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