For anyone who still cant find it because the youtube video is quite unclear here are instructions:
When the D-day crashes, call in the air strike (you dont have to do this, it just clears up the place) and go to the far right. You should find a puddle there, stay in it for 2-3 seconds.
Then, go to the left near the middle of the place, you should find another puddle although a little smaller. Stay in that one for a bit too, then go to the far left. You should find another puddle, stay in it for a few seconds while looking at everything ahead of you (the trees etc..NOT the sea.) A voice should start talking and 4 lions holding Ray Guns will appear.

Edit: I doubt thats the only place with the Ray Gun, there's probably one on all missions, but what I'm guessing is that the only one they found is the one on Little Resistance.