Press ~ during game play in single-player mode to display the console window, then activate the following cheats by entering the corresponding codes:

CHEAT FUNCTION - CHEAT CODE
Toggle God mode - tank.immortal <0 or 1>
Toggle unlimited ammunition - tank.ammo <0 or 1>
Set tank speed - tank.speed
Toggle easy driving - tank.easydriving <0 or 1>
Toggle car type steering - tank.carsteering <0 or 1>
Toggle tank debug interface - tank.activate <0 or 1>
List all console commands - help