United Nations Space Command Defense Force

The United Nations Space Command Defense Force (UNSC Defense Force or UNSCDF for short) is the defensive military force of the United Nations Space Command, consisting of the Air Force, Army, Marine Corps, and Navy, which serve as a joint air, land, and space force.

Interplanetary War
The UNSC Defense Force was likely created during the Interplanetary War, once the structure of the UNSC was formed. As a result of the UNSC's complex command structure, the UNSCDF is assigned to serve a ground and aerial defense force. Before it was destroyed by the Covenant in 2552, Reach served as the dominant UNSCDF military base, with numerous shipyards and docking stations, barracks and training facilities, and twenty Orbital Defense Platforms. It is likely that the UNSCDF has elements stationed on other planets within the Solar System, besides Earth. Mars was one such colony that housed UNSCDF elements.

Human-Covenant War
During the Human-Covenant War, the UNSCDF was called into action on Earth, and possibly Harvest as well. The most notable military engagement the UNSCDF has participated in is the Battle of Earth. The UNSCDF, as a planetary defense force combining all branches of the UNSC, has multiple command bases situated in various regions of Earth such as Crow's Nest in Kenya.

Organization
As the main military branch of the UNSC, the UNSCDF is comprised of three autonomous of semi-autonomous branches, each with different functions and methods, but all unified under one command, and tasked with the protection of humanity, and the protection and recapture of human-occupied colonies. Control is exercised through regional CENTCOMs, which have authority over certain areas of space.

So far, the best-known members of the UNSCDF seem to be the Navy and Marine Corps, likely due to the space-oriented nature of 26th Century warfare. While also a part of the UNSCDF, the Army and Air Force are less well known.

Unified Earth Government and Colonial Administration Authority
 * United Nations Space Command
 * UNSC Security Committee
 * UNSC Security Council
 * United Nations Space Command Defense Force
 * High Command (HIGHCOM)
 * Administrative
 * Personnel Command (PERSCOM)
 * Navigation Command
 * Unified Ground Command (UNICOM)
 * Colonial Military Administration
 * UNSC Astrophysics
 * UNSC Medical Corps (MEDCORPS)
 * UNSC Engineering Corps (ENGCORP)
 * UNSC Test and Evaluation Corps
 * UNSC Ordnance Committee
 * Uniformed Services
 * UNSC Navy
 * Naval Command (NAVCOM)
 * Fleet Command (FLEETCOM)
 * Office of Naval Intelligence (ONI)
 * Beta-5 Division
 * Project SPARTAN-III
 * Prowler Corps
 * Signal Corps
 * Logistical Operations Command (NavLogCom)
 * Office of Investigations (OI)
 * Naval Special Warfare (NAVSPECWAR)
 * Project ORION
 * Project SPARTAN-I
 * Project SPARTAN-II
 * UNSC Marine Corps
 * UNSC Marine Infantry
 * UNSC Marine Aviation
 * UNSC Marine Logistics
 * UNSC Marine Military Police
 * UNSC Marine Special Operations
 * Orbital Drop Shock Troopers
 * UNSC Army
 * UNSC Army Infantry
 * UNSC Air Force

Rank Structure
The rank structure of the UNSCDF is similar in many ways, though most enlisted ranks are highly differentiated.

Bases, Outposts, and Command Centers
Unlike the UNSC, the UNSCDF probably has a larger network of operations bases and command centers on Earth. Aside from ground centers, the UNSCDF also operates the Orbital Defense Platforms about Earth and possibly even the Solar System.

Ground Bases

 * Crow's Nest, Africa, Republic of Kenya
 * Outpost C9, Africa, Republic of Kenya
 * HIGHCOM Facility Bravo-6, Australia
 * Base Segundo Terra, North America, Mexico, Mexico City
 * Diego Garcia, Indian Ocean
 * Chawla Base, North America, United Republic of North America, Boston

Orbital Defense Platforms

 * Cairo Station
 * Malta Station
 * Athens Station
 * Nassau Station

UNSCDF Weaponry
The weapons used by the UNSCDF are manufactured to the highest standards in the UNSC. Despite this, they can rarely compete with Covenant weapons.

Major UNSCDF Events

 * Interplanetary War - 2160-2200
 * Jovian Moons Campaign
 * Rain Forest Wars
 * Martian Campaign
 * Inner Colony Wars - Unknown, probably 25th century
 * Human-Covenant War - 2525-2553
 * Fall of Reach
 * Battle of Earth
 * Battle of Mare Erythraeum