Twin tail

A twin tail is a specific type of vertical stabilizer arrangement found on the empennage of some aircraft. Two vertical stabilizers—often smaller on their own than a single conventional tail would be—are mounted at the outside of the aircraft's horizontal stabilizer. This arrangement is also known as an H-tail, as it resembles a capital "H" when viewed from rear - these were used on a wide variety of World War II multi-engine designs that saw mass production, especially on the American B-24 Liberator and B-25 Mitchell bombers, the British Avro Lancaster and Handley-Page Halifax heavy bombers, and on the Soviet Union's Petlyakov Pe-2 attack bomber.

A special case of twin tail is twin boom tail or double tail where the aft airframe consists of two separate fuselages, "tail booms", which each have a rudder but are usually connected by a single horizontal stabilizer. Examples of this construction are the twin-engined Lockheed P-38 Lightning; Northrop P-61 Black Widow; Focke-Wulf Fw 189; the single jet-engined de Havilland Vampire; cargo-carrying Fairchild C-119 Flying Boxcar and the little known Transavia PL-12 Airtruk.

Separating the control surfaces allows for additional rudder area or vertical surface without requiring a massive single tail. On multi-engine propeller designs twin fin and rudders operating in the propeller slipstream give greater rudder authority and improved control at low airspeeds, and when taxiing. A twin tail can also simplify hangar requirements, give dorsal gunners enhanced firing area, and in some cases reduce the aircraft's weight. It also affords a degree of redundancy—if one tail is damaged, the other may remain functional.

...
Wikipedia