UNSC Navy

The Navy is the space combat element of the United Nations Space Command Defense Force. Its roles include ship-to-ship combat, orbital bombardment, the deployment of Longsword atmospheric and space fighters, and the method of delivery for Marine and Special Operations (ODST) forces through use of Human Entry Vehicles (HEVs). The UNSC currently has a significant fleet force, along with Longsword fighters, though much of the UNSC Navy was destroyed during the Fall of Reach. Currently, UNSC ship production is handled by the Reyes-McLees Martian Shipyards.

The primary offensive armament of UNSC spacecraft are Magnetic Accelerator Cannons (MACs). These are high velocity coilguns that are used to accelerate projectiles ranging in mass from 600 metric tons in the case of smaller warships, and 3,000 tons in the case of Super MAC platforms. These projectiles are composed of Titanium-A, depleted Uranium, and/or Tungsten with a ferrous (iron) core. In Super MAC platforms, they are accelerated to over 40% of the speed of light by twenty-three linear accelerator coils. Ship-based MACs have a lower velocity. The UNSC Frigate Gettysburg is quoted as firing a 600 ton shell at 30 kilometers per second. Before Reach fell, the Pillar of Autumn was equipped with a modified MAC that could fire three lighter projectiles instead of just one heavier projectile. It was originally intended to allow the Pillar of Autumn a better chance of disabling a Covenant ship, which was a feature required for a mission that was later scrubbed in Halo: The Fall of Reach.

UNSC warships also carry Archer missile pods for ship-to-ship engagements, which prove themselves most effective against unshielded targets. A common tactic among groups of UNSC ships is to hammer the target's shields with MAC weapons and then pummel it with Archer missiles.

UNSC ships also carry "Shiva" nuclear warheads, an advanced form of nuclear missile that is able to overcome the limitations of nuclear missiles in space, capable of generating EMP bursts even in vacuum.

As well as these, the UNSC mounts 50mm MLA CIWS for defense against enemy fighters and boarding craft, controlled by shipboard AIs.

UNSC warships are also equipped with significant Marine detachments for security, boarding actions, and planetary assault, and carry all the armor and firearms that could be needed by ground forces. It is implied that a significant portion of the interior of UNSC warships is devoted to this purpose.

UNSC ships also carry a number of C-709 Longsword Interceptors. These are armed with 110mm gatling Cannons and Anvil-10 ASMs. Alternatively they can be radio controlled and used to carry a Shiva that will detonate on impact, effectively destroying both the Longsword and its target.

Despite all of this firepower, however, UNSC warships can seldom defeat Covenant ships in an even engagement. It typically takes multiple hits from a ship-based MAC weapon to disable a Covenant ship's shields, although it was quoted in the game that an orbital MAC weapon can "put a round clean through a Covenant capital ship", and Archer missiles must be used in tremendous amounts to breach Covenant shield systems. Even with their shields down, Covenant ships have been noted to withstand direct hits from normal MAC rounds, and even their light ships can survive direct hits from Shiva nuclear missiles. This advantage in firepower and shielding gives the Covenant an effective 1:3 ratio or better against UNSC ships.