark, a Flood-infested Covenant cruiser appeared out of Slipspace, having penetrated the Elites' blockade of High Charity and crash landed into the city of Voi in an effort to spread. In order to prevent the Flood from escaping and infecting the entire planet, Miranda Keyes ordered John-117 to detonate the cruiser's reactors and search the ship for Cortana, causing the city of Voi to be destroyed and the Flood there eliminated. As John-117 and Thel 'Vadam fought their way to the ship, the Sangheili assault carrier Shadow of Intent under the command of Rtas 'Vadum arrived and deployed Sangheili task force to aid UNSC marines. John-117, with the help of the Sangheili, was able to battle through the Flood forces, including the newly encountered Flood Pure Forms to reach the crashed cruiser where he found a message from Cortana. Upon this discovery, 343 Guilty Spark arrived pledging his assistance to the Reclaimers. With the Flood spreading, John-117 boarded a Phantom while the Sangheili went on to glass the infected areas. The remaining Sangheili forces, fulfilling their mission of removing the Flood from Earth, retreated back to the Sangheili carrier, the Shadow of Intent, along with Cortana's message and Guilty Spark.

With the assistance of 343 Guilty Spark, Cortana's painful message was repaired, revealing a solution to the Flood menace on the Ark. To Lord Hood's disapproval, Miranda Keyes led UNSC forces allied with Thel 'Vadam's and Rtas 'Vadum's Sangheili forces through the Portal.

On the Ark, while the Sangheili and human forces were attempting to infiltrate Forerunner shield control centers and lower the shield surrounding the Ark's citadel, the infested High Charity made a Slipspace jump and smashed into the Ark, releasing the Flood onto the super-structure and causing an infestation on the newly built replacement ring for the previously-destroyed Installation 04. The Gravemind then made a brief alliance with the Master Chief and the Arbiter, Thel 'Vadamee, in order to stop the Prophet of Truth from activating the Halo Array. Once Truth was dead, however, the Gravemind treacherously ordered the Flood to turn against the two heroes. The Chief and the Arbiter escaped, however, with some assistance from the Sentinels, who were able to help subdue the Flood with ease.

John-117 stepping in Flood biomass as he enters the Flood infested High Charity.

After retrieving Cortana from the derelict High Charity, John-117 was able to kill all Flood present on the Ark and replacement Installation 08 by first destroying High Charity's plasma reactors, causing a massive explosion and the destruction of the wrecked super-city, then activating the unfinished Halo using the Index Cortana retained from the first Halo, but not before 343 Guilty Spark realized their intentions of destroying his second ring installation, and went rampant, aiming to kill the Master Chief and destroy Cortana before their actions could be completed. 343 Guilty Spark was not successful in preventing the Chief and Cortana from activating Installation 08 and was thus destroyed. Sergeant Avery Junior Johnson was also killed during this brief, but intense battle due to taking a direct pulse beam to the chest from 343 Guilty Spark. The ring's activation was successful and killed most of the Flood forms along with the Gravemind. However, in its presumed final moments, the Gravemind addressed the Master Chief and the Arbiter telepathically, warning them that their victory would only slow—not stop—the Flood.

Aftermath

Even though the Gravemind was destroyed, and all Flood on the Ark apparently eradicated, it is probable that the Flood still exists on the other Halo rings (excluding Installation 05 which was sterilized by Sangheili forces) or any other remaining Forerunner installations. Even though Path Kethona was sterilized by Omega Halo near the end of the Flood war, given the Flood's extragalactic origin, it is possible that more pockets of Flood exist outside the galaxy - or more disturbingly, that other, more distant galaxies may have fallen to the Flood. This may explain why the Forerunners preserved some Flood for research on the Halo rings instead of destroying them all, since the Flood would return sooner or later, and it would be better to fight a researched enemy, and try and find and exploit some weakness, rather than a foreign one. At least for the moment, the Flood are seemingly defeated.

Though the UNSC kept the Flood's existence concealed from the general population, it did make preparations for the possibility of the Flood's return. The new Spartan branch was designed as a first line of defense against the Flood, and teams were deployed to quarantine any areas of potential Flood contamination during the UNSC's initial forays onto Halo Installation 03, though it is unclear whether the parasite was actually encountered. The SPARTAN-IV complement of the UNSC Infinity run simulations depicting the possible return of the Flood. This is realized through both War Games exercises and the interactive TACSIM.

Nightmare on the Ark

A Flood tank form overwhelms a Warthog.

