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