Here is the full list of all 28 Steam and Metal achievements.
Beat level 3.
Destroy 200 aircraft in one level.
Level beaten without air-torpedos.
666 aircraft shotten.
Achieve accuracy 25%
Accomplish level with rank F.
Beat level 2.
Beat level 1.
Level is beaten without a single scratch.
Accomplish level without lossing a single life.
Destroy 100 aircraft in one level.
Destroy 24 aircraft continuously
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 50%
Achieve shooting accuracy 77%
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 with rank A.
Destroy 300 aircraft in one level.
Beat game with score one million or more!