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[5.0] Modern Glide Munitions (1)

v3.0.1 / chapter 5 of 10 / not dated / greg goebel / public domain

* Although work on guided glide bombs went on the fade in the 1950s, technological advances and the US war in Vietnam resurrected them. Confronted with tough targets and strong air defenses in the bombing campaign against North Vietnam, the US Navy and Air Force developed glide bombs guided by television and laser beams, and such weapons have been refined ever since.

This chapter discusses the development and operational use of modern television-guided and laser-guided bombs. Such guidance systems are now being updated with precision navigation systems, based on the Global Positioning System (GPS) navigation satellite constellation, along with an inertial navigation system (INS) backup.

JDAM


[5.1] WALLEYE, HOBOS & THE EO GUIDED BOMBS
[5.2] THE PAVEWAY LASER GUIDED BOMBS
[5.4] GPS-GUIDED BOMBS: GAM / JDAM / AASM
[5.5] GPS-GUIDED BOMBS: WCMD / MOAB / SDB / MISCELLANEOUS

[5.1] WALLEYE, HOBOS & THE EO GUIDED BOMBS

* One of the problems with early glide weapons was the crudity of electronic technology available during World War II. TV and infrared sensors were still primitive, and suffered from poor performance and reliability. By the 1960s, TV was well established, and solid-state electronics were available to make electronics systems much more compact and reliable. The technology was finally ready for combat.

The start of the air war over Southeast Asia in 1964 gave the US military a strong motivation to come up with new and powerful guided weapons. Strike pilots reported that North Vietnamese bridges, important targets in the effort to constrict the flow of supplies to Communist insurgents in South Vietnam, were proving very difficult to destroy. The bridges were very hard to hit with unguided weapons, and though attempts were made to destroy them with Bullpup missiles, discussed in a later chapter, the Bullpup's warhead was too small, and the pilot had to give his attention to guiding the missile into the bridge using a hand controller, which left him unable to take evasive action against ground fire.

Both the US Navy and the US Air Force wanted better solutions. Research into new guided bombs in the 1960s followed two main paths: weapons guided by television or other imaging sensors, and weapons that locked onto laser light reflected by a target. This section discusses the TV-guided bombs, while the next discusses the laser-guided bombs.

* Both the Navy and Air Force developed their own bombs guided by television and other imaging sensors, or "electro-optic (EO)" sensors, as they are known in general.

The Navy effort to build an electro-optic guided bomb (EOGB) resulted in the "Walleye". This weapon was the product of Navy research begun in 1963, leading to the award of a production contract to Martin's Orlando Division in early 1966. The weapon was originally designated the "AGM-62", where "AGM" meant "Air to Ground Missile", but then the Navy decided that a glide bomb wasn't really a "missile" and dropped that designation.

The "Walleye I" was a purpose-built weapon, rather than simply a modified dumb bomb. It had four long-chord delta wings arranged in a cruciform pattern; a vidicon-tube TV camera in the nose; a spinner in the tail to drive an electrical generator and hydraulic pump; and a 375 kilogram (825 pound) warhead. The weapon was 3.44 meters (11 feet 4 inches) long, had a diameter of 32 centimeters (12.5 inches), a wingspan of 1.16 meters (3 feet 10 inches), and a weight of 500 kilograms (1,100 pounds). The wings were fixed but had control fins at the trailing edge.

The Walleye I went into operation with Navy Douglas A-4 Skyhawks in early 1967, with impressive results. In the first strike, a Skyhawk pilot put the bomb directly into a window of a barracks building. Of the 68 Walleyes expended over a period of seven months, 65 hit their targets accurately.

AGM-65 Walleye

In operation, the image provided by the Walleye's seeker was displayed on a TV screen in the controlling aircraft. The operator locked the crosshairs on the display onto a high-contrast scene element like a window or a door, set the fuzing option as needed, and then released the weapon. The weapon would then glide accurately into the target, guided by the target's contrast pattern.

Details of the seeker system's operation are unclear, but it seemed to use an analog pattern-matching scheme. One plausible scheme for seeker operation would be for it to convert the image into two analog electrical waveforms, one for the vertical axis of the image and one for the horizontal axis, with the amplitude of the waveforms reflecting scene brightness. The seeker control electronics would then detect the transitions in the waveforms corresponding to abrupt changes in scene brightness, and use them as "goalposts" to guide the missile to target.

What is clear is that the seeker needed to have a stable high-contrast pattern to work properly, and so it sometimes would break lock if the day were gray and hazy, or there were shifting clouds or sources of transient sun glare. In such cases, "fire and forget" actually turned out to mean that the weapon was fired and then forgot where it was going. However, when the weapon worked, it worked very well, with accuracies of a few meters.

The Navy was enthusiastic enough about the Walleye to configure A-6 Intruder and A-7 Corsair II strike aircraft to carry the weapon, and develop a 900 kilogram (2,000 pound) "Walleye II", known as a "Fat Albert". The Walleye II was built by Hughes under subcontract to Martin Marietta. It looked like a scaled-up Walleye I, 4.04 meters (13 feet 3 inches) long, with a diameter of 46 centimeters (18 inches), and a wingspan of 1.3 meters (4 feet 3 inches). The Walleye II went into service in 1974.

The Walleye II was followed in 1975 by the "Extended Range / Data Link (ERDL)" Walleye, which featured bigger wings for longer glide range and a more sophisticated guidance and control system. Most of the Walleye I and II weapons were upgraded to "Walleye I ERDL" and "Walleye II ERDL" configuration.

The ERDL system allowed an operator to monitor the Walleye's seeker over an "AN/AWW-9" (later "AN/AWW-13") datalink pod, and change the target lock after launch if necessary. The controlling aircraft wasn't necessarily the same as the launch aircraft. As AZON drops in Burma had shown over two decades before, it was better to have one aircraft stand off from the target and guide the bombs, while others released them and got out of the target area. That not only enhanced effectiveness and increased crew safety, but meant that not all the strike aircraft needed to be fitted with the datalink pod. An updated "digital phase-shift keying (DPSK)" guidance system with a more reliable communications channel was retrofitted in the 1980s, resulting in the "Walleye I ERDL DPSK" and "Walleye II ERDL DPSK".

