Is it possible to go back in a level? I've just finished a part of a level/mission 14 where all my marines have been killed and it's impossible to finish the level without them. Additionally, i've exhausted all my sources of ammo.

Replay Mission button.
Replay the last mission. If you use the load menu chances are you'll get the no melee bug.

It's on PC, and i can't find the 'replay mission' option on the screen.

It's in the campaign menu.

Yeah, found it. Thanks. I was just wondering whether all the marines were meant to die? I've played the level again and all the marines died once again. Is it possible to get on god mode to test the theory out?

Also, will i be able to progress to other levels if i finish this one?