While the Mars-Sec seem to share many duties with the Marines, it appears that the Mars-Sec serve as the day-to-day regular UAC Security Guard force. Marines, on the other hand, tend to have more specialized jobs, such as being tasked with guarding special areas around the base (Marine Command for instance), as well as accompanying science teams being sent through the Portal. The security teams for the Delta Labs (Marines and Mars-Sec alike) are specially selected, due to the unique nature of research conducted inside Delta Labs. Because the UAC provides major funds and weapon research for the military, the government established an active duty Marine base on Mars to assist the UAC with extra security while the UAC continues to conduct research for new military weapons.