The Walleye was also obtained in small quantities by the USAF, as well as the Israeli Air Force. The Israelis used Walleye IIs in the Yom Kippur War in 1973 with mixed results, and then came up with a modified version, the "Tadmit", with an improved seeker and a booster rocket, that was used successfully in the 1982 war in southern Lebanon. The US Navy used Walleyes to good effect in the Gulf War, dropping 124 of them on Iraqi targets. The weapon was finally withdrawn from service in 1995. Inert Walleye training rounds were built, and even a nuclear-tipped Walleye, though it is unclear if the nuclear variant ever reached operational status. About 5,000 Walleyes of all types were built.

* In 1967, the US Air Force, working with Rockwell International, began development of their own EOGB. The first weapon in this series materialized in combat over Southeast Asia in 1969 as the "GBU-8/B HOBOS (Glide Bomb Unit 8, Homing Bomb System)".

HOBOS consisted of a kit, designated "KMU-353/B", that could be fitted to a Mark 84 900 kilogram (2,000 pound) or Mark 118 1,350 kilogram (3,000 pound) bomb. The kit included a tailfin section that had four square fins and contained a battery and control and communication electronics, and a nose section that contained an EO seeker system. The two sections were linked by four long slender fins, or "strakes", and an umbilical conduit that ran along the length of the bomb from the tailfin section to the nose section. A HOBOS weapon based on the Mark 84 slick bomb was 3.78 meters (12 feet 5 inches) long, had a span of 1.12 meters (3 feet 8 inches), and weighed 1.016 tonnes (2,240 pounds).

The EO seeker head was based on either TV or imaging infrared technology, though it appears there were a number of experiments with other options. Like the Walleye, the seeker in principle had a "fire and forget" capability, in which the operator could lock it onto a target. After release, the bomb glided directly to the target on its own by maintaining focus on the target's contrast pattern. Also like the Walleye, occasionally "fire and forget" meant the weapon would forget where it was going -- but when it worked, it worked well.

* After the end of the war, the Air Force and Rockwell continued development of the weapon through the 1970s, eventually coming up with the improved "GBU-15/B EOGB", originally the "AGM-112", which had either a TV or infrared guidance system. The TV-guided "GBU-15(V)1/B" became operational in 1983, and the infrared-guided "GBU-15(V)2/B" became operational two years later. The weapon has been fielded with the USAF and the Israeli Air Force, with the Israelis using it effectively in Lebanon in 1982.

GBU-20/B Planar Wing Weapon

The GBU-15/B is actually a family of weapons based on a kit of standard components, and is known as the "modular guided glide bomb" system. The Air Force also worked with Hughes to build a glide bomb with a pair of "switchblade" pop-open wings for extended glide range, but this "GBU-20/B Planar Wing Weapon (PWW)" never reached production.

The GBU-15/B is conceptually similar to HOBOS, with tail and nose sections that can be strapped to a 900 kilogram (2,000 pound) Mark 84 GP bomb. The kit can be attached to some other munitions, and has also been evaluated with a cluster munition canister, though this option was never deployed.

The standard GBU-15/B with a Mark 84 has a length of 3.5 meters (12 feet 10 inches), a wingspan of 1.49 meters (4 feet 11 inches), and a weight of 1.125 tonnes (2,500 pounds). The EO seeker permits fire and forget operation, or command guidance through an "AN/AXQ-14" datalink, or the later "AN/ZSW-1" datalink. Datalink guidance allows the bomb to be released from above an overcast layer, with the bomb falling under command guidance until it penetrates the cloud layer, where it is then locked on to the target.

GBU-15 airdrop from F-4 Phantom

The GBU-15/B had a distinctively different appearance from HOBOS, however, with triangular nose fins on the seeker section and large truncated delta fins on the tail section, with both sets of fins arranged in a cruciform pattern. As a result, the GBU-15/B is sometimes referred to as the "cruciform wing weapon (CWW)". The larger fins give the GBU-15/B a longer glide distance than HOBOS.

The GBU-15/B is carried by the F-15E Strike Eagle, and was carried by the F-111 Aardvark, now retired from US service. The F-111 made very effective use of the GBU-15/B during the Gulf War, dropping 71 of the weapons to seal off oil manifolds wrecked by the Iraqis to spew out oil, and other targets.

GBU-15/B CWW EOGB

GBU-15/B kits have been developed that feature smaller "short chord" wing, and the kits can be used on the BLU-109/B 900 kilogram (2,000 pound) penetrator warhead. This gives a "Chinese menu" of possible weapon configurations:

   designation      warhead     wings  guidance
   ____________________________________________

   GBU-15(V)1/B     Mark 84      long     TV
   GBU-15(V)2/B     Mark 84      long     IR 
   GBU-15(V)21/B    Mark 84     short     TV
   GBU-15(V)22/B    Mark 84     short     IR 
   GBU-15(V)31/B    BLU-109/B   short     TV
   GBU-15(V)32/B    BLU-109/B   short     IR 
   ____________________________________________

BACK_TO_TOP

[5.2] THE PAVEWAY LASER GUIDED BOMBS

* The invention of the laser in the early 1960s led immediately to excited visions of "death rays" that could shoot down enemy missiles, but such "directed energy" weapons proved a major challenge, and are only now beginning to seem practical. The laser did, however, have significant short-term potential for use in combat.

Using a laser as a weapon itself places enormous demands on device physics and energy supply, but the fact that a laser beam can be precisely pointed and remains tightly organized ("coherent" in laser terminology) over long range meant that it could be used as a precise pointing device. A laser could be strapped to a telescope with crosshairs so that the beam could be focused to "illuminate" a particular target to "mark" or "designate" it. The fact that the laser also generates a narrow range of colors ("monochromatic") also meant that the light reflected off such a target could be easily detected by simple sensors through a filter lens. A guided weapon could be fitted with such a sensor, with the sensor linked to feedback-control mechanisms so that it would home in on an illuminated target.

