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