Bruno Horgan was recruited by A.I.M. after he successfully created a device which cast beams capable of "melting" anything. He developed a giant proton cannon for them, as well as a force field with which to protect it.
Iron Man set out to put a stop to A.I.M. and located the cannon at one of their bases. Unable to damage it due to the force field, Stark attacked and destroyed three shield generators, which lowered the shield. He was then able to destroy the cannon.