Defense of Mars

The Battle of Mare Erythraeum is a battle where UNSC Forces led by Colonel James Ackerson fought the Covenant Loyalist Army on the surface of Mars. It is presumed that the UNSC forces were defeated as Colonel Ackerson was taken prisoner after the engagement.

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