Main Article: Second Ark Conflict

In mid 2559 the Banished and the crew of the UNSC Spirit of Fire fought for control over Installation 00. After the loss of the Enduring Conviction, the Jiralhanae brothers Pavium and Voridus were tasked with securing salvage outside the ruins of High Charity. Atriox, aware of the Flood's potential presence within the city, warned them to not enter High Charity. Voridus, however, believed the parasite was propaganda from the Prophets. As such, he broke through the containment shield with a Scarab, inadvertently releasing the Flood (the parasite having survived the firing of Installation 08 and the ignition of High Charity's backup reactors in some capacity), and starting a second Flood infestation on the Ark. After the destruction of a Proto-Gravemind on the verge of becoming a Gravemind, the Flood was defeated and contained once more.

Flood forms

The Flood is composed of a variety of specialized forms, each filling a different role in combat. The most basic Flood forms are the infection forms, which come in various types and infect hosts by hijacking their bodies and nervous systems. Infected hosts then undergo a rapid series of transformations, becoming lethal combat forms. Combat forms are used to subdue and secure additional hosts for infection, and once they have outlived their usefulness as warriors, they transform into carrier forms, spreading the Flood by spreading more infection forms.

Once the Flood has amassed enough bodies to create a Gravemind, it is capable of generating "pure" forms, which are created solely from assimilated nutrients and biomass. The pure forms observed during the outbreak in late 2552 were able to spontaneously mutate between three configurations: Stalker, Tank and Ranged forms, although in practice the true extent of their mutability is impossible to effectively catalog.

The Flood at this point relegate the combat forms to defensive purposes or as additions to the biomass, calcium, and nervous system reserves of the Flood hive, and rely increasingly on the pure forms as their primary instrument of infantry force. However, in order for the pure forms to fully replace the combat forms, the pure Flood population must be large enough and in a state of equilibrium, which is in a constant state of flux depending on Flood gains and losses. Because of this, it is common for the combat forms to serve alongside the pure forms, in addition to the infection and carrier forms, as the acquisition of hosts and technology would likely outstrip the speed in which the Flood can generate pure forms.

Spores

Main Article: Flood spore

Spores are minuscule airborne Flood forms that serve to spread infection and suffocate potential hosts who inhale them.

Infection forms

Infection forms are the most basic category of the Flood parasite, consisting of several varieties of both ground- and airborne Flood forms.

Tadpoles

Flood tadpoles in a tank.

Main Article: Flood tadpole

Pod infectors undergo a tadpole phase of development before growing into full physical maturity.

Pod infectors

Main Article: Pod infector

These are among the most basic of Flood forms. They are tasked with seeking hosts, then infect them that mainly on the ground.

Seeder infectors

A Seeder infector.

Main Article: Seeder infector

These are airborne forms of Pod infectors that mainly tasked with infecting airborne creatures.

Pure forms

Main Article: Pure form

These forms are the natural Flood species, developed without a host.

Infester Forms

An Infester form.

Main Article: Flood infester form

These forms attack and infect vehicles.

Carrier forms

Main Article: Carrier form

These forms incubate Pod infectors, and release them upon death.

Spawner Forms

A Flood Spawner.

Main Article: Flood spawner form

These forms can produce a variety of Flood forms on the move.

Flood burster

A Flood Burster.

Main Article: Flood burster

These forms can produce a variety of Flood forms and release them once its internal pressure has reached a certain point.

Combat forms

Main Article: Combat form

Once a host of any organic/sentient species has been infected, they can develop into a combat form.

Key minds

Main Article: Key mind

Key minds are nodes for the Flood's collective consciousness, ranging from mobile coordinating forms to compound minds spanning entire planets.

Juggernaut

Main Article: Flood Juggernaut

The Flood Juggernaut is a large Flood command form directed by a seething mass of infection forms linked to multiple hosts.

Abomination

An Abomination.

Main Article: Abomination

The Abomination is a mobile, low-level key mind form capable of combat that coordinates the Flood on a local scale.

Proto-Gravemind

Main Article: Proto-Gravemind

A biomass of hosts, for the purpose of utilizing their minds to form a collective intelligence. A Proto-Gravemind can grow into a Gravemind given enough time and host bodies.

Gravemind

Main Article: Gravemind

This ultimate Flood form serves as the coordinating hive mind of the Flood. While they vary in size and complexity, at their height Graveminds can engulf entire worlds.

Biology

A wall covered in heavy Flood biomass: evidence of advanced infestation.

A Flood spore.

The Flood is an anomaly in all known biology; their mode of growth and reproduction would make them incompatible with any natural ecosystem. They are extremely adaptive, and transform hosts to suit the species' current needs.

Capable of surviving extreme environments ranging from -75 to +53 degrees Celsius and even underwater, the Flood can withstand the varied environments of all known inhabited planets. However, the Flood seem to thrive the most in moist and humid areas; it is thought that the extremely cold artificial weather patterns near certain important areas of the Halo rings are intended to hinder the Flood. In order to give themselves ideal living conditions, the Flood will transform the environment to better suit their needs, altering the atmosphere and covering solid surfaces with Flood biomass.