The idea of using a laser to designate targets apparently was devised in 1960 by two civilian engineers, David J. Salonimer and Norman Bell, at the US Army Missile Command in Huntsville, Alabama. The two were interested in building laser-guided artillery shells, and conducted studies on laser designator and seeker systems. Salonimer managed to get a little funding, and worked with Weldon Word of Texas Instruments (TI) to modify a Shrike anti-radar missile, discussed in a later chapter, as a laser-guided surface-to-surface weapon. The experiment didn't work out, but the idea of laser-guided weapons didn't go away.

Inspired by the Shrike experiment, Martin Marietta performed experiments of their own with laser targeting systems, and in 1964 demonstrated such a device to the Air Force, leading to a modest contract to TI the next year for an experimental demonstration of a "laser-guided bomb (LGB)". TI engineers built a laser seeker, based on an airflow test probe fitted to the nose of a bomb on a universal joint. The unit looked like a badminton "birdie", and so was called a "birdie head". It controlled the movement of four fins, which were originally fitted to the tail of the guided bomb.

The seeker had an optical sensor, shielded by a filter lens that was transparent to laser light but blocked light of other wavelengths. The sensor was a simple array of photodiodes, arranged in quadrants. The quadrant that picked up the most light energy activated the fins, which were operated in a "bang-bang" control mode: they were either deflected completely to one or the other limit of their range of movement, or remained straight. The fins operated in pairs arranged symmetrically around the guided bomb to shift the weapon up and down, or left and right.

Early tests were conducted with M-117 bombs with moveable tailfins, resulting in the TI "BOLT-117", the first LGB, which was tested in April 1965. Results were poor, but much improved accuracy was obtained with the use of the more aerodynamic Mark 84 "slick" bomb, and control fins attached to the nose of the weapon, instead of the tail.

The TI group, working on a shoestring budget with the USAF Armament Development & Test Center at Eglin, conducted tests through the rest of 1965 and 1966. After some work, the bombs became very accurate, though due to the bang-bang control scheme the bombs did have a tendency to bob up and down along the laser beam until they locked on target. Despite the lack of gyrostabilization systems, the bombs generally locked on solid after a few seconds.

TI was finally awarded a contract for 50 "Paveway" guidance kits, where "Paveway" is sometimes said to be derived from the "Precision Avionics Vectoring Equipment (PAVE)", though it seems more likely that the name was arbitrary and the acronym was invented after the fact. Prototype LGBs were sent to Vietnam in 1968 for operational testing, with mixed results. F-4 Phantom fighter-bombers were used in the tests, with the "weapons system officer (WSO)" in the back seat marking a target with a hand-held laser system designated the "Airborne Laser Designator (ALD)". It proved very difficult to keep the laser aligned on the target, but half the LGBs hit the target anyway.

* The tests led to the "Paveway I" munitions. They consisted of a kit that was attached to ordinary Mark 82 225 kilogram (500 pound), Mark 83 450 kilogram (1,000 pound), and Mark 84 900 kilogram (2,000 pound) bombs. The kit included a laser seeker head attached to four control fins in a cruciform arrangement, which was attached to the front of the bomb, and a set of four larger fins, also in a cruciform arrangement, which was attached to the rear of the bomb to provide some limited glide capability. All the LGBs used the same seeker head, but had different fin assemblies to accommodate different types of bombs.

The LGBs had their own power supply, consisting of a thermal battery for the electronics, along with a hot gas-driven actuator to move the seeker head. They did not require any electrical connection to the aircraft. They could be launched by any aircraft that could carry ordinary bombs of the same size, and could be guided by a laser designator on the launch aircraft, on a spotter aircraft, or operated by ground forces. The Air Force developed a laser designator for the F-4 under the code name "Pave Knife". This consisted of a laser slaved to a TV camera and allowed the Phantom back-seater to hit a target while the pilot concerned himself with evasive action.

The Paveway I kits were designated as follows:

Kits were also developed for other unitary bombs and cluster munition canisters, but it is unclear if these other weapons were fielded. The LGB kits only cost a few thousand dollars US, and were produced in great quantity. Tens of thousands of them were used in Vietnam, proving themselves in the North Vietnamese ground offensive into South Vietnam in the spring of 1972, and the LINEBACKER bombing campaign late in that year. 225 kilogram (500 pound) Paveways scored direct hits on North Vietnamese tanks, and 900 kilogram Paveways destroyed bridges that had survived repeated conventional bombing raids.

laser-guided bomb in test

* The initial Paveway design gave way to an improved series, known as "Paveway II", in the early 1970s. These weapons featured a enhanced but simpler and cheaper seeker head, and pop-out fins for the rear assembly to improve the weapon's glide characteristics, and make it easier to fit to aircraft. The new LGBs based on the Paveway II were given the following designations:

The British RAF also adopted a 450 kilogram (1,000 pound) Paveway II variant known as the "Mark 13/18", which was used by Harrier strike aircraft during the Falklands War in 1983. GBU-10C/B bombs were used by F-111 strike aircraft in the 1986 EL DORADO CANYON punitive raid on Libya.

The US Navy wanted to increase the range of their Paveway II weapons, and so devised a variant fitted with the solid rocket motor from a Shrike missile. This weapon is based on the Mark 83 bomb and is known as the "AGM-123 Skipper II". A Skipper II was used in 1988 during the Persian Gulf convoy operations to sink an Iranian frigate.

* The Paveway II required the launch aircraft to operate from medium altitude so that the bomb would have direct path to the target. This left the aircraft vulnerable to ground defenses, and so in 1976 the USAF issued a requirement for yet another generation of Paveway weapons, the "Paveway III".

The Paveway III used larger rear fins and a "smart" seeker head that incorporated a microprocessor-based digital autopilot, coupled to a more sensitive seeker with a wider field of view. Unlike earlier Paveway seekers, the seeker head on the Paveway III did not pivot, and the weapon did not use "bang-bang" control, instead following as straight a path to the target as possible. Bang-bang control was simple, but wasted much of the bomb's kinetic energy and reduced its range. The bomb could be released at low altitude and then sail almost level into the target area, where it could then dive directly into a target. However, tests of the improved LGB kit with 225 kilogram (500 pound) bombs showed such weapons to be unstable, so the USAF only fielded the 900 kilogram (2,000 pound) version, with test and evaluation completed in 1986.

