The B43 was developed from 1956 by Los Alamos National Laboratory, entering production in 1959. It entered service in April 1961. Total production was 2,000 weapons, ending in 1965. Some variants were parachute-retarded and featured a ribbon parachute.
The B43 was built in two variants, Mod 1 and Mod 2, each with five yield options. Depending on version, the B43 was 18 inches (45 cm) in diameter, and length was between 12 ft 6 in and 13 ft 8 in (3.81 m and 4.15 m). The various versions weighed between 2,060 lb and 2,125 lb (935 kg to 960 kg). It could be delivered at altitudes as low as 300 ft (90 m), with fusing options for airburst, ground burst, free fall, contact, or laydown delivery. Explosive yield varied from 70 kilotons of TNT to 1 megaton of TNT.
The B43 used the Tsetse primary design for its first fission stage, along with several mid and late 1950s designs.
Carrier aircraft included most USAF and USN fighters and bombers, including the A-4 Skyhawk, A-5 Vigilante, A-6 Intruder, A-7 Corsair II, B-47 Stratojet, B-52 Stratofortress, F-4 Phantom II, F-15 Eagle, F-16 Fighting Falcon, F-105 Thunderchief, F-111 Aardvark, F/A-18 Hornet, and FB-111A. The B-1B Lancer was also intended to carry the B43, though it remains unclear whether this particular aircraft was type-approved to carry the B43. It was also supplied for delivery by Royal Air Force Canberra and Valiant aircraft assigned to NATO under the command of SACEUR.
The B43 was never used in anger, but it was involved in a nuclear accident when an A-4 Skyhawk of the USS Ticonderoga (CV-14) (from attack squadron VA-56) was lost off the coast of Japan on 5 December 1965. The aircraft, the pilot, and the bomb were never found.