All Flood biomatter is made of a unique, undifferentiated "Super Cell", which relays information and coordinates the cellular assembly like conventional neural cells. It is also capable of flexing and moving in coordination with other cells, and can be arranged to mimic any bodily organ that is required for the Flood's use. This combination of traits has caused some to refer to it as "thinking muscle."

The Flood Super Cell physically resembles both neuron and glial cells in structure, with a central cell body and many tendril-like, branching structures.

Infection

Flood Super Cells performing cell division inside of a host.

The Pod infector; the primary method administered towards the infection of an organism.

In order to reproduce and grow in biomass, the Flood needs to infect and assimilate other life-forms. While capable of infecting nearly any organism, the Flood shows a strong preference for sentient life-forms, as assimilating their cerebral tissue allows the Flood to increase its overall intelligence.

The first stage of a Flood outbreak is typically initiated by contact with Flood spores or even more reduced forms of Flood biomatter, should no extant Flood forms be present. Once a basic infestation has been established, Flood infection is typically carried out by Pod infectors, which are some of the most complex forms that can be generated from Flood biomass during the Feral Stage. Upon sighting a host, a Pod infector will leap for the most accessible area of the victim's torso; if the target is an armed human or other bipedal species, this is typically the left side of the chest below the neck, as most combatants will expose this area while shouldering their weapon. Upon contact, the Pod infector will rasp away at clothing and flesh until it has burrowed into the chest cavity, mortally wounding them. As the host dies, the Pod infector extends tentacles that tap into the victim's spinal cord or other nerve center, forcing a "match" with the nerve signals previously produced by the host's living brain.

To begin the physiological conversion of a host, the Pod infector injects encapsulated Flood Super Cells into the body. As it does so, the form analyzes the entire genetic code of its host, allowing the Flood to determine the most effective use of the victim. Simultaneously, the inserted Flood cells capture and break down the host body's cells into organic raw material, which is then absorbed and assimilated into the attacking Flood cells.

The Flood infection then uses the absorbed biomass to create new masses of Flood Super Cells. As the Flood continues to use the resources of the host body, particularly its calcium reserves, the parasite's own cells build upon and augment the framework of the host to produce one of a variety of Feral-Stage Flood forms. This entire process, from the initial kill to total control over a fully mutated host body, takes only a matter of seconds.

The infection process is not limited to living hosts; organisms that are already deceased are also susceptible to infection. As long as the host has not decomposed to the point where the body and nervous system have completely deteriorated, the Pod infector can infect and convert the host.

The Flood infection utilizes the host's biological content as the fuel for its work, which is consumed and employed at prodigious speeds. From the beginning until the end of this complex, multi-step process, the Pod infector keeps the body "alive" by chemically isolating the host's dying brain, preventing the signals of brain death from reaching the rest of the body and causing it to shut down, which is an essential part of the parasite's mission of consuming and converting the host organism.

While the Pod infectors are an effective and economical means of delivering infection, particularly against armored targets, the Flood can infect hosts through other means. Flood spores, if inhaled, can transform a host into a combat form. This is the Flood's primary means of infection when an outbreak reaches a certain point: Flood spores will be deployed into a local biosphere in copious quantities, instantly overwhelming any unprotected biological targets. Flood conversion may also be initiated through contact with lacerated tissue, making any Flood form a potential vector for infection. Even the most basic form of Flood genetic material is virulent; once inserted into a host, it will mutate the host's DNA over the course of generations until it is capable of forming its own Flood super cells. When infected by these mechanisms, host organisms tend to mutate at a more restrained level that maintains the structure and form of the infected life form, albeit with a significant number of haphazardly placed tendrils, claws, and minor organs, such as sensory stalks.

Neurological

Pod infectors selectively target species that possess sentient intelligence and are of sufficient biomass, and can infest intact or lightly wounded dead bodies. As a host organism is killed by the initial attack, Pod infectors use tendrils that pierce the skin of the host and find their way to the spinal cord. They then synchronize with the host's nervous system and gain control of their body, replacing its now-absent consciousness with the ravenous and voracious psyche of the Flood. Any useful information present within the memory centers of the host's brain, such as battle strategies and technical knowledge, is retained for use by the Flood. Despite this lingering of certain memories, no trace of the original mind remains; only a simplistic and primal urge to assimilate other species drives the organism after infection. However, the entirety of the host's mental content is seemingly absorbed and added to the whole, as the Gravemind has shown to be able to simulate its victims' consciousnesses within itself.

