Better bombs make cheaper missiles: in an age when many households have infrared sensors, video cameras, remotely-controlled electronic devices and cars with GPS nagivation, the idea of air forces using simple unguided bombs seems so mid-20th Century. Things are changing.

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The development of add-on guidance and control kits for bombs was motivated by the need to destroy difficult (small, hardened and moving) targets without flying a disproportionately large number of attack sorties, which would tie down a substantial force of aircraft and involve heavy losses. Range-extension kits came later, as air-defence systems improved.

Precision guided bombs made their operational debut on a significant scale in Vietnam in 1972, when the US Air Force had available an EOGB (electro-optical guided bomb) with a 900-kg warhead, and LGBs (laser-guided bombs) with 900- and 1360-kg warheads, providing a CEP (Circular Error Probable) of seven metres.

In 1967 Rockwell had been contracted by the US Air Force to develop an EOGB kit for the 900-kg Mk 84 bomb, resulting in the 1027-kg GBU-8/B Hobos (Homing Bomb System).Work on LGBs had taken off in 1965, with the first successful test of a bomb with laser guidance by Texas Instruments (TI), whose defence electronics business was purchased by Raytheon in 1997. Full-scale development began under the US Air Force's Pave Way (later Paveway) programme, with Texas Instruments contracted to manufacture KMU-342/B guidance kits for 349-kg M117 bombs.

The combination was named Bolt-117 (BOmb, Laser, Terminal guidance-117), and was first used in Vietnam in 1968. By 1972 the M117 with TI kit had been redesignated GBU-1/B Paveway I. Other members of the Paveway I family were the GBU-10/B based on the Mk 84, and the GBU-11/B based on the 1360-kg M118E1.

Over 10,000 Paveway Is were used in Vietnam by the US Air Force alone. The US Navy used only around 1000, due to the cost of jettisoning unused ordnance when returning to carriers.

The Paveway II introduced fold-out fins for improved range and accuracy, and the latest version allows selection of approach heading and impact angle. It has been produced in 225-kg (GBU-12), 450-kg (US Navy GBU-16C/B), 900-kg (GBU-10) and 1360-kg (GBU-11) forms. Up to four GBU-12s can be carried on the US Air Force General Atomics MQ-9 Reaper drone.

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One recent Paveway II development is the GBU-51/B, using the BLU-126/B low collateral damage bomb (LCDB) developed by the US Naval Air Warfare Center (NAWC). It employs a 225-kg class warhead based on the earlier BLU-111/B, but with the mass of the PBXN-109 explosive reduced from 84 to 13 kg, and with compensating inert material added. Deliveries of the BLU-126/B began in March 2006, and over 1500 have now been produced. The GBU-51/B was first used operationally in Iraq in July 2007 from a US Marine Corps Boeing F/A-18D.

As a second source for the series, Lockheed Martin has produced over 40,000 Paveway IIs for the US services and export customers, but most Paveway IIs (over 275,000) have been manufactured by Raytheon.

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Lockheed Martin has been funded by the US Navy to develop and produce a dual-mode version of the GBU-12, adding GPS/INS navigation to legacy Paveway II kits. The bomb navigates toward a preplanned target using GPS/INS, and automatically transitions to laser spot-homing in the terminal phase. Series production of this DMLGB or GBU-12F/B began in August 2007.

Lockheed Martin has developed and manufactures the Laser-Guided Training Round (LGTR). Under a US Navy-funded performance enhancement programme that was completed in 2006 this became the 40.4-kg E-LGTR, which costs only 15% as much as the real weapon. Lockheed Martin has delivered over 50,000 LGTRs to the US Navy and overseas customers.

