**READ**
here i am showing you an easter that you can use the Thunder gun in campaign, (Thunder gun is found in Zombies also)
Tuturial - 1) when you start out you throw a couple of grandes so you blow up the gas tanks
2) when you do that go where i go to the record mechine and hold X (or square for PS3)
3)when you do that the screen should shake (if not restart and do the steps again)
4) go throw the rest of the campaign and go until you get where you get in the room with a whole bunch of weapons
5)once there go the record mechine and hold X (or square) and you will see the screen shake.
6) once it shakes you will see the thunder gun appear on the wall
7) grab the thunder gun and have fun.