This demo shows how to get the Omega cannon on level 13. This is the first appearance of this powerful weapon.

There are three keys to getting the Omega:

1. The weapon is protected by two secret doors. The first one, inside the area containing the yellow key is initially locked. To unlock it, you must trip a switch in an inner room that is nearby.
2. Inside this secret door, you can see the cannon through a permanent grate. Eventually, you can open the second secret door from this vantage point, but you must first remove a temporary wall by tripping another switch. The tricky part is that this switch is behind the grate, around the tight corner. You cannot see it. :-( There is probably not enough maneuvering room to hit it with a guided missile (I'd really like to see some one prove me wrong! :-), but you can bounce a Phoenix cannon shot off the far wall into the switch. This exposes (barely) the second secret door. It's on the "floor" around the corner.
3. This second secret door can only be opened from the inside. (I hate those kind! :-) In addition, even using the afterburner, there is insufficient time to open this door "normally" (with lasers, flares, etc.) and get through it. So, the only alternative is a trusty guided missile. You must first use markers to prop open the first secret door and the standard door leading to the key area. Now, some recommend firing the guided missile from just under the second, open-only-from-the-inside door and guide it on a long circular path, through the grate, and into the door just above your head. I find it much easier to guide the missile from just outside the propped-open standard door, and there is ample time to get down the hallway and into the Omega chamber.

The demo clearly demonstrates the steps necessary to accomplish the task and obtain the weapon. Enjoy!