Here is the full list of all 28 Steam and Metal achievements.
Beat level 1.
1337 aircraft shotten.
666 aircraft shotten.
Accomplish level with rank F.
Level beaten without air-torpedos.
Destroy 24 aircraft continuously
Achieve accuracy 25%
Destroy 100 aircraft in one level.
Beat level 2.
Beat level 3.
Beat level 4.
Beat level 5.
Complete the game.
Destroy 69 aircraft continuously
Destroy 111 aircraft continuously
10000 aircraft shotten.
Achieve shooting accuracy 50%
Achieve shooting accuracy 77%
Level is beaten without a single scratch.
Kill 30+ enemies with a single(!) air-torpedo.
Beat the game on hard.
Pass through level without kill anybody but boss.
Take 1000+ bonuses on level.
Accomplish level without lossing a single life.
Accomplish level with rank A.
Destroy 200 aircraft in one level.
Destroy 300 aircraft in one level.
Beat game with score one million or more!