You'd think that with global terrorist threats and fighting two wars, the US Defense Department would have little time on its hands to start a circus troupe.

However, the Defense Advanced Research Projects Agency (DARPA) has filed a patent application for a contraption designed to hurl SWAT teams and other emergency workers onto the roofs of inaccessible tall buildings human cannonball style, New Scientist reports.

The lethal-looking device (pictured) consists of a forward-facing chair mounted on rails that point at an angle of up to 80°. Powered by compressed air, the foolhardy “payload” would shoot up until the saddle reaches the end of the rails, at which point he would flail free skyward.

The application is extremely detailed, with proposals for computer control, feedback mechanisms, and valve pneumatics. They don't seem to have considered in as much depth what happens once gravity takes over.

But no matter, the designers reckon a four metre high launcher could put a man on the top of a five storey building in less than two seconds.

Read the patent here. ®