The 900 kilogram (2,000 pound) Paveway III was known as the "GBU-24/B". The kit could be fitted to the standard Mark 84 bomb or the hardened penetrator BLU-109/B bomb. An improved Paveway III kit was used with the F-117 Stealth fighter and was known as the "GBU-27/B". The USAF worked on an "Advanced Unitary Penetrator (AUP)" munition externally similar to the BLU-109, but achieved twice the depth of penetration by the interesting method of shedding its outer layers. It was not adopted for service, apparently because even better ideas were in the works.

Confronted with deeply-buried Iraqi command bunkers, the USAF found that even Paveway IIIs built around the hardened BLU-109 bomb weren't good enough, and a crash program was put in motion to build something better. The new "bunker-busting" bomb, the "GBU-28/B", was prototyped in 17 days, using scrapped 203 millimeter (8 inch) artillery barrels with Paveway III kits attached. A single test drop was performed at the Tonopah Test Range in Utah, with the bomb burying itself so deep that it could not be found. More GBU-28/Bs were quickly built, airlifted to the Gulf, and immediately used to attack hardened Iraqi installations. Each GBU-28/B weighed 2,250 kilograms (5,000 pounds). It consisted of a guidance kit attached to a BLU-113/B core munition, mentioned in an earlier chapter.

The GBU-28/B was also used in the American war in Afghanistan in the winter of 2001:2002, carried by B-52s and F-15Es, which are the only aircraft currently qualified to carry the weapon. Only a limited batch was built in the first place, and stocks ran low during the campaign. The Air Force has since obtained a batch of "GBU-28C/B" bombs based on the new BLU-122/B penetrating bomb.

US laser-guided bombs

Some 9,000 Paveway II and III munitions were dropped during the Gulf War. Video recordings taken by targeting systems showed Paveways and other smart munitions dropping into the front doors of aircraft shelters and falling into the ventilation shafts of buildings, blowing them apart with satisfying effect. These proved a striking and impressive propaganda tool for US forces. Videos that showed the gruesome effects of high explosive blasts on humans were, understandably but a little dishonestly, not released to the public. One Paveway was even used to blast an Iraqi helicopter out of the sky, an action-movie stunt that probably amused one side of the transaction immensely.

During the Anglo-American invasion of Iraq in the spring of 2003, US forces used 225 kilogram (500 pound) LGBs filled with concrete as "minimum collateral damage" munitions to perform precision attacks on targets in built-up urban areas. These weapons were designated "GBU-45/B". The British also used practice LGBs filled with concrete during the campaign. The idea of turning an LGB into a "smart rock" was dreamt up by the Israelis during their squabbles with the Palestinians. The Americans later fielded a "Low Collateral Damage Bomb", which was a core munition with a composite case and modified explosive filler to reduce damage outside the immediate impact area, allowing the weapon to be used in built-up areas.

Most Paveway IIs have been updated with Paveway III technology. Hundreds of thousands have been produced, and tens of thousands used in combat. New LGBs continue to be developed: in 2008, Lockheed Martin demonstrated a 45 kilogram (100 pound) LGB named "Scalpel" for the US Navy and Marines. As the name implied, Scalpel was intended as a low-collateral-damage precision strike weapon for close combat, and its light weight makes it ideal for small UAVs. It is unclear if there is any commitment to production, however.

* Although the Paveway munitions have been sold to many countries, as with simple dumb bombs LGBs are a relatively straightforward technology and indigenous designs have been built in other countries.

British Aerospace and Matra of France sell the "BGL (Bombe a Guidage Laser) 1000" munition, which despite its name is an 850 kilogram (1,870 pound) weapon. It features pop-out tailfins. They also offer a smaller "BGL-400", which as its name implies is a 400 kilogram (880 pound) weapon. As mentioned, the Aeronavale BANG-150 and BANG-250 bombs can be fitted with laser guidance as well.

The Israelis have developed seeker kits for the standard Mark 82, 83, and 84 bombs. Israel Aircraft Industries (IAI) developed a laser seeker kit known as "Guillotine", which has now been replaced by a next-generation laser seeker kit known as "Griffin". IAI has been working on a new laser seeker system named the "Advanced Laser Guided Bomb (ALGB)" with improved accuracy. Elbit of Israel has also introduced a seeker kit known as "Whizzard" that offers a menu of different seeker options: laser seeker ("Lizard"); laser seeker with GPS-INS ("GPS-Aided Lizard / GAL"); infrared seeker ("Opher"); and infrared seeker with GPS-INS. The Opher's seeker is said to be smart enough to ignore burning vehicles and concentrate on legitimate targets.

* The Soviets of course have developed LGBs, based on their FAB series bombs, such as the 1,500 kilogram (3,300 pound) "KAB-500L", which is available in both HE and penetrator versions, as well as EOGBs, such as the 500 kilogram (1,100 pound) "KAB-500KR".

Interestingly, the Iranians, who have demonstrated considerable ingenuity in maintaining their military forces despite Western arms embargoes, have developed their own LGB, known as the "Sattar-2". Few details of this weapon are known, but it appears to be a rocket-boosted weapon.

BACK_TO_TOP

[5.4] GPS-GUIDED BOMBS: GAM / JDAM / AASM

* Laser-guided bombs don't work very well in bad weather, or the dusty and smoky conditions that can often occur in combat. The US military has long wanted a true fire and forget guidance system, where the weapon could simply be given target coordinates and then destroy it.

In the early 1990s, the US military completed its GPS navigation satellite constellation. The satellites of the GPS network transmit signals that allow a device with a GPS receiver to determine its own location to within a few tens of meters or better. GPS allows a weapon to be given coordinates and find the target on its own. Since GPS signals are faint and in principle can be easily jammed, it is important for a GPS-guided munition to have a backup INS based on fiber-optic gyroscopes or solid-state accelerometer sensors, to keep the weapon on course if it can no longer acquire GPS signals.

GPS-INS guidance doesn't obsolete EO or laser guidance schemes, which have higher precision and are usually better suited for attacks on mobile targets whose coordinates can't be easily determined in advance. However, it has proven useful to equip both the older EO and laser-guided systems with a backup GPS-INS guidance systems to allow them to stay on course even if seeker lock is lost.

