At the beginning of the mission "Little Resistance" get off the boat, call in the airstrike and go all the way to the right side of the beach.

You should see a big puddle, walk through it and in front of that puddle you should she a smaller one, walk through that one also.

Then keep on going straight "all the way to the left side of the beach" and you should see an average puddle.

Go to it and stay there for about 10 seconds.

Then you should hear alien voices and f4 "lions" should come out with the gun!

Retrieve the ray gun and have fun!