Did you know you might have been sitting next to a person with a gun on your last flight? What if I told you they had that gun on the flight legally. Air Marshals have been flying with us since 1963. On 9/11/2001 there were only 33 Federal Air Marshals active. Now, although the official number is classified, the number is believed to be in the thousands. The current budget for Air Marshals is 800 million annually. Federal air marshals rollup under the TSA.
How many terrorists did the FAMs stop with this $800 million? Zero, according to a CNN Special Investigation (though agents did make four arrests last year – which averages some $200 million per arrest). OC Register
Read more about the federal air marshal program at wikipedia.