Defense of Mars

The Battle of Mare Erythraeum was a battle where UNSC Forces led by Colonel James Ackerson that fought the Covenant Loyalist Forces on the surface of Mars. It was presumed that the UNSC forces were defeated, as Colonel Ackerson was taken prisoner after the engagement. It was possible that other Humans were taken as prisoners, but this is highly unlikely.

Military Forces
Considering that James Ackerson is an UNSC Army Colonel, the UNSC more than likely used Army infantry instead of Marines during this battle.