Here is the full list of all 15 Steam Marines achievements.
Lose the game on the Armory Deck.
Kill an enemy with a Lasershot.
Get a marine to Sergeant rank.
Knock an enemy out into space.
Beat the game on Easy difficulty.
Beat the game on Normal difficulty.
Beat the game on Hard difficulty.
Beat the game on Brutal difficulty.
Have a full squad with laser weapons.
Have a full squad of Sergeants.
Lose the game on the Command Deck.
Lose the game on the Engineering Deck.
Lose the game on the Medical Deck.
Lose the game on the Bridge Deck.
Lose the game on the Alien Deck.