In isolated cases, such as when the Flood seek very specific information from an individual's mind, they utilize an alternate method of infestation that does not subdue the host's consciousness immediately despite mutating their physical form; this allows the Flood to "burrow" into the host's mind, eventually giving them access to the entire scope of the host's memories. This has only been specifically seen when the Flood sought information from Captain Jacob Keyes, such as the location of Earth, or a starship that would free them from Installation 04. In addition, if the Pod infector that initiates assimilation is extremely aged or damaged somehow, the host may remain alive and conscious; Private Wallace Jenkins suffered such a fate, remaining alive and fully aware of his situation despite the mutation of his form, even exhibiting limited control over his body at times when the Flood instincts were dormant.

When the Flood have amassed enough sentient hosts to form a Gravemind, then their behavior becomes far more coordinated, and the Flood collective becomes much more deadly as a result. The Gravemind may also speak directly through combat forms and pure forms under its control.

Physiological

While baseline neurological assimilation is the same regardless of host species, the Flood infection process includes physiological transformations, which vary depending on the host and the Flood's present need for specialized combatants.

Upon being infected, higher-level species capable of combat are typically transformed into combat forms. The host's physiology is completely "rewritten" during the infection process: organ-based systems are corrupted, organ-specific functions are decentralized, and body cavities are decayed, making hitbox-selective incapacitation impossible and brute force incapacitation difficult. Due to the lack of a central nervous system, decapitation will neither stop or slow a combat form.

Furthermore, munitions with high speed and penetration, such as sniper rifle rounds, are usually ineffective against combat forms. Picking off selective areas of a combat form leads to no wide-scale physiological impediments, and the projectile will punch through the decayed flesh rapidly, exiting through the other side of the combat form without dealing any major damage.

To facilitate melee combat, combat forms generate tentacles and claw-like structures, which protrude from the host's arms. Generally, a single arm develops into a clawed appendage, while the other retains the capacity to manipulate objects, such as firearms. The rapid growth of these structures tends to push aside and break apart the host's hands and forearms.

Combat forms can strike with devastating force, move with tremendous speed and agility, and jump to great heights, displaying physical abilities far beyond those of the host organism while it was alive.

The price for these formidable abilities is that the required metabolism is so rapid and extreme that the host organism's corpse is rapidly broken down by the parasite. This is dramatically demonstrated by the rapid decomposition and disintegration of an infected life-form, which will eventually become a stunted, bloated, mobile generator and incubator for more Pod infectors, which is commonly known as a carrier form.

Pod infectors and pure forms sense their surroundings using specialized tentacles, which are tipped with red ganglia. Exactly how these organs work is unknown; they may provide visual or chemical information, or perhaps a combination of both. In combat forms, these tentacles typically protrude from the chest cavity where the Pod infector is housed; in pure forms, they are located on the front of the "head" segment.

The described changes occur when the Flood has still yet to overwhelm any meaningful resistance in a given locale. When this has been accomplished, available organisms will no longer be used to create purpose-built combat forms but are instead used to create a Gravemind or simply broken down and processed into biomass for a Flood hive.

Metaphysical and technological

“The Flood changes everything. Not just flesh. Space itself is infected. That's the power the Precursors once had... isn't it?”

— The Ur-Didact to the IsoDidact.

Although the Flood is biological on the most basic level, as an outbreak advances, it becomes a highly powerful self-replicating swarm which will seek to harness any mechanism — philosophical, ideological or technological — to perpetuate itself and its goals. These aspects were most prominently demonstrated during the two major outbreaks in the Forerunner era, particularly the Forerunner-Flood war.

The Flood's most notable meta-biological aspect is the logic plague, an abstract infection carried along information transmission and exchange, typically used to subvert AIs. Mechanisms used to perpetuate this infection range from subtle philosophical persuasion through mutual conversation to more predatory techniques, such as swarming AI networks with a self-replicating information infestation with the ability to convert most machine intelligences near-instantaneously. In the later days of the Forerunner-Flood war, the Flood was able to spread the logic plague through any of its biological forms or infected ancillas.

During its war with the Forerunners, after accumulating sufficient intellectual capacity and processing power in the form of several planetary Key Minds, the Flood gained the ability to manipulate neural physics, which served as the foundation of Precursor technology. This enabled it to control the Precursors' formerly dormant structures—most prominently star roads—and use them as weapons against the Forerunners, as well as manipulate space-time to become incompatible with Forerunner slipspace travel. On a more abstract level, the Flood's connection to neural physics caused the Forerunners to experience the very space-time around them as being increasingly hostile. Upon the development of a Gravemind, the Flood becomes capable of what can be described as telepathy among its hosts; given the Flood's origins, this ability may be related to neural physics.

The Flood is able to use any technology it has assimilated, often to a superior degree than the original creators of said technology due to its vast base of knowledge and intellect, as evidenced by its ability to transition the UNSC frigate In Amber Clad into High Charity with a precision slipspace jump normally unheard of with human ships. Similarly, it was capable of tapping into Installation 05's teleportation grid and utilizing it with great accuracy.

