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