Heavy-handed accuracy: the accurate delivery of aerial bombs has become a cornerstone of modern warfare, combining the desired terminal effects with minimal use of relatively low-cost weapons, and substantially reduced collateral damage and aircrew exposure.

Guided bombs in the form of the command-guided Ruhrstahl SD-1400 Fritz-X and the rocket-powered Henschel Hs293 saw limited operational use with the German Air Force during World War Two. The US Army Air Force used the radio-controlled VB-1 (Vertical Bomb -1) 'Azon' late in that war, while the US Navy employed the TV-guided Interstate TRD-1 Assault Drone and the autonomous ASM-2 Bat glide bomb, which carried an active radar seeker.

At the end of the war the US Army Air Force cancelled most of its guided bomb development (including the infrared-homing VB-6 'Felix'). However, the 450-kg radio-guided VB-3 'Razon' and the much heavier VB-13 'Tarzon', or ASM-A-1, were used in Korea by the US Air Force. The massive Bell Aircraft VB-13 was based on the British 5400-kg Tallboy, fitted with annular wing and tail controls.

True precision came with US Air Force laser-guided bombs (LGB) during the Vietnam War. The Texas Instruments BOLT-117 (BOmb Laser Terminal -117), based on the US Air Force standard 340 kg M117, was evaluated successfully in 1968, but it was decided to place in production the heavier 944 kg GBU-10 Paveway I.

Warheads

Based on recent developments in Iraq, what is needed, notably by the US Air Force, are new warheads to deal with small targets in close proximity to civilian personnel and facilities.

The service is testing a low-collateral-damage warhead with a reduced-density carbon-fibre case. Steel is used only in the base and nose, the latter allowing the case to survive penetration through a 0.3-metre hardened concrete wall. The normal explosive fill is partly replaced by fine tungsten particles, to reduce energy release while maintaining sufficient mass for target penetration. On detonation, the case disintegrates into small non-lethal fibres.

The US Air Force is also developing a Hardened Surface Target Ordnance Package (Hardstop) for use against multi-storey targets and relatively soft bunkers. The Hardstop contains over 50 mini-penetration charges and has a selectable explosion diameter with a minimum range of six metres.

However, mountain caves and deep bunker targets support the continued development of penetrators. Penetration can be improved by increasing mass and impact velocity, by using a more slender shape, by having the warhead impact at 90 degrees to the surface, and (in the context of concrete or masonry) by using a shaped-charge precursor.

The baseline US Air Force penetration warhead is the 874-kg BLU-109/B, developed by Lockheed Martin. It has a diameter of 370 mm, contains 240 kg of PBXN-109 explosive and can penetrate over 1.8 metres of reinforced concrete.

The replacement for the BLU-109 is the 874 kg BLU-116/B AUP (Advanced Unitary Penetrator), developed by the US Air Force Research Laboratory's Munitions Directorate (AFRL-MD). It is similar to the BLU-109 in external dimensions, weight and centre-of-gravity position, in order to simplify application and release clearance. It employs a nickel/ cobalt steel sub-calibre penetrator containing PBXN-109 explosive and housed in an aluminium stabilising shroud. Concrete penetration is virtually doubled to 3.4 metres.

The demands of the 1991 Gulf War led to the development and small-scale production of the 2076-kg General Dynamics Ordnance and Tactical Systems BLU-113A/B penetrator. It contained 270 kg of Tritonal and with a case machined by Ellwood National Forge from surplus 203 mm howitzer barrels.

The 2018 kg General Dynamics BLU-122/B is a further development of the BLU-113, using AFRL-MD steel and newly-developed explosives

for enhanced penetration, fragmentation and blast, in addition to improved insensitive munitions performance. It has an Eglin Steel ES-1 case of 390 mm diameter and AFX-757 explosive, and is intended for use on both the F-15E and the Northrop Grumman B-2A. The principal application for this warhead is the Raytheon GBU-28C/B Paveway III, the original GBU-28B/B version having the BLU-113.

