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

For this cheat you must already have the Silo level available. This cheat must be entered on the mission selection screen.