Developmental stages

A Flood infestation goes through four distinct developmental stages:

1. During the Feral stage, the Flood are at their simplest form: they communicate via pheromones and have the instinct to harvest enough calcium to establish a viable Gravemind.
2. The Flood become truly dangerous during the Coordinated stage: at this point, they are controlled by the Gravemind that was created in the first stage.
3. In the Interstellar stage, the Flood take control of space-faring technology which they use to consume the local star system. Subsequently, they spread throughout the galaxy to infect more hosts.
4. The Transgalactic stage is a theoretical stage in which the Flood utilizes all captured technology to depart to uninfected galaxies to further replicate.

テンプレート:Flood

Countermeasures

A Marine being attacked by a Pod infector.

Small-scale

There is no confirmed way to effectively stop a Flood infection once Flood Super Cells have entered a host. The only exception is too rare and factually suspect to be considered viable: the human disease "Boren's Syndrome", a neurological condition where radiological exposure causes electrical anomalies in the host nervous system, allegedly renders the host immune to infection while living. The neural frequencies of the host are "scrambled", apparently without negative consequences to the host. However, during Flood infection, the Pod infector is unable to tap into the host's nervous system, rendering it incapable of proceeding to large-scale physiological mutation. An interesting side effect of this failed infection is that Flood DNA and cells appear to be harmlessly integrated into the host's body. This seems to provide the host with increased regenerative capabilities, although this has not been independently verified. While Boren's syndrome left untreated may render the victim immune to the Flood, leaving it untreated almost always equates to death within a couple of years. There is said to be a "one in a billion" chance that research into the disease could produce a cure. However, the accuracy of this information remains highly dubious, as most of it is simply a hypothesis devised by Dr. Halsey to explain how Avery J. Johnson survived Flood infection. Johnson's "Boren's Syndrome" was actually a story invented to cover his past in the ORION Project: his symptoms were side-effects of his experimental enhancements, not a neurological disease.

While the Forerunners could not find a cure for Flood infection, the Composer was designed to eliminate its effects by extracting a Flood victim's consciousness into digital form and then re-inserting it in an artificially-constructed body devoid of infection. However, the Forerunners never perfected this process and any imprinted bodies died soon after, due to the Flood somehow resuming the infection in the new body. The Forerunners attempted to use various means to slow down this process, including a specially designed harness of mesh and wires, which would apparently counteract the infection. The victim would retain most or all of their mental faculties and self-control, although their body would continue to be mutated by the Flood. This countermeasure was only temporary, however, and the victim would eventually either decay and die or be fully subsumed by the Flood. Several Forerunners on Installation 07 were subjected to this countermeasure.

Although initially used to treat those with small-scale Flood infection already present, the Composer was eventually used by the Ur-Didact to convert his Prometheans, as well as a large number of humans, into AI constructs for his war machines, in an effort to combat the Flood more effectively and without risk of infection.

Large-scale

Since the Flood are a parasitic life form, they depend on other organisms for survival. Thus, the most effective way to stop a large-scale infestation is to take away their food sources. The Forerunners first attempted this by bombing large population centers and destroying inhabited star systems via supernovae, but this was seen as one of their last resorts and as such was performed too late in the war to make much difference. The last resort was the use of the Halo Array, which destroyed all sentient life in the galaxy and starved the Flood into extinction. However, the Forerunners' plan included some measures to preserve sentient life and return them to their home planets, allowing the Flood's "food source" to persist. Unfortunately, at the same time, specimens of Flood spore cells were kept for analysis on the Halo installations, allowing the threat of the Flood to be merely forestalled and not eradicated.

Environmental stimuli seem to have an effect on Flood metabolism. In the event of a Flood outbreak, Halo installations create a quarantine zone around the affected area, inside which the ambient temperature is drastically lowered. At least one Flood research facility used low temperatures to keep its specimens inactive and dormant as it studied them. At least one of the Halo installations' Control Rooms was located in a snowy environment, possibly to hinder escaped Flood in their attempts to reach it.

The Flood are also vulnerable to temperatures on the other end of the spectrum. Plasma weapons will easily burn through Flood tissue; the Forerunners incorporated directed-energy weapons into their Sentinels, indicating that they had determined high-enthalpy energy weapons to be the best 'basic countermeasure' available to fight the Flood. Known examples of Forerunner personal weaponry appear to be geared toward the disintegration of organic matter, also reflecting the Flood's vulnerability to extremely high temperatures. The UNSC has taken advantage of this weakness as well, making heavy use of flamethrowers in their engagements with the Flood.

When engaging heavily entrenched Flood structures such as colonies and Cocooned bases, orbital bombardment is usually a preferred method of elimination as direct attacks can be extremely costly.

