"Gunship 2000", as well as other simulators from MicroProse, needs the keymap to be US to work properly. Back in the days, you were supposed to enter "KEYB US" before playing.
This wasn't a problem before in DOSBox because it used Keyb US as default anyway, but since 0.73 (I think) it tries to automatically load the closest DOS keymap to your Windows settings.
So in short, either type KEYB US before the executable, or creat a TXT file containing these lines of text:
@ECHO OFF
KEYB US
GS2000.COM
KEYB [WHATEVER BELONGS HERE] […]
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@ECHO OFF
KEYB US
GS2000.COM
KEYB [WHATEVER BELONGS HERE]
Then save it to WHATEVER-YOU-WANT.BAT and place it in your GS2000 folder, and use this file to load the game from now on.