Added extra level "Ground attack", you get on the fighter like A-10.
"STEAM Achievement" of "Ground attack" was added.
The extra levels have been combined into one "Side Story".
I adjusted the game balance of level boarding a helicopter and added STEAM Achievement.
I modified the code to improve the game's operating speed.
If I add extra levels in the future, it will take the form of a free update, not a paid DLC.