The "cure"

During the human-Forerunner wars, humanity (who at the time was a technologically advanced, spacefaring race) believed they had discovered another way to defeat the Flood. Using genetic engineering, a third of the human population was altered to carry a set of specially designed genes. This group of humans was then allowed to be infected by the Flood. Once the genes were exposed to Flood DNA, they triggered a cascade of cell destruction that spread throughout all Flood biomatter. The majority of the Flood died off as a result, although they would return in full force ten thousand years later. All information regarding this "cure" was destroyed by the humans as a final act of revenge against the Forerunners, leaving them unprepared for the second Flood strike.

In reality, while humanity's efforts indeed produced the intended result and repulsed the Flood threat, it was later revealed by the Primordial that the Flood retreated by its own initiative, as humanity was not yet to be "tested" by the Flood. As such, humanity's survival was in fact due to the Flood's deliberate decision not to infect human populations, as the Precursors had determined to use the Flood to punish the Forerunners first.

After the Flood began to ravage the Forerunners' ecumene, Forerunner scientists led by Master Builder Faber tried in vain to extract information on the cure from humans' ancestral memories, imprinted as part of their geas by the Librarian, unaware that the cure never really existed.

Combat behavior

The Flood emphasizes numerical superiority in engagements.

The Flood's combat strategy is simple: they throw themselves at potential hosts in huge numbers and with any and all weapons available. The parasite seeks to saturate its opponents with an excess of noise so thoroughly it impedes the enemy's ability to process information and prevents them from organizing a meaningful resistance. The Flood exhibits this behavior on all levels, from its physical swarm tactics in both ground and space to its corruption of data networks and, once an outbreak has progressed far enough, space-time itself.

Flood tactics are based primarily on asymmetrical warfare, using various different forms to kill and infect enemy forces. Infection forms swarm across the battlefield in waves, reanimating any corpses and victims they can find, while combat forms attack and kill any living hosts in sight. Pure forms, if present, provide support to combat forms in a number of ways: Stalker forms move to strategic positions and mutate into either Tank or Ranged forms, which can destroy enemy vehicles or fortifications or provide suppressing fire from afar.

The Flood have a strong preference for close-range combat: combat forms possess extremely powerful melee capabilities due to their specialized claws and tentacles, and are capable of bringing a suit of MJOLNIR armor's energy shields to half strength with a single strike. Exploding carrier forms cause tremendous damage at close range, with the added benefit of spewing Pod infector in the immediate vicinity of enemies. Pod infectors are capable of attacking only at point-blank ranges, exploding in damaging bursts when meeting an opponent's personal energy shields or instantly grabbing hold of an unshielded enemy organism and infecting it.

Typical Flood combat behavior: ravenously targeting the nearest enemy, with Pod infectors running ahead of combat and carrier forms.

Combat forms can also use firearms, and have been seen clutching them in one of their hands (regardless of whether it is one-handed or two-handed). However, combat forms are very inaccurate when using ranged weaponry; it is believed that the neurological and physical effects of Flood infection significantly decrease accuracy.

The Flood collectively learn any information contained within the minds of their sentient hosts. For example, during the ill-fated raid on the Infinite Succor, after even one Sangheili was assimilated, all the Flood could open any doors and access any system on the ship immediately afterward, demonstrating the Flood's ability to share collective knowledge across their species. Furthermore, when the Flood assimilated the Prophet legate, the Minister of Etiology, the Flood reflected the high-level knowledge of the Legate through its individual organisms to Special Operations Commander Rtas 'Vadumee, mocking him with the words, "the Forerunner could not defeat us...what chance you?". The Flood, however, reflect unusual knowledge in the individual psychologies of its individual species in processes facilitating increased infestation: The Flood were sighted gathering bodies in the corners of the Covenant ship Truth and Reconciliation, perhaps making it easier for infection forms to find hosts to reanimate. The Flood were also gathering body parts for a new proto-Gravemind aboard the Infinite Succor.

Flood combat forms have been sighted crudely operating Type-32 Ghosts, Warthogs, Wraiths, and Scorpions in ground operations, although with slow deliberation and clumsy driving and accuracy. The assimilated crewmen of the UNSC frigate In Amber Clad were also able to initiate a Slipspace micro-jump for the frigate and perform rudimentary maneuvering of the In Amber Clad, navigating the frigate from the atmosphere of Delta Halo to High Charity and then crashing the vessel into a tower, releasing Pelican dropships to rain down upon the Covenant capital.

