Each submunition is contained within its own SAFU (safety and arming unit) and is telescoped shut. Upon release, the submunition is expanded by a spring. A focal distance stand off and detonating device deploys at the front and a fan of stabilising fins at the rear. Each has a shaped charge HEAT warhead for armour penetration, the casing of which is constructed from wound tessellated square wire, which produces around 1,400 anti-personnel fragments. A single cluster bomb produces a total of more than two hundred thousand fragments.

The weapon was developed in the early 1970s by Hunting Engineering, Ltd. of Ampthill, Bedfordshire but manufactured elsewhere at their production facility.

Each CBU-87 consists of an SUU-65B canister, a fuze with 12 time delay options and 202 submunitions (or bomblets) designated BLU-97/B Combined Effects Bomb. Each bomblet is a yellow cylinder with a length of 20 centimeters and a diameter of 6 centimeters. The BLU-97/B bomblets are designed to be used against armour, personnel and softskin targets and consist of a shaped charge, a scored steel fragmentation case and a zirconium ring for incendiaryeffects. The CBU-87 can also be equipped with an optional FZU-39/B proximity sensor with 10 altitude selections.

When dropped from an aircraft, the bomb starts spinning. There are 6 speeds that can adjust the bomb's rate of spin. After it drops to a certain altitude, the canister breaks open and the submunitions are released. Each bomblet has a ring of tabs at the tail end, these orient the bomblet and deploy an inflatable decelerator to decrease the falling speed of the bomblet. When the submunitions hit the ground, they will cover a large area and the CBU-87 can be adjusted so it can cover a smaller or wider area. Depending on the rate of spin and the altitude at which the canister opens, it can cover an area between 20x20 meters (low release altitude and a slow rate of spin) to 120x240 meters (high release altitude and a high rate of spin).

Manufacturers and the Department of Defense have claimed that the failure rate for each bomb is about 5%.^[2] This would mean that of the 202 bomblets dropped, about 10 will not explode on impact. Landmine Action has claimed the failure rate of the BLU-97/Bs used in the Kosovo campaign was higher, between 7 and 8 percent.^[3]

Overview[edit]

The CBU-97 consists of an SUU-66/B tactical munition dispenser that contains 10 BLU-108 submunitions. Each submunition contains four hockey-puck-shaped sensor-fused projectiles called Skeets. These detect target vehicles, such as tanks, armored personnel carriers, trucks and other support vehicles, and fire a kinetic energy penetrator downwards at them.

Operation[edit]

The 40 Skeets scan an area of 1,500 by 500 feet (460 m × 150 m) using infrared and laser sensors, seeking targets by pattern-matching. When a Skeet finds a target it fires an explosively-formed penetrator to destroy it. If a Skeet fails to find a target, it self-destructs 50 feet (15 m) above the ground; if this fails, a back-up timer disables the Skeet. These features are intended to avoid later civilian casualties from unexploded munitions, and result in an unexploded-ordnance rate of less than 1%.

As the CBU-97 approaches its designated aim-point, the dispenser skin is severed into three panels by an explosive cutting charge. The slipstream peels away these panels, exposing the 10 BLU-108 submunitions. An airbag ejects the forward five submunitions, then five in the aft bay. Following a preset timeline, the submunitions deploy parachutes so that they are spaced about 100 feet (30 m) apart. Then each submunition releases its chute, fires a rocket motor that stops its descent and spins it on its longitudinal axis, and releases Skeets 90 degrees apart, in pairs. Each spinning Skeet makes a coning motion that allows it to scan a circular area on the ground.

The laser sensor detects changes in apparent terrain height such as the contour of a vehicle. At the same time, infrared sensors detect heat signatures, such as those emitted by the engine of a vehicle. When the combination of height contours and heat signatures indicative of a target are detected, the Skeet detonates, firing an explosively-formed penetrator (EFP), a kinetic energy penetrator, down into the target at high speed, sufficient to penetrate armor plating and destroy what is protected by it. Even well-armored vehicles such as main battle tanks, while having massive armor protection on the front and sides, are only lightly armored above,^[2] and relatively easily penetrated. Each bomb can spread penetrators over an area of 15 acres (61,000 square metres) or more. According to an ABC News consultant, an attack by this bomb would basically stop an armored convoy moving down a road. While the bomb was designed during the Cold War for fighter-bombers flying at low altitude below radar cover to attack Soviet tanks, a single B-52 high altitude heavy bomber can destroy an entire armored division with these bombs, where in the past dozens of aircraft would have had to drop hundreds of bombs for the same effect.^[3]

The CBU-97, or CBU-105 version, is deployed by tactical aircraft from altitudes of 200 to 20,000 feet (60 to 6,100 m) Above Ground Level (AGL) at speeds of 250 to 650 knots (460 to 1,200 km/h).^[4]

The weapon was first deployed, but not used, during Operation Allied Force when NATO entered the Kosovo War. Sensor-fused weapons were first fired in combat during the 2003 invasion of Iraq.

