Silkworm

Hint: Temporary invincibility and clear enemies:
This trick can be done with either the helicopter or jeep.
Fire on the mines that you locate.
When one explodes, a ball of smoke will rise.
Jump into the smoke.
It will surround you and make you invincible for a short period of time.
Also, fire on the ball of smoke.
Keep firing until the smoke explodes.
This will clear the enemies on the screen.