While one of the Flood's main strengths lies in the decentralization of its compound mind and ability to be reborn from even the most carefully reduced remnant, it is nonetheless known to develop and assume a certain "core" Gravemind as an embodiment for its strategic intelligence. The Forerunners observed that the Flood exhibits a seemingly instinctive tendency to recoil and concentrate all of its otherwise distributed assets around this core when threatened on a large scale. A threat to the Flood's existence major enough to prompt such action was the imminent firing of the Halos, at which point the Flood gathered all of its available assets and launched an attack on the Ark.

The Flood is very effective on a psychological level, as its parasitic nature and gruesome appearance alone are a source of horror for most of its enemies and thus serve as powerful demoralizers. It is not uncommon for survivors of Flood encounters to be severely traumatized, often to the point of delirium, after witnessing their comrades get infected or being subsequently forced to kill said infected individuals.

Notable victims

Private Wallace A. Jenkins Private Riley Captain Jacob Keyes Private Manuel Mendoza Lance Corporal Eugene Yate Cranker Gersten Orlav

Prophet of Mercy Prophet of Regret Prophet of Truth Minister of Etiology Sub-Commander Bero 'Kusovai Bok Mendicant Bias 2401 Penitent Tangent

Gameplay

Main Article: The Flood/Gameplay

Changes from Halo: Combat Evolved to Halo 2

• In addition to making low growls, the Flood make screeches and roars, which were not present in the first game.
• Their skin is more textured due to the improved graphics engine, giving the Flood a more realistic and necrotic look. The faces of the human forms are also more readily recognizable.
• If a combat form has both arms shot off, it will walk slowly then explode, releasing the Pod infector that was controlling it. This eliminated the Flood Buddy glitch.
• Rather than having to "gather bodies," the Flood can seemingly infect hosts over the course of a few minutes or even a few seconds, once again possibly due to the presence of the Gravemind, eliminating the need to gather bodies to form one.
• Rather than corpses reanimating themselves, a Pod infector will enter the body, then reanimate it, even if the form was just eliminated.
• If the player is attacked by a Pod infector while their shields are down, the character will die instantly. In Halo: Combat Evolved, it would simply take a bar of health away.
• Some combat forms derived from Elites still have functional energy shields. However, they never possess active camouflage, as some in Halo: Combat Evolved's final level did.
• Flood combat forms can use vehicles, albeit clumsily and are also able to board the player's vehicle; they will then proceed to melee the player character and pull them from the vehicle.
• Melee attacks do little to no damage against the Flood in Halo: Combat Evolved. They deal a bit more damage in Halo 2.
• The Flood prefer to stay back and fire on the player rather than rush him. This could be because of the presence of the Gravemind, though, from a gameplay perspective, it is due to improved artificial intelligence.
• In Halo: Combat Evolved a combat form would walk slowly when shooting at the player. When losing the arm that shoots, it would charge the player character. In Halo 2, combat forms either use a melee attack or shoot at the player in these situations.
• If a player is wielding an energy sword or shotgun, a combat form may retreat. They will not do this if a player is wielding other weapons.
• Unlike in Halo: Combat Evolved, shooting one Pod infector will not result in the rest of the swarm exploding with it. However, Pod infectors are encountered in proportionally smaller numbers in comparison to Halo: Combat Evolved.
• Pod infectors appear noticeably less textured and detailed than in Halo: Combat Evolved.
• Flood Combat Forms do not "feign death" anymore.
• Splattering become more difficult as the Flood can use the vehicle momentum to hijack the vehicle.

Changes from Halo 2 to Halo 3

• Brutes may now be infected and transformed into combat forms.
• Melee attacks and plasma weapons were nearly useless against the Flood in Halo: Combat Evolved and Halo 2, but now can be used effectively against the Flood. The Flood are much more vulnerable to ballistic weapons, as well.
• Pod infectors can mutate humans and unshielded Elites and Brutes into combat forms within seconds (as seen, grotesquely, during Floodgate).
• Pure forms are introduced.
• Combat forms wield weapons far less frequently than in Halo: Combat Evolved and Halo 2.
• Carrier forms release significantly more Pod infectors when they explode. The explosion does not push the player away much as in Halo: Combat Evolved and Halo 2. In addition, carrier forms are significantly more difficult to kill with projectile weapons, but they are easily destroyed by plasma weapons.
• Running over Pod infectors while driving a vehicle can result loss of steering and possibly overturning of the vehicle. Any Pod infectors that are hit by the vehicle will not pop.
• Flood combat forms can no longer commandeer vehicles, like they could in Halo 2.
• Sticking a carrier form with a Plasma Grenade or Spike Grenade will kill both the carrier form and the pod infectors it carries. This is also true of a supercombine explosion

Changes from Halo 3 to Halo Wars

Significant changes to the Flood's general existence were necessary due to the change of genre from first-person shooter to real-time strategy game. These are as follows.