In 2010 the US government announced the sale to India of 512 CBU-105 Sensor Fuzed Weapons.^[2] The expected platform is the SEPECAT Jaguar.^[5]

Saudi Arabia has also requested the CBU-105.^[6] In May 2015, Human Rights Watch reported on, and criticized, the Saudi use of the CBU-105 SFW during the Saudi Arabian-led intervention in Yemen.^[7][8]

History[edit]

In the 1950s through the early 1970s the M117 was a standard aircraft weapon, carried by the F-100 Super Sabre, F-104 Starfighter, F-105 Thunderchief, F-111, and F-4 Phantom.

The M117 series was used extensively during the Vietnam War, and B-52G Stratofortress aircraft dropped 44,600 M117 and M117R bombs during Operation Desert Storm.^[1][2]

At present it is used only by the B-52 Stratofortress; tactical aircraft now tend to use the Mark 80-series bombs, particularly the Mark 82 (500 pounds (227 kg)) or Mark 84 (2,000 pounds (907 kg)) bombs and their guided equivalents.

On 26 June 2015, the last Mk 117 in PACAF inventory was dropped by a B-52H crew on an island near Andersen AFB, Guam.^[3]

Design[edit]

When the Mk 20 bomb cluster is released from the aircraft, the arming wires (primary and/or optional arming) are pulled sufficiently to arm the Mk 339 fuze (and recently the FMU-140 fuze) and release the fins. The positive armed fin release arming wire frees the fin release band, and the movable fins snap open by spring-force. Functioning of the fuze initiates the linear shaped charges in the dispenser which cut the dispenser case in half and disperse the bombs/bomblets. When the Mk 339 Mod 1 primary fuse arming wire is pulled, the fuze will function 1.2 seconds after the arming wire has been extracted. If the pilot selects the option time (4.0 seconds), both the primary and option arming wires must be pulled. If the pilot selects the option time and the primary arming wire is not pulled, the fuze will fail to function and be a dud.

Development & deployment[edit]

Developed for United States military forces in the 1950s, it was first used during the Vietnam War. The bomb consists of a cast steel case with 96 lb (44 kg) of Composition H6, Minol or Tritonal explosive. The power of the Mk 81 was found to be inadequate for U.S. military tactical use, and it was quickly discontinued, although license-built copies or duplicates of this weapon remain in service with various other nations.

Development of a precision guided variant of the Mk 81 bomb (GBU-29) was started due to its potential to reduce collateral damage compared to larger bombs, but this program has now been cancelled^[1] in favor of the Small Diameter Bomb.

Variants[edit]

• Mark 81 Snakeye fitted with a Mark 14 TRD (Tail Retarding Device) to increase the bomb's drag after release. The bomb's increased air-time, coupled with its (relatively) forgiving safe drop envelope, allowed for very low-level bombing runs at slower speed. Used commonly in the close air support role in Vietnam (prior to wider availability of GBU-series precision ordnance). Nicknamed "snake", as in the typical Vietnam support loadout of "snake and nape" (250-lb. Mk-81 Snakeye bombs and 500-lb. M-47 napalmcanisters).
• GBU-29 Joint Direct Attack Munition, a precision guided version of the Mark 81 (cancelled).^[1]

The Mk 82 is the warhead for the GBU-12 laser-guided bombs and for the GBU-38 JDAM.

Currently only the General Dynamics plant in Garland, Texas is Department Of Defense-certified to manufacture bombs for the US Armed Forces.

The Mk 82 is currently undergoing a minor redesign to allow it to meet the insensitive munitions requirements set by Congress.

Mk. 82 bomb with Tail Retarding Device – this photograph shows an unfuzed, museum display Mk 82 with its usual combat paint scheme. For display purposes, the optional high-drag "Snakeye" tailfins used for low-altitude release are shown.

According to a test report conducted by the United States Navy's Weapon System Explosives Safety Review Board (WSESRB) established in the wake of the 1967 USS Forrestal fire, the cooking off time for a Mk 82 is approximately 2 minutes 30 seconds.

