On the level "Little Resistance" after you call in the airstrike go onto the beach and head towards the tank on the right.

Beside it will be a puddle, go into it. There will be a three more, go into all four of them and wait in the last one.

If you've done it right then the ground will start to shake and you will hear weird alien voices then four statues will come out of the ground all of them will be holding ray guns.

Grab them and have fun!