Halo Alpha
Halo Alpha

That MAC gun can put a round clean through a Covenant Capital Ship.
— Avery Johnson[3]

An Orbital Defense Platform, also known as a MAC Platform,[4] was a type of large UNSC Space station, used to defend strategic locations of great importance, typically planets of high strategic value.

The stations were frequently placed in geosynchronous orbit and deployed in groups, or clusters, of two to five platforms. The well-equipped and large bridge of an ODP is suitable for directing large-scale engagements. Such was the case when Fleet Admiral Terrence Hood directed UNSC forces from an ODP during the Battle of Earth.[3]

Class History[]

They were originally proposed sometime before 2490 as Avery Johnson mentions that they were being proposed around the same time he shipped out for boot camp.[5]

At least one Moncton-class was operational above Reach in 2517.[6] More platforms were in place by 2527.[7]

Camber had at least two Moncton-class platforms in place by the 2530s. At least one of which was destroyed during the Battle of Camber.[8]

Fall of Reach[]

Main article: Fall of Reach
Magnetic Accelerator Cannon

Unknown class of ODP, about to fire during the Fall of Reach.

During the Fall of Reach, the planet was protected by 20 ODPs. Marines and the SPARTANs were deployed to protect the orbital platforms' planetside power generators but were ultimately unable to do so against determined enemy assaults. The disabling of the defense platforms was a major factor on the battle's outcome.[9]


The outbreak of the Human-Covenant war prompted a massive expansion of Earth's defenses. Even as late as the Battle of Reach preparations had not yet been completed; they were set to come online on September 14.[10] By October 2552, some 300 ODPs were operational.[5] Many of Earth's ODPs were named after points of interest that they roughly kept station over.

A portion and small section of the 300 platforms first saw action at the early stages of the Battle of Earth. Athens Station and Malta Station were each destroyed by conveniently placed Covenant Bombs installed by Covenant boarding parties, while Cairo Station only narrowly avoided the same fate as the other platforms thanks to John-117's removal of the Covenant bomb on board.[3]

The ODPs were also used later in the Battle of Earth after Truth's Fleet arrived, but the Covenant might have already destroyed numerous stations when Truth himself arrived at Earth on the Forerunner dreadnought in November.[11]


The ODP's of New Carthage were the testing grounds for the Mjolnir Powered Assault Armor/Infiltrator.[citation needed]

In 2557 several ODPs and the UNSC Fleet engaged the Mantle's Approach, hardly denting the ship until the UNSC Infinity took out the ship's shielding with the help of John-117.[12]

H5G Campaign-Guardian EMP

ODPs and UNSC ships about to be disabled by a Guardian.

By October 28, 2558, several Moncton-class ODPs were still in use over Earth. They were disabled when the Guardians were released by the Created during The Reclamation.[13]



Diagram of Cairo Station.


The Mk. V "Super" Magnetic Accelerator Cannon is the station's primary armament. By activating several sets of super conductive coils in a series which envelope the barrel, the Mk. V can launch a 3,000 ton tungsten/depleted uranium projectile at 11991698.32 meters per second. As noted by Sergeant Major Avery Johnson, the Mk. V can punch a hole clean through a shielded Covenant Capital Ship. Orbital Defense Platforms fire at around 12,000 kilometers per second, 4% of the speed of light.

The metals used on the Mantle's Approach were known to withstand blasts from ODPs.[12] Against Covenant shield technology, the rounds possess enough kinetic energy to punch through shields, cut through the ship, and, upon exit, still retain enough energy to destroy a second ship, and cripple a third ship.[citation needed]

It is theorized that if a ship's armor or shields were to absorb all the kinetic energy of a super MAC round, the release of thermal energy would still vaporize the ship. By receiving power from ground-based power plants, orbital platforms could achieve a recharge and reload rate as short as five seconds.

ODPs can also rotate to fire planetside.[14]


Orbital Defense Platforms do not posses their power supply on board-as such generators would consume far too much space and provide for quicker neutralization by hostile naval forces. Instead, ground-based generators transmit power to the stations. This allows for bigger, more efficient generators for the platforms. Each cluster is in geosynchronous orbit with its generator complex-contrary to the popular belief that the stations are in orbit with the cities or regions which they are named after.

However, the ground-based generators are also a great weakness, while the platforms are heavily armored and shielded, the generators can be easily overwhelmed and destroyed by Covenant ground forces. As such was the case in the Battle of Reach-a single Covenant cruiser was able to deploy sufficient ground forces to have overwhelmed the UNSC defense-had the Red Team SPARTAN-IIs not interfered.


Stations of the Line[]

Station Name Identity Code
Cairo Station UNSCDF-ODA142
Malta Station UNSCDF-ODA143
Athens Station UNSCDF-ODA144
Nassau Station N/A
Oaxaca Station N/A


  • All known Orbital Defense Platforms over Earth are named after cities on Earth, presumably the city each station is in geo-synchronous orbit above.
  • Two weeks after the Battle of Reach, when the UNSC Security Committee met at HIGHCOM in Sydney, it is mentioned by Colonel Ackerson that most of Earth's ODP'S would take ten days before being fully operational.[citation needed]
  • The kinetic energy of a single shell from an orbital defense platform would be equivalent to almost 1.3 gigatons of TNT, 1031.08 times the yield of the current world's largest nuclear weapon ever tested.