B28 (nuclear weapon)

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A B28FI bomb is unloaded from a B-52H (1984)

The B28 (originally Mk 28 ) was a hydrogen bomb that was constructed as a free-falling aerial bomb with a variably selectable explosive force . It was developed for both the tactical and the strategic operational concept and entered service in 1962.

development

The B28 was created in response to a request from the United States Armed Forces in 1955. They needed a nuclear free-fall bomb that could be used by both bombers and high-speed tactical fighter aircraft . Development under the designation TX-43 (later TX-28) began in 1955 at Los Alamos National Laboratory in New Mexico . The TX-28 was u. A. Tested several times in 1956 as part of Operation Redwing . The first models were delivered to the United States Armed Forces in 1961 under the designation Mk 28 . After problems with the safety mechanism had to be fixed in the first models, the first weapons were ready for use in 1962.

construction

bomb

Five different types of bombs were made of the B28, all using the same W28 nuclear warhead. The bombs differed in the shape of the bomb shell, their safety devices and their ignition systems . Depending on the model type, the bomb could be dropped from a great height or from low altitude . The W28 nuclear warhead could be ignited in the air, close to the ground or on the ground, depending on the design and intended use. Depending on the model type, there was a parachute / braking parachute that reduced the speed of fall of the bomb. The B28 was designed to be dropped from bombers and supersonic fighter planes. There were variants that could be carried in the weapon bay or at external load stations . For this, the B28 is equipped with the standard bomb locks with 762 mm. The B28 bombs can be roughly divided into three sections. The ignition system is housed in the top of the bomb. Depending on the version, this included a time fuse , an impact fuse or a proximity fuse . The W28 nuclear warhead and its operating elements were housed in the middle section. Three or four stabilizing wings were mounted on the rear of the bomb. A parachute / braking parachute was also housed in the rear of the bomb, depending on the model type.

Nuclear warhead

The B28 was equipped with the W28 nuclear warhead, which was also used in the TM-76 Mace , the GAM-77 Hound Dog cruise missile and the British Red Snow bomb. The W28 nuclear warhead was a hydrogen bomb based on the Teller-Ulam design . In the W28, a boosted fission bomb with a floating core was used in the primary nuclear fission explosive device (fission fuse ) . This consisted of a hollow sphere of 239 plutonium filled with lithium deuteride ( 6 Li) and tritium gas . This sphere was coated with a layer of 235 uranium . An outer shell made of 238 uranium was attached to the hollow sphere . Above that was a neutron reflector made of a layer of beryllium . A cavity with a vacuum was located between the inner hollow sphere and the outer shell . The outer shell was fixed to the inner hollow sphere with aluminum cones. A neutron source, which presumably used 241 americium , was mounted on the outside of the spherical structure . For the ignition of this primary nuclear fission explosive device, explosive lenses made of Octol and later made of polymer-bound explosives of the type PBX-9508 were used. Next to the spherical nuclear fission explosive device was the cylindrical fusion stage. A core made of 239 plutonium, which was surrounded by lithium deuteride, was used as a so-called spark plug . This was in a coat made of 238 uranium. The cylindrical fusion stage was embedded in polystyrene , which was coated with beryllium. The entire W28 nuclear warhead was around 0.9 m long and had a diameter of less than 500 mm.

The W28 nuclear warhead was designed so that the explosive force could be selected in five stages. Of these five levels, four are known: 70  kT , 350 kT, 1.1 MT or 1.45 MT. The selection of the explosive force had to be made on the ground before the aircraft took off. To prevent accidental detonation in case of accidents or improper ignition of the nuclear warhead of B28 is the permissive action link (PAL) Type B equipped.

variants

B28EX

The model B28EX (EX stands for External) was designed for use from external load stations of supersonic fighter aircraft. For this purpose, the bomb cover was designed in a streamlined manner. A radar proximity fuse was housed in the top of the bomb . The bomb should be dropped from a great height. The ignition could take place both in the air and on the ground.