During Operation Northern Watch in 1998, some Iraqi surface-to-air missile launchers were placed next to mosques and schools and to attack these the US Air Force used 225-kg laser-guided, concrete-filled practice bombs. Possibly inspired by this, the Lockheed Martin Scalpel is a 45.4-kg low-collateral-damage weapon being developed on the basis of the E-LGTR airframe. An inert flight demonstration took place in January 2008 using a new linear seeker and proportional control actuation system. The company is partnered with NAWC under a co-operative research and development agreement to integrate the Scalpel's warhead and fuze by the end of 2008.

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Another Lockheed Martin contribution is the Longshot wing-kit, which can be added to Mk 82/83 bombs, Aerojet/ Honeywell CBU-87/97 Tactical Munition Dispensers and GBU-12/16 LGBs. The Longshot can provide a range of up to 90 km from release at 35,000 ft.

In 2001 Raytheon Systems in the UK commenced production of the GPS/INS-assisted Enhanced Paveway II (EPWII) or BGU-49. The guidance electronics are produced in the UK and final assembly takes place in Tucson, Arizona. The EPWII is to be cleared for 14 aircraft types, including the Eurofighter Typhoon and Lockheed Martin F-35.

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In late 2006, following preliminary retargeting trials in the US against fixed targets, Qinetiq completed Phase I of the UK Ministry of Defence Integrated Sensor to Effect (Ise or S2E) programme to demonstrate in-flight redirection of a modified EPWII attacking a moving target. The main changes were the addition of a Symetrics PC104 improved data modem, a Harris UHF transceiver and two conformal antennas. The datalink operates in both directions, the bomb receiving target data from a ground controller, while the controller receives bomb position and velocity vector data, to assist in battle damage indication (BDI).

The current Phase IA of Ise trials includes redirection of the weapon from another aircraft using WGS84 co-ordinates, and the transmission of still images from a camera in the nose of the EPWII to improve BDI (World Geodetic System 1984, revised in 2004, is the current reference system for GPS).

The Paveway III has even larger wings, and two-stage guidance, with INS preceding terminal homing. The principal variants are the 1065-kg GBU-24 series with Mk 84 bomb or the Lockheed Martin BLU-109/B Advanced Unitary Penetrator, the 987-kg GBU-27/B with BLU-109/B and cropped aerofoils for internal carriage on the Lockheed Martin F-117A, the massive 2130-kg GBU-28B/B (and GPS-assisted EGBU-28) with General Dynamics BLU-113A/B penetrator and the GBU-28C/B with GD's further improved BLU-122/B. The latest Paveway IIIs have selectable approach angles, and time and speed of impact.

It has been claimed (in a US Air Force presentation) that by the time of Desert Storm of 1991, the F-117A could achieve a CEP of 3.05 metres with Paveway bombs, and that by 2004 in releases from the Northrop Grumman B-2A this figure had been reduced to 2.15 metres.

For the British services the EPWII/III is an interim measure, pending availability of the dual-mode RSL Paveway IV, combining laser spot-homing with second-generation GPS/INS guidance, which incorporates anti-spoofing and anti-jamming. It will also have an Enhanced Mk 82 penetration warhead and a Thales/Alliant Techsystems Aurora fuze. The Paveway IV is claimed to have a greater standoff range than any other precision guided bomb, and unique manoeuvrability that allows it to strike a target behind the release point.

While Raytheon Systems is the weapon design authority for the Paveway IV, Raytheon Missile Systems in Arizona is design authority for the warhead and the enhanced computer control group (ECCG). The UK team includes Portsmouth Aviation, EDO MBM Technology and Thales Missile Electronics.

The first deliveries of Paveway IV practice rounds took place in September 2006, with a view to early clearance for the Royal Air Force Harrier GR9/9A operating in Afghanistan. As an interim measure these aircraft have been using the EPWII with the ECCG from the Paveway IV.

Under a contract signed in 2003 it is planned that Raytheon Systems will produce for the RAF over 2000 Paveway IVs. Growth options include the addition of the Lockheed Martin Longshot wing-kit, alternative warheads and a twin-store carrier. Further development may satisfy the shorter-range element of the UK Ministry of Defence Spear (Selective Precision Effects At Range) requirement.

