Unlock entire game - enter the following sequence at the mission select 
screen: 
LTHUMBSTICK BUTTON, BLACK, RTRIGGER, RTHUMBSTICK BUTTON, WHITE, LTRIGGER 

Switch front-end music - enter the following sequence anywhere in the 
front-end: 
LTHUMBSTICK BUTTON, LTHUMBSTICK BUTTON, RTHUMBSTICK BUTTON, RTHUMBSTICK 
BUTTON, LTRIGGER, RTRIGGER 

Spoof Mission Briefing - enter the following at the armoury screen before 
launching missions 1, 3, 6, 8, 9 & 14 only). 
LTRIGGER, LTRIGGER, RTRIGGER, RTRIGGER, LTHUMBSTICK BUTTON, RTHUMBSTICK 
BUTTON 

Complete current mission - enter the following sequence at any time during 
gameplay (not in the pause menu): 
LTHUMBSTICK BUTTON, WHITE, WHITE, BACK, RTHUMBSTICK BUTTON, WHITE 
==================================================================
Cheat Mode 
Go to the mission select screen. Once there, click down the Left analog, then press BLACK, R, click the Right analog, then press WHITE, then L. This will unlock everything in the game. 

Flak Cannon
The Flak Cannon works well at close range. Fire it at the first group of landing craft then use your pistol for the tanks at long range. 

Custom Soundtrack
Go to the options menu at the main screen. If you have already created your own soundtrack on the hard drive, you can listen to it during the missions.

Win Mission 
To win the mission you're currently playing, click the Left analog, then press WHITE, WHITE, BACK, click the Right analog, WHITE. 

Fake Mission Briefing 
Before certain missions (1, 6, 8, 9, 14), press L, L, R, R, then click the Left Analog stick, then the Right Analog stick before launch. You'll hear some funny business as a result.