bomb length diameter span Weight
B28EX 4.32 m 500 mm 800 mm 925 kg

B28IN

The B28IN (IN stands for Internal) was designed for transport and dropping from the weapon bay of bombers. The B28IN had a streamlined bomb hull and was intended to be dropped from high altitudes. The ignition could take place with a time fuse both in the air and on the ground. The B28IN was the smallest model in the B28 family.

bomb length diameter span Weight
B28IN 2.40 m 500 mm 710 mm 898 kg

B28RE

B28RE

The model B28RE (RE stands for Retarded External) was designed for use from external load stations on supersonic fighter planes. The bomb shell had a streamlined geometry. A parachute / braking parachute was housed in the rear of the bomb, which reduced the speed of the bomb. A radar proximity fuse was housed in the top of the bomb. The bomb could be dropped from a great height with or without the parachute / braking parachute. The B28RE could also be dropped with the parachute / braking parachute from medium altitude. The ignition could take place both in the air and on the ground.

bomb length diameter span Weight
B28RE 4.20 m 500 mm 560 mm 984 kg

B28RI

The B28RI (RI stands for Retarded Internal) was designed to be transported and dropped from the weapon bay of bombers. The B28RI had a blunt tip. The front bomb body was filled with a honeycomb structure made of aluminum. After the parachute was dropped, this served as a deformation zone to absorb the impact energy when it hit the ground. The bomb could be dropped from a high altitude without the parachute / braking parachute or from low and medium altitude with the parachute / braking parachute. The ignition could take place both in the air and on the ground with a time fuse.

bomb length diameter span Weight
B28RI 3.38 m 560 mm unknown 1,061 kg

B28FI

B28FI for equipping a B-52 bomber

The model B28FI (FI stands for full fuzing internal) was designed for transport and dropping from the weapon bay of bombers. Like the B28RI, the B28FI had a blunt tip. The B28FI could u. A. be thrown from low altitude from a height of 90–180 m. The bomb was equipped with a parachute / brake chute, an impact fuse, proximity fuse and a time fuse. The B28FI could therefore be used in a wide range of applications:

  • free-falling height ignition (from a great height)
  • Altitude ignition after delay by parachute (from high and medium altitude)
  • free-falling impact ignition (from high and medium height)
  • Impact ignition after delay by parachute (from high and medium height)
  • delayed ignition after dropping from low flight ("laydown" drop)
  • delayed ignition after dropping from the climb (pulling up from the low flight - "toss" or "loft" drop)
bomb length diameter span Weight
B28FI 3.68 m 560 mm 800 mm 1,061 kg

status

The B28 was intended for use with the United States Air Force , Strategic Air Command , the United States Navy and NATO . From 1962 to 1972, six Canadair CF-104 squadrons of the Canadian Air Force stationed in Europe were equipped with American B28 bombs as part of the NATO weapons transfer . The squadrons were known as the RCAF Nuclear Strike Force . Further bombs were held for the Royal Air Force , which used them to equip Valiant and Canberra bombers , which were subordinate to NATO .

The number of B28 bombs produced is unclear and is between 1200 and 4500, depending on the source. From 1984 the B28 was eliminated and gradually replaced by the more modern B83 . The last B28 was removed from the United States' nuclear arsenal in 1995.

Accidents

2 damaged Palomares B28RI cases in the National Museum of Nuclear Science & History, Albuquerque

Several serious accidents occurred with B28 bombs:

Emergency aircraft

literature

  • Duncan Lennox: Jane's Strategic Weapon Systems . Edition 2001, 34th edition Edition, Jane's Information Group, 2001, ISBN 0-7106-0880-2 .

Web links

Commons : B28  - collection of pictures, videos and audio files

Individual evidence

  1. ↑ a b c d e f g h i j k l m Duncan Lenox: Jane's Strategic Weapon Systems, Edition 2001. 2001. p. 597.
  2. ^ A b c Richard K. Brown: Nuclear Weapon Diagrams. In: nuclearweaponarchive.org. The Nuclear Weapon Archive, May 1, 1995, accessed October 1, 2018 .
  3. ^ B28 Nuclear bomb ( Memento from June 4, 2009 in the Internet Archive )
  4. ↑ Complete List of All US Nuclear Weapons Complete List of All US Nuclear Weapons , The Nuclear Weapon Archive