Two-tonne warheads represent a realistic upper weight limit for tactical combat aircraft. However, AFRL has been working on a Massive Ordnance Penetrator, or 'Big BLU', weighing up to 13,600 kg, for use by the Boeing B-52H and the B-2A.

Deeper penetration can be achieved by using a rocket motor to increase impact velocity (which is being researched by Russia and the US), or a nuclear device, which for the US services is currently ruled out by Congressional action. In late 2005 the Bush Administration was forced to withdraw its request for FY2006 funding for a Robust Nuclear Earth Penetrator, primarily due to concern over fallout.

Consideration is now being given to using high-powered microwave devices that generate spikes of electrical energy to disable even the deepest communications and computer equipment.

Another way to attack a mountain cave is to explode a large warhead over the entrance, sending down a shock wave. The Massive Ordnance Air Blast (Moab) is a 9760-kg GPS/INS-guided device with stub wings and lattice tail controls, two nose-mounted fuzes and 8170 kg of explosive. In tests, the Moab has been ejected on a pallet from the rear ramp of a Lockheed Martin MC-130H. Reportedly costing $170,000, it is intended for use from the B-1B, B-2A and B-52H. It might be regarded as a further development of the 6800 kg BLU-82/B 'Daisy Cutter' used in Vietnam and later in Afghanistan.

Fuel-air explosive devices were first used operationally in Vietnam in 1969. These low-cost bombs created a cloud of fuel droplets, detonated to produce a pressure wave. This cleared vegetation and pressure-activated mines from a proposed helicopter site, and also destroyed any buildings and killed any personnel in the area.

The modern thermobaric bomb warhead is a further blast concept development, for detonation underground or inside a building. It employs a special explosive (such as the US Navy PBXIH-135) to produce an extended pressure pulse and high temperatures.

The 900-kg US Air Force BLU-118/B is a BLU-109 penetrator with 255 kg of thermobaric filling and a modified fuzing arrangement. These warheads have been used against cave complexes in Afghanistan since March 2002.

In 2003 there were reports that China was developing a 500-kg thermobaric bomb. Russia is known to market a range of thermobaric weapons.

Dispensers

Submunition dispensers were developed to provide area coverage, compensating for the aiming errors and ballistic dispersion of unguided bombs released from low level. However, when dispensers are released from altitude, wind-related errors make the area covered inadequate. The Lockheed Martin WCMD (Wind-Corrected Munition Dispenser) adds an inertial navigation tail kit to various dispensers, giving an accuracy of 26 metres regardless of weather.

The baseline WCMD is the CBU-103, using the Alliant Techsystems CBU-87 Combined Effects Munition with BLU-97/B bomblets. The CBU-104 is for the Aerojet Ordnance CBU-89 Gator with BLU-91/92 minelets. The CBU-105 is based on the Textron Systems CBU-97 Sensor-Fuzed Weapon (SFW) with BLU-108 submunitions. The CBU-107 Passive Attack Weapon was developed for use against chemical and biological targets, using 3700 non-explosive penetrator rods to minimise agent dispersion. The WCMD-ER is an extended-range development, combining the Lockheed Martin Longshot wing-kit and SFW dispenser. Maximum range is 75 km.

SDB 

The US Air Force needs a small, lightweight bomb with a penetration similar to that of the one-tonne BLU-109. This will allow hard targets to be attacked by lightweight fighters, and more targets to be destroyed in a single sortie.

The initial result is the 130 kg Boeing GBU-39/B Small Diameter Bomb, Increment One (SDB-1), which can penetrate more than 1.8 metres of concrete. The SDB has a Boeing-developed anti-jam GPS/INS guidance system and is carried on a 145-kg Boeing BRU-61/A four-bomb rack. When fitted with an MBDA Diamond Back swing-wing kit it has a range of over 70 km. The combination is now in low-rate initial production and will be deployed on the US Air Force Boeing F-15E in late 2006.

