Hold L Button + Up, then release
Hold R Button + C-Down, then release
Hold L Button + Left, then release
Hold R Button + Down, then release
Hold L Button + C-Left, then release
Hold L Button + R Button + C-Right, then release
Hold L Button + C-Up, then release
Hold R Button + Right, then release
Hold R Button + Right, then release
Hold R Button +C-Right, then release

You must have the Bunker level available already to use this code. This code must be entered on the mission selection screen.