* After the Gulf War, the USAF decided to develop a GPS-guided bomb known as the "Joint Direct Attack Munition (JDAM)". In particular, the USAF wanted to have a precision weapon for their new B-2 stealth bomber to make use of the aircraft's impressive attack capabilities. The B-2 featured a precision, all-weather "GPS-Aided Targeting System (GATS)", and a GPS-guided bomb coupled to GATS was exactly what was needed. However, JDAM wasn't scheduled to become available until late in the decade, which left the B-2 without a precision attack capability for several years. As a result, Northrop Grumman proposed a fast-track program to provide a "GPS Aided Munition (GAM)" until JDAM came along.

The result was a kit for a Mark 84 900 kilogram (2,000 pound) bomb. The kit consisted of a tailpiece that contained control electronics, and a "jacket" that was wrapped around the nose of the bomb. The tailkit had moveable fins, along with a guidance system and thermal battery, and was linked to the launch aircraft over an umbilical connection that allows downloading GPS coordinates. The jacket had strakes mounted on it at an angle to keep the bomb properly oriented as it fell.

The resulting weapon was originally designated "GAM-84" but later redesignated "GBU-36/B". Initial drop tests were conducted in June 1995, leading up to a demonstration in October 1996. Three B-2s dropped 16 live GAMs on 16 targets, with the first bomber dropping eight GAMs and the following two bombers dropping four each. The last bomber performed damage assessment, and showed that all 16 targets had been hit and destroyed in a single pass of the three aircraft. GAM could hit a target up to 24 kilometers (15 miles) away, and its "circular error probability (CEP)", which is defined as the radius into which a munition can be placed at least half the time, was less than six meters.

The Air Force also wanted a GPS-aided munition based on a heavy penetrator bomb for bunker busting, and so developed a GAM kit for the BLU-113/B 2.1 tonne (4,700 pound) penetrator bomb. The weapon that resulted was originally designated "GAM-113" but later redesignated "GBU-37/B", and the first inert drop of this weapon from a B-2 was in April 1997. It was dropped in combat by B-2s beginning in the fall of 2001, during strikes on terrorist camps in Afghanistan following terrorist attacks on the US.

* As noted, the GAM weapons were strictly an interim development, produced in small quantities at relatively high unit cost, and quickly expended. JDAM was the way of the future, designed to provide the same capabilities as GAM at low cost in high volume, for use on several different aircraft.

The JDAM GPS guidance kit provides a new tail with a GPS-INS guidance system, along with a set of strakes that are strapped around the bomb midbody to control the bomb's fall. The guidance system is programmed by an umbilical connection, though a wireless infrared link is in the works.

Kits are now available for the 900 kilogram (2,000 pound) Mark 84 general purpose or BLU-109/B penetrator bombs, resulting in a weapon with the designation "GBU-31/B", and for the 450 kilogram (1,000 pound) Mark 83 general purpose or BLU-110 penetrator bomb, resulting in the "GBU-32/B". Stated CEP for the JDAM is 13 meters (43 feet), though is likely better than that in practice.

First tests of JDAM were performed in late 1996, and the weapon has been qualified on most US attack aircraft. Production began in 1998 and JDAM was introduced to combat during the 1999 NATO Kosovo campaign, with the B-2 stealth bomber using the weapon to good effect. Kosovo was also the first combat use of the B-2. The USAF also employed JDAMs in 2001, during the campaign against Afghanistan, dropping them from B-52s and B-1s. Post-strike imagery demonstrated the remarkable accuracy of the JDAM, with targeted runways neatly cratered out at all the intersections.

JDAMs also allowed the heavy bombers to fly all-weather close support missions, a role which their original designers could not have imagined. The bombers took off with a load of JDAMs without having specific targets and orbited over the battle area, above cloud cover. If ground forces or spotter aircraft found a target, they reported the target coordinates through an intelligence network, which passed attack instructions and coordinates on to a bomber. The bomber crew loaded the coordinates into the required number of JDAMs, set them for air, surface, or penetrating detonation, proceeded to the target area, and released the bombs.

The goal in this process was a ten-minute "kill cycle", but the Air Force admitted this was difficult to achieve. This was no fault of the JDAM itself, whose accuracy was all that was expected. In addition, Boeing claimed that field use to that time showed the reliability of the JDAM kits to be well above the 98% operability rate required by specification.

JDAM was also extensively used during the US invasion of Iraq in the spring of 2003, making up a substantial portion of the almost 20,000 guided munitions used in the campaign.

The US Air Force, Navy, and Marine Corps originally planned to acquire a total of over 87,000 JDAM kits from Boeing, with total program cost of over $2 billion USD. By the end of 2004, over 100,000 had been produced. The US military has been so enthusiastic about the weapon that their total buy may reach about 250,000, and there has been talk of dropping unguided bombs entirely from the inventory. Unit price for a JDAM kit is about $18,000 USD in 1999 dollars, though original estimates had set it at $40,000 USD.

The success of JDAM in combat led to considerable international interest in the weapon. Israel, Italy, and Australia have adopted it, and Britain is a potential buyer. Boeing believes that foreign sales might reach as high as 60,000, and is working on a license agreement with Matra BAE Dynamics for foreign production.

Boeing funded development of a JDAM kit for the Mark 82 225 kilogram (500 pound) bomb, and the services adopted the weapon, designated "GBU-38/B", finding it useful for attacks in built-up areas where collateral damage had to be minimized. Initial use of the GBU-38/B was in the fall of 2004 during fighting in Iraq. The USAF is using the GBU-38/B to arm B-1 and B-2 bombers, allowing them to drop large clusters of precision weapons in a single sortie, each hitting a separate target. A new smart stores rack was developed for the B-2, allowing the aircraft to carry 80 such munitions. The Japanese Air Self Defense Force is working to obtain the smaller JDAM for its F-2 strike fighter.

* Boeing has evaluated "extended range" version of the JDAM featuring popout "switchblade" wings to provide greater glide distance. Both 225 kilogram (500 pound) and 900 kilogram (2,000 pound) "JDAM-ERs" have been tested; it is unclear if there is any commitment to production but little doubt that they will go into service.

