Twin boom

The P-38 Lightning, a successful twin boom aircraft

de Havilland Sea Vixen at an airshow in 2005

Twin-boom aircraft have their tailplanes and vertical stabilizers mounted on the tail of either two fuselages or on two booms fixed to either both sides of the single fuselage, the wings or the engine nacelles.

The reason for this design choice may be:

To be able to place a cargo door in the back of the aircraft (examples include the C-82 Packet and C-119 Flying Boxcar)
To construct propeller aircraft in pusher configuration or jet aircraft with the engine mounted directly to the aft of the fuselage (Bell XP-52, De Havilland Vampire)
For unobstructed field of view or field of fire to the rear (Focke-Wulf Fw 189)
Twin aircraft, constructed by putting two copies of an existing traditional aircraft side-by-side, (P-82 Twin Mustang, Heinkel He 111Z Zwilling, Messerschmitt Me 609)
To accommodate early inline engines and their lengthy turbochargers in the most aerodynamically efficient/practical planform (P-38 Lightning)
To increase an aircraft structure's rigidity, strength, and internal volume (Rutan Voyager, Scaled Composites Grizzly, Virgin Atlantic GlobalFlyer)