Actually, I think it's more like a mumomumumumumomumomumumumomum

No. That is a space marine reclaiming the heritage of a super-soldier, to make certain that his genetic awesomeness can be passed down to the next generation of super-soldiers.

Given that the Adeptus Astartes are hypermasculine supersoldiers and the only women around are virginal warrior nuns, it's a safe bet that Space Marines totally bum each other off constantly.

Around this time this game was made there was a Warhammer 40,000 out called "Space Marine" (because this is before the Black Library published millions of books about Space Marines).

In it, there's a scene where three recruits have the symbol of the Imperial Fists (which is, as you might guess, a fist) branded on their buttocks by their sergeant, after a naked hazing exercise.

Space Marines have always been very very gay.

It was. Every other missions has unlimited alien spawn points you have to constantly keep an eye out for. Eventually you would have to make a break for it past them and that's when shit hit the fan. The last mission had a set number of aliens and if you sat around eventually they'd come to you.