The UNSC Marine Corps, mostly referred to as the Marines, is a branch of the UNSCDF that is responsible for land-based military operations, as well as the protection of Naval vessels and installations from attack.
Battle of Installation 04
Main article: Battle of Installation 04
The surviving Marines from the Battle of Reach served an important role in the Battle of Installation 04, taking part in such engagements as securing the UNSC Pillar of Autumn crash site, launching multiple guerrilla assaults on Covenant convoys and base of operations and rescuing captured Pillar of Autumn's personnel from a Covenant Battlecruiser. Initially, the Marines were part of a special operation consisting of a sizable Orbital Drop Shock Trooper special forces detachment and a standard Marine detachment to infiltrate Covenant High Command and kidnap a Covenant Prophet.
- Marines now carry a myriad of weapons, far more than in Halo: CE, including Rocket Launchers. This allows them to be useful in more combat situations.
- Marines add extra firepower to any vehicle the player is driving. For vehicles like the Warthog, they are the only means by which it can drive and shoot simultaneously, as the player cannot drive and use their weapons alone.
- Marines can board Ghosts and assist the player in battles by driving them.
- Marines are not always careful when using their weapons, especially grenades and rockets. Thus, in some instances, they can accidentally injure or kill themselves, other marines, or even the player.
- Marines are not very durable and will easily go down in overwhelming gunfire. They struggle when fighting against tougher enemies, like Brutes, Elites, Hunters, and vehicles. Additionally, they are extremely susceptible to Flood Infection Forms.
- Living Marines no longer appear after 343 Guilty Spark (level) (and allies altogether disappear after the following level.) Thus, the player should try not to rely on Marines too much.
- When the Angry skull is turned on, Marines not only become hostile the player, but also friendly to the Covenant. As another consequence, every advantage listed above also becomes a disadvantage to the player with this skull enabled.
- In the Halo SPV3 level The Truth and Reconciliation, Captain Keyes tells a Marine to "Stow your bellyaching soldier -- remember, you're a leatherneck!" Leatherneck was a nickname earned by U.S. Marines in the era of the Continental Marines. The Marines would wear leather collars to provide protection from slashing attacks as they boarded enemy ships. Although an appropriate reference to Marines, the term "Leatherneck" and "Soldier" are viewed by their respective service members as being incompatible, and a means of differentiating between service in the Marine Corps or Army.
- Players have noted that the Marines tend to fight better against Master Chief than the Covenant, should the player betray his allies or have the Angry Skull activated. This is due to increased damage and accuracy values for the purpose of punishing the player.