More than 4,500 GBU-12/Mk 82 laser-guided bombs were dropped on Iraq during the Persian Gulf War.^[2] France requested 1,200 MK82s in 2010 to Société des Ateliers Mécaniques de Pont-sur-Sambre (SAMP) which builds MK82s under licence.^[3] Saudi Arabia requested 8,000 Mk82s in 2015, along with guidance kits and other weapons.^[4]

• Mark 81 Snakeye fitted with a Mark 14 TRD (Tail Retarding Device) to increase the bomb's drag after release. The bomb's increased air-time, coupled with its (relatively) forgiving safe drop envelope, allowed for very low-level bombing runs at slower speed. Used commonly in the close air support role in Vietnam (prior to wider availability of GBU-series precision ordnance). Nicknamed "snake", as in the typical Vietnam support loadout of "snake and nape" (250-lb. Mk-81 Snakeye bombs and 500-lb. M-47 napalmcanisters).

Low-level delivery[edit]

In low-level bombing, it is possible for the delivering aircraft to sustain damage from the blast and fragmentation effects of its own munitions since the aircraft and ordnance arrive at the target very close to the same time. To address this issue, the standard Mk-82 General Purpose bomb can be fitted with a special high-drag tail fin unit. In this configuration, it is referred to as the Mk-82 Snake Eye.^[5]

The tail unit has four folded fins which spring open into a cruciform shape when the bomb is released. The fins increase the drag of the bomb, slowing its forward progress and allowing the delivery aircraft to safely pass over the target before the bomb explodes.

Low-level delivery[edit]

In low-level bombing, it is possible for the delivering aircraft to sustain damage from the blast and fragmentation effects of its own munitions since the aircraft and ordnance arrive at the target very close to the same time. To address this issue, the standard Mk-82 General Purpose bomb can be fitted with a special high-drag tail fin unit. In this configuration, it is referred to as the Mk-82 Snake Eye.^[5]

The tail unit has four folded fins which spring open into a cruciform shape when the bomb is released. The fins increase the drag of the bomb, slowing its forward progress and allowing the delivery aircraft to safely pass over the target before the bomb explodes.

The Mk 83/BLU-110 is used as the warhead for a variety of precision-guided weapons, including the GBU-16 Paveway laser-guided bombs, the GBU-32 JDAM and Quickstrike sea mines.

This bomb is most typically used by the United States Navy. According to a test report conducted by the United States Navy's Weapon System Explosives Safety Review Board (WSESRB) established in the wake of the 1967 USS Forrestal fire, the cooking off time for a Mk 83 is approximately 8 minutes 40 seconds.

The bomb has been controversially used during the Saudi Arabian-led intervention in Yemen.^[3]

The Mark 84 is capable of forming a crater 50 feet (15.2 m) wide and 36 ft (11.0 m) deep. It can penetrate up to 15 inches (381.0 mm) of metal or 11 ft (3.4 m) of concrete, depending on the height from which it is dropped, and causes lethal fragmentation to a radius of 400 yards (365.8 m).^[3]

Many Mark 84s have been retrofitted with stabilizing and retarding devices to provide precision guidance capabilities. They serve as the warhead of a variety of precision-guided munitions, including the GBU-10/GBU-24/GBU-27 Paveway laser-guided bombs, GBU-15 electro-optical bomb, GBU-31 JDAM and Quickstrike sea mines.^[4] The HGK is a Turkish guidance kit used to convert 2000-lb Mark 84 bombs into GPS/INS guided smart bombs.^[5]

According to a test report conducted by the United States Navy's Weapon System Explosives Safety Review Board (WSESRB) established in the wake of the 1967 USS Forrestal fire, the cooking off time for a Mk 84 is approximately 8 minutes 40 seconds.

The effects of MK-77 bombs are similar to those of napalm. The official designation of Vietnam War-era napalm bombs was the Mark 47.^[3]

Use of aerial incendiary bombs against civilian populations, including against military targets in civilian areas, was banned in the 1980 United Nations Convention on Certain Conventional Weapons Protocol III. However the United States reserved the right to use incendiary weapons against military objectives located in concentrations of civilians where it is judged that such use would cause fewer casualties and/or less collateral damage than alternative weapons.^[4]

The weapon can penetrate up to 40 centimetres (16 in) of concrete, and creates a crater 2 metres (6 ft 7 in) deep and approximately 5 metres (16 ft) in diameter. In addition, concrete slabs around the crater are disturbed in an area approximately 15 metres (49 ft) in diameter. The disturbed slabs are displaced up to 50 centimetres (20 in) above the original surface, making repair more difficult than the simple crater from a conventional bomb.^[1]

The Durandal was adopted by the US in a slightly modified form (with a steeper impact angle and a higher 630 knot deployment speed) as the BLU-107/B in the 1980s, and carried by F-111 and F-15E strike aircraft.^[1]