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