Enter "2ndsquad" as a profile name in North American version of the game to unlock all levels and extras including "Infinite Ammunition", "Super Squad", and "Old Movie" modes. Alternately, enter "BAKERSDOZEN" as a profile name.
Successfully complete the game on the Easy difficulty setting to unlock Old Movie mode. This mode allows the game to be played in black and white.
Successfully complete the game on the Normal difficulty setting to unlock the "Infinite Ammunition" option.
Successfully complete the game on the Hard difficulty setting to unlock the Authentic difficulty setting. This mode has no checkpoints, saves, icons nor reticules.
Successfully complete the game in Authentic mode to unlock the "Super Squad" option.
Die four times after a save point and you will be asked if you want to heal your squad.
If you fire a Panzershrek and go to situational awareness before you throw away the gun, you will see that it still has the round blub that was supposed to be fired off.