Boeing expects to manufacture around 240,000 SDB-1s (158,000 for the US Air Force and 82,000 for the Navy), all with Diamond Back kits, and 2000 racks. The FY2007 budget request is for 1343 SDB-1s at a cost of $ 99.1 million, indicating an average of $ 74,000. It is anticipated that SDB-1 unit acquisition cost will reduce to $ 30,000.

The US Air Force plans a 'Focused-Lethality Munition' version of the SDB-1, using a composite-case warhead. An initial batch of 50 is being produced under FY2006-2008 funding for tests and operational use. It is to be followed by a batch of at least 450 between FY2009 and 2012.

Increment Two (SDB-2) is to have a two-way datalink and a multi-mode seeker that can classify tracked and wheeled vehicles and boats. In the current 42-month risk-reduction phase, Boeing is teamed with Lockheed Martin on a derivative of SDB-1, to compete with Raytheon, the latter proposing a new airframe that is due to fly in 2008. Boeing has awarded contracts to Harris and Rockwell Collins to produce competing data links for the SDB-2. The sole source SDD (system design and development) phase is to start in late 2009.

The SDB-2 is initially intended for the US Air Force F-15E, and later the US Navy/Lockheed Martin F-35C and US Air Force/Lockheed Martin F-22. These services expect to buy up to 12,000 SDB-2s at a unit price of approximately $ 87,000.

Jdam

The leader in the field of GPS/INS-guided bombs is the Boeing Jdam series, developed to avoid the difficulties encountered in using LGBs in adverse weather during Operation Desert Storm. The Jdam is a guidance and control tail-kit applicable to a variety of bombs, notably the 900-kg GBU-31 series with Mk 84 warhead or BLU-109/117/119 penetrator, the 450-kg GBU-32 with Mk 83 or BLU-110, the 450-kg GBU-35 with BLU-110, and the 225-kg GBU-38 with Mk 82 or BLU-111.

The maximum slant range of the Jdam is around 28 km. US Air Force data refers to an accuracy of 30 metres with INS alone, or 13 metres with GPS, relative to a pre-surveyed aim-point. Boeing is private-venturing the development of a laser-augmented 225-kg Jdam to meet developing US Navy requirements. The laser adds around $ 15,000 to unit cost. Boeing states that production deliveries for the weapon, renamed Ljdam, are planned to begin << as early as 2007 >>.

The US Air Force plans to have 158,000 Jdam kits and the US Navy a fur ther 82,000. Boeing has already produced over 140,000 for the US services and 14 export customers. The FY2007 request is for $ 259 million for 10,661 Jdams, indicating a unit cost of $ 24,300. Around 14,000 Jdams have so far been used.

Paveway

As outlined earlier, the laser spot-homing Paveway I was introduced in Vietnam in 1972, providing accuracy on the order of five metres. Over 56,000 of this first series were produced, and they were still in use in the 1991 Desert Storm operation, when ordnance delivery included 2637 GBU-10A/Bs with Mk 84 warheads and 4493 GBU-12A/Bs with Mk 82s.

The Paveway II introduced foldout tail surfaces, giving improved range and accuracy. For the first time the guidance and control kit was fitted to the US Navy 450-kg Mk 83, producing the GBU-16C/B. The latest Paveway II version gives control over target approach heading and impact angle.

The bombs used in the 7 June 2006 strike by an F-16 to kill Al-Qaeda leader Abu Musab al-Zarqawi were a GBU-12 Paveway II and a GPS-guided GBU-38 Jdam. The target was illuminated by a Northrop Grumman Litening flir and laser-designator pod. The lightweight GBU-12 and GBU-38 are also cleared for use on two US Air Force General Atomics YQM-9A Predator Bs deployed in southwest Asia.

The Paveway III has even larger 'wings', giving significantly better range, especially from low level, and requiring two-stage guidance with INS preceding laser homing. The principal variants are the 1065-kg GBU-24 series with Mk 84 or BLU-109, the 985-kg GBU-27 with the BLU-109, and the 2130-kg GBU-28 with BLU-113. In the case of the latest GBU-24s it is possible to select time and speed of impact and azimuth and elevation approach angles.

