The B57 nuclear bomb was a low-yield tactical nuclear weapon used by the United States during the Cold War.

Entering production in 1963 as the Mk 57, the bomb was designed for carriage by high-speed tactical aircraft. It had a streamlined casing capable of withstanding supersonic flight speeds. It was 3 m (9 ft 10 in) long, with a diameter of about 37.5 cm (14.75 in). Basic weight was about 227 kg (500 lb).

Some versions of the B57 were equipped with a parachute retarder (a 3.8 m/12.5 ft diameter nylon/Kevlar chute) to slow the weapon in its descent, giving the aircraft a chance to escape the blast (or to allow the weapon to survive impact with the ground in laydown mode) at altitudes as low as 15 m (50 ft). Various fusing modes were available, including a hydrostatic fuse for use as a depth charge for anti-submarine use.

The B57 was produced in six versions (mods) with explosive yields ranging from 5 to 20 kilotons. Mod 0 was 5 kT, Mod 1 and Mod 2 were 10 kT, Mod 3 and Mod 4 were 15 KT, and Mod 5 was 20 kT. The depth bomb version for the US Navy was 10 kT.

The B57 was produced from 1963 to 1967. After 1968 the weapon became known as B57 rather than Mk 57. 3,100 weapons were built, the last of which was retired in June 1993.

The B57 could be deployed by most U.S. fighter and bomber aircraft, or by some US Navy helicopters.