The Northrop X-4 Bantam was a prototype small twin-jet aircraft manufactured by Northrop Corporation in 1948. It had no horizontal tail surfaces, depending instead on combined elevator and aileron control surfaces (called elevons) for control in pitch and roll attitudes, almost exactly in the manner of the similar-format, rocket-powered Messerschmitt Me 163 of Nazi Germany's Luftwaffe. Some aerodynamicists had proposed that eliminating the horizontal tail would also do away with stability problems at fast speeds (called shock stall) resulting from the interaction of supersonic shock waves from the wings and the horizontal stabilizers. The idea had merit, but the flight control systems of that time prevented the X-4 from any success.

Two X-4s were built by the Northrop Corporation, but the first was found to be mechanically unsound and after ten flights it was grounded and used to provide parts for the second. While being tested from 1950 to 1953 at the NACA High-Speed Flight Research Station (now Edwards Air Force Base), the X-4's semi-tailless configuration exhibited inherent longitudinal stability problems (porpoising) as it approached the speed of sound. It was concluded that (with the control technology available at the time) tailless craft were not suited for transonic flight.

It was believed in the 1940s that a design without horizontal stabilizers would avoid the interaction of shock waves between the wing and stabilizers. These were believed to be the source of the stability problems at transonic speeds up to Mach 0.9. Two aircraft had already been built using a semi-tailless design-the rocket-powered Me 163 Komet flown by Germany in World War II, and the British de Havilland DH.108 Swallow built after the war. The United States Army Air Forces signed a contract with the Northrop Aircraft Company on 11 June 1946, to build two X-4s. Northrop was selected because of its experience with flying wing designs, such as the N-9M, XB-35 and YB-49 aircraft.

The resulting aircraft was very compact, only large enough to hold two Westinghouse J30 jet engines, a pilot, instrumentation, and a 45-minute fuel supply. Nearly all maintenance work on the aircraft could be done without using a ladder or footstool. A person standing on the ground could easily look into the cockpit. The aircraft also had split flaps, which doubled as speed brakes.

Interesting Fact: It was barely large enough to hold a pair of J30 jet engines, a 45-minute fuel supply, a pilot, and instruments.
The first X-4 was sent to Muroc Air Force Base in late 1948, setting the way for a series of taxi tests leading up to its first flight on December 15th of that year. But the first X-4 would never fly again, as it was morphed into a second aircraft. Walt Williams, who headed the NACA Muroc Flight Test Unit, called the original aircraft a “lemon,” while the NACA instrumented version would include flights by legendary aviators like Chuck Yeager, Pete Everest, and Arthur Murray.