Following adverse weather experience with LGBs in Kosovo in 1999 Britain ordered the Raytheon Systems (RSL) GPS-assisted Enhanced Paveway II/III (EP2/3). A team led by Qinetiq has successfully demonstrated a datalink for the EP2, allowing changes of target coordinates during bomb flight. Raytheon's Enhanced Paveway is described as the only fully developed, combat-proven dual-mode weapon system that is in production today.

The EP2/3s are interim measures for the UK, pending availability of the similarly GPS-assisted RSL Paveway IV, which is to enter service on RAF Harriers in mid-2007. The Paveway IV employs a new Lockheed Martin-designed 227 kg warhead produced by SEI and a Thales hard target fuze. RSL is to produce over 2000 Paveway IVs for the RAF and is offering it as an upgrade for Saudi Tornadoes. Growth options include the addition of the Lockheed Martin Long-Shot wing kit.

Over 250,000 Paveway bombs have been produced for the US and 35 other nations. More than 40,000 have been used in combat, including about 8700 during the invasion of Iraq in 2003. Most have been produced by Raytheon, but Lock heed Martin designed and makes the Laser-Guided Training Round, and has manufactured some of the GBU-10, -12 and -16 Paveway II series.

The latter company has been funded by the US Navy to develop and produce a dual-mode (DM) version of the 225-kg GBU-12 Paveway II, adding GPS/INS navigation to legacy Paveway II kits. Meeting a US Marine Corps requirement, this will allow the weight-critical Boeing AV-8B to fly a longer patrol in a low-demand environment, carrying only two DMLGBs, rather than the current load of two GPS-guided Jdams and two laser-guided Paveways.

The Paveway has inspired LGB developments in other countries. Russia's Region markets LGBs in 250 kg, 500 kg, and 1500 kg sizes (LGB-250, KAB-500L and KAB-1500L). The KAB-500Kr and -1500Kr are TV-guided, and the new KAB-500S-E is satellite-guided, using Glonass/GPS. Bazalt offers a Fab500M62 with MPK wing-kit and 'correction module'.

Israel's Elbit Systems manufactures its Lizard LGB series. The Lizard 3 was developed to deal with moving targets, and the new Lizard 4 adds GPS/INS. Israel Military Industries produces the 500-kg PB-500A1 penetration LGB, and in 2003 unveiled the 1000-kg class M-2000 warhead. Rafael manufactures the Spice 2000 bomb, based on the Mk 84, but with IIR/CCD seeker and large fixed aerofoil surfaces.The Spice 1000 is a later development based on the Mk 83, with a swing-wing kit for longer (60 km) range and to suit internal carriage. It has an IIR/CCD seeker with automatic target recognition facility and INS/GPS midcourse guidance.

The trend to modular weapons is illustrated by the 340-kg Sagem Defense Securite AASM (Armement Air-Sol Modulaire), based on a 250-kg bomb. The nose-mounted guidance kit provides INS/GPS in the baseline version, but an IIR seeker will be available later. The tail-mounted range-extension kit has four large fins and can contain a rocket motor. A wing kit may be added later.

South Africa's Denel Umbani (Lightning) project follows earlier experience with the Raptor glide bomb and will combine the Mk 82 or Mk 83 bomb bodies with a rocket motor, a swing-wing and a choice of guidance systems. Reports indicate that Denel is seeking a foreign partner to share development costs. The Umbani is aimed at use on the SAAF Gripen.

The Diehl/BGT Defence Hope and Hosbo are technology demonstrators funded by the German Government to provide a basis for emerging German Air Force requirements. The Hosbo is a glide bomb with multiple warhead options, including an HPM device. The Hope is evidently rocket-powered, with a penetration warhead. Both employ variable-sweep oblique wings, giving a range of 50 to 100 km.