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B28 / Mk.28 / W28

The Mk-28 hydrogen bomb, although first produced in 1958, remained an active item until 1991. It was designed to be carried by various fighter and bomber aircraft (F-100, F-104, F-105, B-47, B-52, and B-66); the "28" warhead was also used in Hound dog and Mace missiles which have now been retired from service. This weapon is capable of a ground or air burst and may be carried internally or externally, with a free-fall or parachute retarded drop, depending upon its configuration.

The W-28 small diameter, light weight ("Class-D") thermonuclear warhead in this bomb became the most versatile and widely used design ever adopted by the United States. This tactical and strategic thermonuclear bomb had the longest US service duration (33 years) and 2nd largest production run of any U.S. weapon design (4500 produced -- all models); 20 models and variants; Mod 4 fission only; Cat A PAL3 (Mod 1), B (Mod 2), D (Mod 3, Mod 5); Single point safety problems with the primary were discovered after start of initial manufacture, production halted for 5 months.

The Mk-28 employed the "Building Block" principle, permitting various combinations of components:
B28EX--Carried externally by F-100, F-105, and F-4; no parachute.
B28RE--Carried externally; equipped with one 4-ft. pilot chute and one 28 ft. ribbon chute.
B28IN--Carried internally by B-52 and F-105; no parachute.
B28RI--Carried internally; equipped with one 4-ft. pilot parachute, one 16.5-ft. ribbon extraction chute, one 64-ft. solid chute, and one 30-in. stabilization chute.
B28FI--Carried internally; equipped with one 4-ft. pilot chute, one 16-ft. and one 24-ft. chute.

On 17 January 1966, during a mid-air refueling operation, a U.S. Air Force (USAF) B-52 bomber collided with a USAF KC-135 tanker over the coast of southern Spain near the village of Palomares. Palomares is in the province of Almer�a, which is a one and one-half hour flight from Madrid. Both aircraft were destroyed; 7 of 11 crew members perished. The B-52 carried four B28 nuclear weapons. Parachutes deployed for two weapons. One bomb was recovered intact from the dry Almanzora river bed east of Palomares and the other was recovered intact from the Mediterranean seabed 8 km offshore 80 days post-accident. Parachutes failed to deploy for two weapons which underwent high explosive detonation. One landed 1.7 km west of the village (Impact Zone #2) and the other landed at the eastern edge of the village (Impact Zone #3). This resulted in various amounts of radioactive contamination over 226 hectares (558 acres).

On 21 January 1968, a SAC B-52G crippled by fire and carrying four B28 thermonuclear weapons flew over Thule Air Base at low altitude, permitting six occupants to bail out. The stricken plane -- with one crewmember -- crashed onto the sea ice of North Star Bay seven miles to the west of the base. The bombs did not detonate. But despite safeguards against this, the conventional triggers detonated in the fire.