Knife Edge: Nose Gunner Codes -

Expert mode:
Hold L + R +C-Up, then press C-Right, C-Left, B at the Kemco logo. A "Super Hard" difficulty setting may now be selected.

Level select:
Select "Story" or "Team" mode, then hold C-Left + C-Right + C-Up + C-Down + R and press Right, Up, Left, Down when the level number is displayed.