• Many new forms, such as bomber forms, were created for Halo Wars to expand the "roster" of Flood units. The official explanation is that these forms were created from creatures indigenous to Shield 0459.
• Pod infectors no longer push back the heads of their Elite victims; it appears as though the Flood actually use the hosts' heads. In addition, combat forms have more tentacles than before; they resemble spikes rather than flexible appendages.
• Grunts and Jackals can be converted to combat forms.
• Pod infectors do not explode when they are shot in the cinematics, instead 'deflating' like punctured balloons, though they still explode in gameplay.
• Carrier forms do not always explode upon death.
• The instant-kill feature is retained, Hero Units that do not have shields will be instantly downed regardless any remaining HP on them.

Changes from Halo Wars to Halo Wars 2

• The Flood now has a Super Unit, The Abomination.
• New forms are introduced, such as Flood spawner forms, which can spawn Flood forms on the move and can spawn counter units.
• The Flood now only infects the Squad Leader(Either Jiralhanae or Sangheili depending on the Leader) in a Grunt Infantry unit, while the rest are killed. Marine units are entirely infected, retaining Halo Wars infection traits for humans.
• Pod infectors can now be killed more effectively with units that deal splash damage.
• The Flood can now infest and commandeer vehicles that are still operational except Super Units and mechanical units (Mainly Sentinels).
  • Seeder infector, a new variety of Infection Form that is able to infect air units, is introduced.
  • Pod Infestor is introduced and specialized in infecting the vehicles.
• Turret defenses have had their effectiveness reduced against Pod infectors, even those equipped with anti-infantry upgrades.
• The infection process affects all units. If the Pod Infector units doesn't match it's victim (For example, Pod Infestor attacks infantry unit is not match for infection), it will be destroyed or killed. If match, the infection process can be started.
  • Any infected units will revert their health back to 100% once the infection process has been completed.
  • Infection process can be started once a unit is dying (Red Health).
• New structures for barricades are introduced.
• Pod infector squad size increased 3 to 4 times.
• Biohazard sign appears everytime a units is getting infected.

Production notes

テンプレート:Linkbox

The earliest extant concept art of the Flood, by Robert McLees.

Miscellaneous

• The Flood's AI routines in Halo: Combat Evolved were originally intended to be "every bit as complicated as the Covenant", but full implementation was prevented by time constraints.

References

• The name of the Flood is a reference to the biblical story of the Great Flood. Some of the parasite's history mirrors the story, in which God destroyed all life except for that which was carried by Noah's ark.
• The Flood bear a strong visual resemblance to an enemy cut from Marathon 2, the “fungal zombie.” These were to be the result of a bioweapon invented in the final days of the ancient S'pht and reused by Robert Blake's forces on Lh'owon, designed specifically to target Pfhor. Both the fungal zombies and Flood were principally designed by Robert McLees.
• The Flood were inspired by Christopher Rowley's The Vang.
• An alien virus named "The Flood" appeared in a 2009 special episode of the British science fiction television show Doctor Who. Although like its Halo counterpart, it is hinted to be intelligent, and is extremely virulent, transforming its victims physically, the Flood found on Mars literally uses water to transmit itself. The previous episode, also a special, involved the alien planet "San Helios", a name very similar to Halo's Sanghelios.

List of appearances

Halo: Combat Evolved (First appearance) Halo: The Flood Adjunct (Mentioned only) Halo: First Strike Halo 2 Conversations from the Universe (Mentioned only) Halo Graphic Novel Breaking Quarantine The Last Voyage of the Infinite Succor Halo: Ghosts of Onyx Iris Halo 3 Bestiarum Halo: Contact Harvest (Mentioned only) Halo Wars Halo Legends Origins Halo: Evolutions - Essential Tales of the Halo Universe Human Weakness Soma the Painter The Mona Lisa Wages of Sin Halo: Blood Line (Mentioned only) Halo: Reach Data pads テンプレート:Im

Halo: Cryptum Halo: Glasslands (Mentioned only) Halo: Combat Evolved Anniversary Terminals Halo: Primordium Halo 4 Terminals Halo: Silentium Halo: Rebirth (Mentioned only) Halo: Spartan Assault Halo: Escalation Halo: Mortal Dictata (Mentioned only) Halo: Broken Circle (Mentioned only) Halo: Nightfall (Mentioned only) Halo 2: Anniversary Terminals Halo: New Blood (Mentioned only) Halo: Hunters in the Dark (Mentioned only) Halo: Last Light (Mentioned only) Halo 5: Guardians (Mentioned only) Halo: Shadow of Intent (Mentioned only) Halo Mythos Halo: Fractures Defender of the Storm Halo: Tales from Slipspace Something Has Happened Halo Wars 2 Halo: Envoy (Mentioned only) Halo: Fireteam Raven Halo: Renegades (Mentioned only)

Sources

テンプレート:Flood テンプレート:Organizations