Boeing proposed a 747 adapted as an aerial refueling tanker during the 1970s Advanced Cargo Transport Aircraft (ACTA) program that produced the McDonnell Douglas KC-10A Extender for the USAF. This is a summary of the aircraft modifications and flight tests of the proposed KC-33.
This is a nice refueling scene from the classic movie “A Gathering of Eagles”. During the refueling a fuel manifold bursts open in the cockpit of the B-52 and an emergency breakaway is executed. All electrical equipment is shut off and the aircraft is forced to perform a high speed flaps up landing resulting in hot brakes.