2,000 pound JDAM-ER

Boeing also has considered a version of JDAM based on "compressed" 225 kilogram (500 pound) Mark 82 bombs. Two such shortened Mark 82s could be carried in a bombbay designed to carry a single 900 kilogram (2,000 pound) bomb. The short length would be achieved by using "lattice fins", which are paddle-shaped with a honeycomb lattice of air surfaces inside the paddle. The paddle is faced into the airstream and provides the aerodynamic equivalent of a much larger fin. The Soviets developed the lattice fin concept, and it is in use on several Russian missiles. The Russian Vympel firm holds a US patent on the technology and Boeing pays license fees to Vympel for its use.

Yet another project is a precision terminal guidance seeker with a 3 meter (10 foot) CEP, and the ability to attack moving targets. Boeing is working with the US Navy to test JDAM with an imaging infrared seeker and automatic target recognition. The IIR seeker was developed by the Navy under the "Direct Attack Munition Affordable Seeker (DAMASK)" program. The Navy also has requested that Boeing study other seeker options, such as millimeter-wave radar, SAR, and ladar (laser radar). While such seekers are generally expensive, with a cost of at least $75,000 USD, the Navy and Boeing want to develop new seekers with a much lower pricetag.

Boeing has also developed an auxiliary laser seeker for the JDAM, with the first drops of the "Laser JDAM (LJDAM)" in 2005. A laser seeker is not really a substitute for the advanced seekers the Navy wants, since it can't be used at long range and is hobbled by weather, but it will give precision CEP in clear-weather conditions. Boeing decided to perform development of the laser seeker with company funds in hopes that the US armed services might be willing to buy the finished product, and in fact the Navy and Air Force quickly snapped up LJDAM. The new seekers were refitted to existing 225 kilogram (500 pound) JDAMs, with the upgraded munitions being designated "GBU-54", and seeing combat in Iraq in the summer of 2008.

Interestingly, Boeing says there is no great interest in improving JDAM's resistance to GPS jamming. A Boeing official explains: "JDAM is not GPS guided, it is GPS aided, and the IMU [inertial measurement unit] on there is so good that once it has [target] data transferred from the aircraft, it is extremely accurate with GPS denied." CEP using the IMU is said to be about twice that with GPS assistance, which is a step down but still acceptable for larger munitions, and an advanced terminal seeker may make GPS something that is nice to have but can be done without.

In late 2002, the Air Force also began experiments on attacking moving targets, using JDAMs modified with a datalink to permit course corrections up to weapon impact. There has been further work on this technology, as it provides a relatively cheap option for precision strike. Such a datalink would allow a JDAM with switchblade wings to be dropped from a standoff distance and then guided to target by a battlefield surveillance aircraft, or in potential even a space-based surveillance platform.

* The US has developed upgrade kits to add GPS-INS guidance to EOGBs and LGBs, with the kits installed beginning in the late 1990s. The new GPS-enhanced EOGBs and LGBS were originally designated "EGBU" for "enhanced GBU". For example, a GBU-24/B provided with GPS-INS was referred to as an "EGBU-24/B". However, this was changed to an "E" suffix instead -- for example, a GBU-24B/B LGB became a "GBU-24E/B" GPS-LGB -- though it appears that the old EGBU nomenclature lingers in places.

* On the other side of the Atlantic, the French Sagem company is now developing a set of advanced guided-weapons kits, under the "Armament Air-Sol Modulaire (AASM / Modular Air To Ground Munitions)" program.

The AASM, also known as the "High Agile Modular Munition Extended Range (HAMMER)", was initially available with a GPS-INS guidance system, or an INS system with an imaging infrared terminal guidance seeker, with steering performed by nose fins. The imaging infrared seeker can be programmed with an image of the target before launch to perform pinpoint "fire and forget" attacks on static targets. The tail kit includes popout tailfins and a small rocket booster to increase standoff range, with maximum range being about 75 kilometers (47 miles).

AASM family

AASM entered service in 2007. The French air force, the Armee de l'Air, and the French naval air arm, the Aeronavale, ordered an initial batch of a total of 3,000 kits, with the weapon seeing first combat in Afghanistan in 2008. The AASM was initially carried on French Rafale and Mirage 2000 fighters, with six munitions per aircraft in either case. All six munitions can be dropped simultaneously and are independently targetable. The control system provides the bombs with a high degree of agility. Morocco is interested in the AASM, which would be integrated with the Mirage F1.

The AASM kits were initially being designed for use with French 250 kilogram (550 pound) bombs and US Mark 82 225 kilogram (500 pound) bombs. Kits have been considered for a 150 kilogram (330 pound) variant and for a 1,000 kilogram (2,200 pound) hard-target penetration variant, based on the wedge-nosed CMP1000 bomb core -- though work on a 500 kilogram (1,100 pound) variant has been dropped. The imaging infrared seeker has been upgraded to allow it to pick generic targets from a library, instead of having to be preprogrammed to attack a specific target, with a laser seeker added after that.

A datalink is now in the works, initially with a receiver to obtain course updates and then also with a transmitter to provide a final image of the target before impact. An all-weather millimeter-wave seeker is next on the list. Sagem is promoting AASM to foreign buyers, and would like to leverage the technology to develop long-range glide bombs, antiship weapons, and tactical surface-to-surface weapons.

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[5.5] GPS-GUIDED BOMBS: WCMD / MOAB / SDB / MISCELLANEOUS

* The US has also developed a guided version of the TMD cluster munitions canister family. The "Wind Corrected Munitions Dispenser (WCMD)" or "wickmid", provides INS guidance through the addition of a new tailkit assembly. Unguided cluster bomb units have to be released from low altitude to keep them from being blown off target by the wind. Adding a guidance system permits such munitions to be dropped from high altitude. The original program definition only envisioned an INS tailkit that could provide a CEP of 26 meters (85 feet), which was regarded as acceptable for a wide-area weapon such as a cluster bomb unit, but the tailkit is designed to accommodate a GPS guidance system should such an upgrade seem necessary. WCMD configurations include:

A WCMD with BLU-118 submunitions for power-grid attack has also been introduced, and the Air Force Research Laboratory has developed a new "agent defeat" weapon based on the WCMD named "Stop" to allow it to attack chemical or biological weapon storage facilities using 3,800 titanium flechettes to puncture storage tanks and production facilities. Two of these weapons were expended in the invasion of Iraq in the spring of 2003 under the designation of "Passive Area Weapon (PAW)".

