Thundergun in Campaign

The Thundergun appears in the level "Numbers" as an easter egg, similar to the Ray Gun on "Little Resistance." The steps and video on how to do it are as follows:
1. After the interrogation scene ends there are six big white canisters to the front of the player. (Note they are not the small propane tanks on the ground; they are the big white ones)
2. Shoot all six canisters until smoke comes out. (Note you must shoot the canisters before your attackers do.)
3. Run past the ladder to a small room connected to where you first start the mission.
4. If done correctly the player will see a black tape sticking out of a cassette player next to the door way.
5. Hold down the action key and the tape will disappear from the cassette player, or the obvious shake in the screen as cue.
6. Continue on until you get to the first of Clarke's weapon caches, behind the fridge after the rooftop jump.
7. Look to the left and you should find a cassette player.
8. When at the cassette player, press the use button and notice the cassette go in.
9. If done correctly, notice the tape goes in and the player makes several tunes, and the screen shakes.
10. The Thundergun will appear on the wall above the cassette player.