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