U.N. Squadron
Contributed by - Richard

Gamer skill level:
Highlight the "Game Level" selection under the options screen. Press
and hold A + X on controller two, and press the D-pad on controller
one to change difficulty levels until the Gamer level appears. 

Easy money:
Use a fully armed A-10 Thunderbolt for the green truck missions.
Constantly bomb the trucks while firing. You'll make tons of money!