The WCMD kit is now in full production and the weapon been used in combat, with CBU-103/B munitions used in the Afghanistan campaign in the winter of 2001:2002. The United Arab Emirates has purchased a number of the weapons.

The Air Force is now obtaining an "extended range" version of this munition, the "WCMD-ER", which has popout gliding wings to give it a typical range of about 55 kilometers (30 nautical miles) and is fitted with a GPS-guidance upgrade. Initial production is equivalent to the CBU-87, with half of the production carrying a load of 202 CEMs and the other half carrying ten SFWs.

Boeing is working on a new guided cluster munition, the "Counter-Mine System (CMS)", which will use a JDAM guidance system and will dispense a load of 4,000 darts to clear mines out of the target area. Details are sketchy.

* Another US guided weapon that is now being introduced to service is the huge "GBU-43/B Massive Ordnance Air Blast (MOAB)" GPS-guided bomb, intended for attacking caves and similar hard targets. MOAB was developed on a crash basis for use in the US invasion of Iraq in the spring of 2003, but it reached field units too late to see any use in that conflict. Concept studies began in April 2002, with development beginning in September and the first drop 42 days later.

It is a huge weapon, with a weight of 9.84 tonnes (21,700 pounds), 8.48 tonnes (18,700 pounds) of that being explosive in the form of a mix of aluminum powder, RDX, and TNT. It has two long stub wings and four popout lattice-fin tailfins, and is activated by twin nose-mounted fuzes. Its GPS-INS guidance, using a GPS receiver on the tail, allows it to maneuver down narrow valleys, where cave hideouts are often sited to complicate air attack, to impact directly on a cave entrance. The massive shock wave propagates down the tunnel, causing destruction by sheer overpressure deep inside.

MOAB bomb

The MOAB acronym is sometimes said to stand for "Mother Of All Bombs". When the MOAB bomb was announced to the public the city of Moab, Utah, protested against the name, but to no effect.

MOAB is intended for drop by a C-130s, with the guided glide capability allowing the drop aircraft to stand off from the target area. Only a small batch of MOABs was built, but the Air Force sees MOAB as the first of a series of munitions.

The next member of the family, the "Massive Ordnance Penetrator (MOP)", is now being developed by Boeing. It will be a thick-cased weapon with GPS-INS guidance, stub wings, and paddle tailfins, but with a smaller form-factor for carriage on the B-52 and B-2 bombers. It will have a length of 6.35 meters (20 feet 6 inches), a diameter of 80 centimeters (31.5 inches), and a weight of 13.6 tonnes (30,000 pounds), about a sixth of that being explosive filling. When dropped from altitude, it should be able to penetrate 60 meters (200 feet) into the ground and still punch through a reinforced-concrete roof. Development worked slowed for a while, but was then accelerated, with hopes of getting MOP into service by late 2010. The speedup of the program appears to have been based on worries about Iran's nuclear weapons development program, which is built around a distributed network of underground complexes.

* The US Air Force is now acquiring a lightweight GPS-guided bomb, known as the "GBU-39/B Small Diameter Bomb (SDB)", initially known as the "Small Bomb System (SBS)", which in turn was a follow-on to a proof-of-concept effort, the "Miniaturized Munitions Technology Demonstration (MMTD)" program.

The SDB is a penetrating bomb with a weight in the 90 to 112 kilogram (200 to 250 pound) range, and with a length of about two meters (6 feet 6 inches). It has the same penetrating capability as a 900 kilogram (2,000 pound) weapon, but only carries 22 kilograms (50 pounds) of explosive. The SDB was primarily intended for carriage on new stealthy manned and unmanned strike aircraft to allow them to carry weapons internally, while still giving them enough firepower to destroy a number of separate targets in a single sortie. However, of course it can be carried externally, with four SDBs carried on a single multiple ejector rack, replacing a single JDAM; an F-15E Strike Eagle can carry 12 SDBs, all independently targetable. The SDB is also a good store for endurance UAVs like the General Atomics Predator or Reaper, which have small stores loads compared to a strike aircraft like the F-15E.

The SDB incorporates a "differential" GPS guidance system to provide a smaller CEP, and an improved penetrating structure to allow the weapon to pierce up to almost two meters of concrete. Lattice fins are now being considered to reduce size and improve performance.

A "Swing Wing Adapter Kit (SWAK)" was been built for the SDB to allow an aircraft to drop the weapon from standoff ranges of up to 45 kilometers (28 miles) at altitude. If the SDB is being launched at a hard target, the wing will be discarded in midcourse to allow the bomb to build up velocity before striking the target. For soft targets, the wing will be retained until the bomb is in range of small arms fire. Swing wings are envisioned as the default configuration for the SDB.

GBU-39/B SDB

The small size of the SDB is also intended to limit "collateral damage" to nearby civilian structures, and in fact Boeing is working on an improved SDB variant named the "Focused Lethality Munition (FLM)" that will use a composite case and a new explosive filler to produce blast without fragmentation effects, the concept being to destroy a specific target while minimizing damage to the target's surroundings. Drop tests of inert rounds began in 2007.

* The Air Force is very enthusiastic about the SDB. Lockheed Martin and Boeing were selected as finalists, with Boeing winning the award in 2003. The first "all-up" test of live weapons was in late 2004, with two being dropped by an F-15E and both successfully striking their targets. Low-rate production and operational introduction began in 2006, with the munition in combat in Iraq before the year was out. The Air Force plans to obtain an initial stockpile of 44,000 SDBs. The weapon was approved for export to Israel in September 2008, seeing initial combat action against Hamas targets in Gaza at the end of the year. The Israelis would like to obtain a thousand SDBs for starters.

The SDB is fitted with the new "Hard Target Smart Fuze (HTSF)". The HTSF is a tail-mounted fuze that incorporates accelerometers and a processor chip. The HSTF can determine if the bomb has struck earth, concrete, rock, or empty space; can count the number of layers it has penetrated; and can compute distance or time to determine the appropriate detonation time for a specific target.