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Russia

Other nations have been inspired by America's Paveway series to develop their own LGBs. Russia's Region produces LGBs in 250-, 500- and 1500-kg sizes under the designations LGB-150, Kab-500L and Kab-1500L. Some observers believe that the Kab-500L inspired China's Lyoyang Lei Ting-2 (LT-2), which was unveiled in late 2006, although it is thought to have entered service three years earlier. Lyoyang is part of Avic-I.

Israel's Elbit Systems manufactures the Lizard LGB series, of which the Lizard 3 was developed to deal with moving targets. After supplying Lizard kits to several export customers, in 2007 Elbit began deliveries to the Israeli Air Force. The new Lizard 4 or Gal (GPS-Aided Lizard) adds GPS/INS. The Lizard's semi-active laser seeker has also been tested successfully on the Northrop Grumman Bat missile for the same company's Hunter drone.

Israel Military Industries produces the 500-kg PB-500A1 penetration warhead, which is marketed in combination with the Paveway II kit. The Missile division of IAI/MBT manufactures the Griffin laser guidance kit, which was reportedly used in attacks on Hezbollah targets in Lebanon in 2006. The company also markets the Next Generation LGB kit for bombs in the Mk 82/83/84 series, offering a twelve-km range and five-metre accuracy.

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TV/IIR

On a small scale, the US Air Force still employs the TV/IIR-guided l125-kg Boeing GBU-15(V) glide bomb, which delivers a Mk 84 or BLU-109 warhead from a range of up to 28 km. Raytheon is responsible for the enhanced version with GPS mid-course guidance, which was introduced in 2001 in Afghanistan.

The addition of a ventral rocket motor turns the GBU-15 into the 1213-kg Boeing AGM-130 missile with Mk 84 warhead or BLU-109.The AGM-130 was first deployed in 1994, and costs around twice as much as the GBU-15. Raytheon has recently been contracted to change the frequency of the datalink (the AXQ-14 datalink pod and ZSW-1 weapon control unit), in line with America's Commercial Spectrum Enhancement Act.

SatNav

Satellite-based navigation, although categorised as only semi-precise, functions regardless of weather and can easily be combined with an inertial navigation system (INS). The leader in GPS/INS weapons is the Boeing Jdam (Joint Direct Attack Munition), which employs a Rockwell Collins GPS receiver and was first used operationally in Kosovo in 1999.

The latest Jdam contract (Lot 12), awarded to Boeing in January 2008, is for 4907 kits at a unit cost of $ 23,560. The company has already produced over 190,000. The Pentagon plans to buy around 217,000 Jdams. International sales were launched with an order from Israel in 2000, since when 18 other nations have been added to the export list.

The main Jdam variants are the 946- to 981-kg GBU-31 series with KMU-556 guidance and Mk 84 warhead or BLU-109/117/119 penetrator, the 468-kg GBU32 with KMU-559 guidance and Mk 83 and the 253-kg GBU-38 with KMU-572 guidance and Mk 82 or BLU-111/126. As noted earlier, the BLU-126/B is the US Navy's LCDB. Saudi Arabia has requested 550 GBU-38s and 350 GBU-31s.

The Jdam kit includes body strakes, which give a range of up to 28 km. The US Air Force quotes a mean accuracy of 30 metres with INS alone, or 13 metres with GPS, against a precisely surveyed aim-point. Five metres may be achieved in tests with optimised GPS signals, but actual operational accuracy is downgraded by errors in specifying target position.

A Jdam version with a terminal seeker is expected to give an operational CEP of three metres. Boeing has private-ventured a laser-augmented development of the GBU-38, named Ljdam and designated GBU-54. It is intended to engage targets moving at up to 112 km/hr, but the corresponding CEP is then doubled to six metres. It is anticipated that laser guidance will also be added to the GBU-31 and -32.

