At the Main Menu hold the L button, then press left C, right C, top C, bottom C, A, top C, bottom C, left C, right C, start.
Classic Mode, Relentless Mode, and Credit Option
From main menu hold down right shoulder button then press left-c, up-c, right-c, down-c, B, left-c, down-c, right-c, up-c, start
Unlock Hidden Ships
Pause the game and hold the L Trigger then press Left C, Left C, Right C, Right C, B, A, Up C, Up C, Down C, Down C, Start
Unlock the Cheat Menu