My translate plugin for that page says:
In Switzerland the running time of the first national specialty course for the training of professional Sky Marshals. So far, the Canton Police Corps have developed their own flying policemen. The new training location by the federal government is secret - but not the order of Marshals: You should turn off terrorists on the plane - by all means.
air guns, obviously
Love your name relevant the question 
The most likely Bullet that would be used would by the Sky Marshal would be the Glaser Safety Slug http://en.wikipedia.org/wiki/Glaser_Safety_Slug
Bullet holes are virtually harmless to an aircraft hull. Aircraft are designed to be safe with holes or cracks up the size where they are easily seen by inspection. If it’s small enough so that you might night notice it, it’s not dangerous.
Are there media claims like that? I haven’t seen them.
That’s usually the case. The Glaser Safety Slug was designed for this very reason.
ETA: Aarrgh. Ninjaed by DaSilva.
You are completely right. I keep forgetting they were moved over there. The Coast Guard is arguably the most effective organization in the U.S. government and does not deserve to be so slighted. My sincerest apologies.
Which was a stupid change. An air marshal is a flag-rank officer in an air force. A sky marshal is a cop on a plane.
I had never heard the term until people starting asking questions about them post-9/11. Made me think of the blue guy from The Centurions for some reason.
Keep in mind the skin of an airliner is not armoured, it’s as thin as they can get away with.
As mentioned above, the ammunition would likely not be rhino-stopping massive ordinance Dirty harry uses. The point is not that a gun won’t go through the skin of the aircraft, although if it hits flesh first, likely it slows down enough that it won’t. The point is that a bullet will put a bullet-sized hole in the aluminum skin, and 10psi difference and a half-inch hole does not lead to massive fuselage skin failure, a decompression passenger-ejecting windstorm as first made popular in Goldfinger, etc. - it means the compressor works overtime, possibly can’t keep up and there’s slow loss of pressure and the oxygen masks pop down.
As mentioned up thread, a bullet hole wouldn’t even depressurize an airplane. Air is constantly being pumped into the fuselage, and there is an opening with an automatically actuated door called an outflow valve that lets enough air out to maintain the desired cabin pressure.
Here is a photo of the outflow valve on a Boeing 737: http://http://upload.wikimedia.org/wikipedia/commons/7/72/Outflow.jpg
For size reference, the aft cabin door sill can be seen at the top of the image. Obviously, a bullet hole somewhere in the pressure vessel could be easily compensated for by closing the outflow valve a smidge. Larger airplanes have more air coming in, larger outflow valves, and often more outflow valves. Any hole in the pressure vessel is smaller relative to the entire system. The outflow valves on a 747 are each about the size of a cabin window. Now I don’t know that pressurization could be completely maintained after the loss of a cabin window at altitude, but it wouldn’t be the end-of-the-world scenario that Hollywood might have you believe (assuming no other structural damage).
Glaser Safety Slugs - interesting.
Wikipedia:
Here’s a video showing tests fired on combinations of dry wall, water (in a 1-gal plastic milk jug), ballistics gel, and denim on a pork shoulder. What’s interesting is the visible spread pattern of the birdshot in the ballistics gel.
Glaser Safety Slug 9mm Gel Test; 5:24 video: https://m.youtube.com/watch?v=hFxG6Hpy3A4