In June 2007 Boeing was awarded a $ 28.8 million initial production contract for 400 Ljdam seekers for the US Air Force and 200 for the US Navy. In full-scale production the laser is expected to add only $15,000 to Jdam unit cost. Israel is expected to be an early customer.

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The Nawc Weapons Division is developing the Damask (Direct Attack Munition Affordable Seeker Kit), aiming for an accuracy comparable to an LGB, but with a launch-and-leave, through-the-weather attack capability. For low cost it employs the Raytheon uncooled imaging-IR camera that was originally developed for the night vision system of the 2000 Cadillac DeVille. It is anticipated that production unit cost will be reduced to around $10,000.

The Damask takes a target 'template' as reference, typically created from satellite or drone imagery or from sensors on the launch aircraft. The Damask-modified Jdam uses GPS/INS mid-course guidance, and at two kilometres from the estimated target position switches on its seeker to correct guidance in the terminal phase.

Under current plans, the Jdam (together with the LGB, DMLGB, LCDB and Maverick) will eventually be replaced in the US Navy inventory under the Direct Attack Moving Target Capability programme, through retrofits to the GBU-12 and -38.

The nature of operations in Afghanistan and Iraq has made range-extension for bombs a low priority. In 2002 a GBU-31 fitted with an MBDA Diamond Back wing-kit was successfully tested from an F-16, but this kit has so far not been ordered for the Jdam.

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Israel Military Industries has conducted preliminary tests of a wing-kit that may extend Jdam range to 80 km. In 2007 tests were carried out in Australia with GBU-38s equipped with wing-kits developed by Hawker de Havilland to meet the RAAF's Air 5425 requirement.

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So far, the effectiveness of any satellite-guided bomb has depended on the Pentagon's willingness to supply the codes that give access to the precise GPS signals, codes that reportedly change monthly. This has discouraged the development of Jdam-competitors, although China's CAIC has developed the 250-kg FF-1 and 500-kg FT-3 as optional armament for the Chengdu FC-1. These presumably use the publicly available version of GPS or Russia's Glonass.

In late 2006 Luoyang unveiled the 540-kg satellite-guided LeiShi-6 (LS-6), which has a wing-kit, and may be linked to Europe's Galileo or China's projected Beidou satellite system.

SDB 

This report has been concerned primarily with add-on kits for existing bombs. However, it is noteworthy that the new 130-kg Boeing GBU-39/B Small Diameter Bomb (SDB-I) has entered US Air Force service with the MBDA Diamond Back wing-kit as standard fit, giving a range of up to 110 km.

The SDB-I entered the US Air Force inventory in October 2006 and was used operationally from an F-15E in the following month. It will later be cleared for the US Navy F-35C and US Air Force Lockheed Martin F-22. 1000 SDBs had been delivered by the end of February 2008. The US services expect to buy 12,000 SDBs at a unit price of around $ 87,000.

The first major development appears to be the 'Focused Lethality Munition' (FLM) or low-collateral-damage version of SDB-I, with a carbon-fibre composite case and a dense inert metal explosive blast warhead containing powdered tungsten. The FLM is intended to provide less than ten per cent probability of serious injury at 30 metres radius. The warhead technology was developed by the Lawrence Livermore National Laboratory and the US Air Force Research Laboratory. Boeing delivered an initial batch of 50 such weapons in early 2008 and the US Air Force is expected to buy up to 450 SDB-1 FLMs by 2012.

The Increment Two (SDB-II) is required to attack moving targets in all weather conditions. It will have a two-way datalink to provide target updates, and a multi-mode seeker that can classify tracked and wheeled vehicles and boats. In the current risk-reduction phase Boeing is teamed with Lockheed Martin (who will provide the seeker) and Harris (datalink) on the GBU-40/B, in competition with a Raytheon project (possibly GBU-50/B). Downselect is expected to take place in late 2009, leading to SDB-II production deliveries in 2014.