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