US weapons designers are also now working on a "Multiple Event Fuze" that could trigger multiple munitions functions, such as igniting a blast-fragmentation warhead to tear open an installation, followed by a fuel-air charge to incinerate it. This implies the use of large combined-effects munitions, but if anyone's working on such weapons, little information has been released on them.

* Even before the SDB entered service, the Air Force began an "SDB II" effort to provide the SDB with a "wide area search / seek and destroy" seeker to hit mobile targets. The seeker was a "triple mode" device, with passive infrared imaging, laser radar, and millimeter wave radar sensors, backup by a target recognition capability and a datalink.

Although the assumption was that Boeing would simply evolve the SDB I design to SDB II, SDB II was set up as an open competition. The Pentagon had found Boeing's performance on the original SDB program outstanding, but a number of defense-procurement scandals -- ironically, several arising at Boeing itself -- meant that a sole-source contract was politically out of the question. Boeing and Lockheed Martin decided to team up to pursue the SDB II contract, being opposed by Raytheon. Raytheon won the contract in 2010, with deliveries of the "GBU-53/B" to begin in 2013 and introduction to service in 2014.

In 2013, the Air Force awarded a contract to Boeing to work on a "laser SDB (LSDB)", with laser seeking terminal guidance; that might seem like a step backwards, but a laser seeker would be far cheaper, and just as useful for clear-weather operations in both day and night. There has also been some interest in a rocket booster to increase standoff range and penetrating power.

* Raytheon is promoting a new GPS-aided smart bomb system for the international market. The company's "Paveway IV" system is essentially Paveway III LGB components, with the laser seeker augmented by a GPS-aided INS, and featuring an innovative "smart" fuzing system that allows the pilot to select airburst, burst on impact, or post-impact time-delay burst before weapon drop. Paveway IV kits can be provided for weapons from 112 to 900 kilograms (250 to 2,000 pounds). The British Royal Air Force has ordered the weapon, though development has been protracted, with fielding now expected in early 2009. The British are interested in follow-on versions, such as a low-collateral-damage munition and a hard-target penetrator.

* Israeli Military Industries (IMI) is also working on a small smart bomb along the lines of the SDB, with adapter kits for 112 and 225 kilogram (250 and 500 pound) bombs. IMI plans to provide a switchblade wing and, eventually, a rocket booster as well.

Rafael of Israel offers the "SPICE (Smart Precise Impact & Cost Effective)" munitions kit, which converts standard dumb bombs ranging from 115 to 900 kilograms (250 to 2,000 pound) dumb bombs into smart weapons. The kit includes fin assemblies and an EO guidance system, with GPS guidance and automatic target recognition; a switchblade wing is optional. The system avionics are based on those of the Popeye standoff weapon, described in a later chapter. A datalink system and booster rocket are being considered.

SPICE guided bomb

The Russians, not to be outdone, have introduced a 500 kilogram (1,100 pound) glide bomb designated the "KAB-500S-E" that can use both GPS and the comparable Russian GLONASS satellite system for guidance. GLONASS-GPS augmentation kits have also been developed for Russian EOGBs and LGBs. They introduced a new family of rocket-boosted glide bombs in 2005, showing off a 1,500 kilogram (3,300 pound) munition designated the "UPAB-1500". Although few details were released, the weapon had popout cruciform wings and cruciform tailfins, and appeared to use EO guidance.

The China Aerospace Science & Technology (CAST) organization has developed an "FT" series of munitions with satellite guidance -- either the US GPS, the Russian GLONASS, or the Chinese domestic Bedou system -- backed up by an INS, with the family including the 500 kilogram (1,100 pound) "FT-1", the 250 kilogram (550 pound) "FT-3", and the 55 to 75 kilogram (120 to 165 pound) "FT-5". With swing-wing kits, FT-1 becomes the "FT-2", while the FT-3 becomes the "FT-6". The Chinese AVIC organization similarly builds 500 kilogram (1,100 pound), 100 kilogram (220 pound), and 50 kilogram (110 pound) variants of its "LS-6" family of laser-guided bombs.

India is currently working on a 450 kilogram (1,000 pound) glide bomb designated the "Extended Range Precision Guided Munition (ER-PGM)", which will feature popout wings and GPS-INS navigation. Accuracy is given as 3 to 4 meters (10 to 13 feet), which implies use of some sort of terminal seeker, and range is given as 100 kilometers (61 miles), which implies a rocket booster. Both general-purpose and penetrating munitions are being considered, as is a gun-launched weapon leveraging off the same technology. Other news reports suggest that India is working on their own series of LGBs as well.

Denel of South Africa has developed a GPS-INS guidance kit for Mark 82 and Mark 83 bombs named "Umbami". The family includes pop-up wing and rocket booster components; the South Africans have also developed and fielded a glide bomb known as the "Raptor", though details are unclear. The Chinese have displayed images of glide bombs with pop-out wing kits and with satellite (GPS/GLONASS) guidance, but have released no details. Interestingly, the Japanese developed an infrared seeker guidance kit designated the "GCS-1" for the 225 kilogram (500 pound) Mark 82 and 340 kilogram (750 pound) M117 bombs. The resulting munitions look much like LGBs but they are "fire and forget" weapons, intended mostly for antiship attack, and do not require a targeting pod.

Diehl of Germany is working on a glide bomb system, using an unusual one-piece pivoting wing instead of the more conventional twin switchblade wings. Two different weapons are under development, one designated HOPE (HOchleistungs PEnetrator / High Power Penetrator) built around a penetrating bomb and another designated HOSBO (HOchleistungs Spreng-BOmbe / High Power Explosive Bomb) capable of being fitted with various modular warheads. Guidance is GPS-INS, but some thought is being given to laser or millimeter-wave terminal attack seekers.

HOPE began initial flight tests in 2008. The baseline HOPE model is in the 1,360 kilogram (3,000 pound) weight range and unusually features a one-piece pivoting wing that can be set to oblique angles to adjust performance. The German Luftwaffe has waffled on obtaining the HOPE-HOSBO weapons family. If a commitment is made, it might be in service by 2012.

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