Level 1: Outside the Hangar. As you pan to the right just after killing the very first three guys in the game, there are 10 windows across the outside of the hangar. Two you must shoot as the screen moves over. Shoot the rest in the row between bad guys. If you missed the first two, you get one more chance. Just before you enter the hangar, you look up at a weird angle. In the top right corner, the two windows can be shot and "X Marks the Spot" can be entered.
Level 2: Shoot out all of the upper windows of the far back wall in the Hangar. Another can be found by shooting all the yellow barrels when you are the forklift.
When you enter the hangar and turn the corner there will be a blue emetgency light to the left of the screen. Shoot it!?As you start to move toward the trucks and you turn left to face the same area, there are two blue lights on the wall as you turn. If you shoot both of them quickly you will enter a secret room.
Level 4: Shoot every yellow box while you're riding on the STAAR jeep.
Level 5: Shoot the doorplate of the second door marked General Weatherby as the door is opening.
Level 6: Shoot all of the computer screens on the level to enter the secret "Egg-Cellent" level.
Level 7: Shoot all the yellow barrels at the first area where the four purple zombies are throwing barrels on the hill.
After the guys drop from the ceiling, you will come to a part where the floor raises up. There are many explosive boxes and barrels sitting around. Shoot all 24 and enter a secret room called "Get a Life." You get one free life and a chance to get your streak up to 100. Shoot at all times, even if the giant alien is not on the screen.