Try to get the bazooka & flamethrower's power to maximum. Use the bazooka as your main weapon. It can blow up obstacles & cause some heavy damage. If you find yourself unable to kill an enemy near you, quickly change to the flamethrower and melt them, then change back to the bazooka.
Never stay still, even if you are trying to shoot
someone or something. If you move around, it will
be harder for the Tan army to hit you; same with
the Bosses. If you miss an enemy, turn around and
come back for another pass, but do not stay
still. For heavy populated areas, go forward but
weave left and right as you do so. This will help
keep you alive until the next health bag.
The Shark Sub
To beat the shark sub, you must beat all the tan men that come out. Then hold L1 to aim high, and aim with 2nd analog control stick moving it left and right. Now just shoot the turrets on top of the shark sub to sink it. The shark sub is found at the end of level 2.