Deadly accurate

Hikers on the Brecon Beacons might well be used to military jets screaming overhead but, in early July this year, one RAF Harrier had particular significance.

Hikers on the Brecon Beacons might well be used to military jets screaming overhead but, in early July this year, one RAF Harrier had particular significance. At the Aberporth range in south Wales, the first Paveway IV bomb was successfully dropped — a test that could usher in a new era for the UK weapons industry.

Jointly developed by Raytheon Systems in the UK and Raytheon Missile Systems in the US, Paveway IV has been developed to meet the UK’s requirement for a more accurate precision-guided bomb that can help reduce collateral damage. The company hopes that this peculiar thing — a bomb designed to kill fewer people — will one day become the principal UK bomb for the next 20 years.

Raytheon introduced the first Paveway in 1968 in Vietnam, where this original laser-guided bomb revolutionised tactical air-to-ground warfare. Its semi-active laser-guided munitions could home in on targets and not only reduced the number of weapons required to destroy a target, but also provided a level of accuracy, reliability and cost-effectiveness previously unattainable, according to Raytheon. In a later incarnation, Paveway II was used more than any other weapon during the invasion of Iraq with 8,700 dropped, and its ubiquity represented a significant success for UK engineering in the defence sector.

While the key technological change in this latest incarnation is the switch to dual mode — from laser guided alone to a combination of laser guided plus GPS — Paveway IV has an improved capability that goes beyond refinements to its accuracy. The weapon also boasts a ‘height of burst’ sensor, smart fuse as well as increased penetration: all deadly improvements to the original Paveway design. Whereas previous ‘dummy’ fuses simply detonated on impact, the smart fuse — developed by Thales Electronics — enables communication with the bomb, providing greater control over when it detonates.

According to John Michel, head of weapons at Raytheon, this gives the bomb far greater versatility.

‘This provides us with more lethality options. The accuracy of the weapon is all to do with the guidance, whereas the fusing side is controlling when the warhead goes bang, which improves lethality, and if you improve lethality you can drop less bombs,’ he said.

While seemingly cold euphemisms such as ‘lethality’ litter the defence industry, the reduction of collateral damage was actually a key MoD requirement for the new weapon, said Graeme Shaw, Paveway IV’s chief engineer. The desire to minimise the amount of civilian casualties has led to the progressive reduction in warhead poundage from 2,000 to 500. In turn, this reduction in weight has meant that there is now a far greater emphasis on accuracy, according to Shaw.

In Michel’s view, the combination of GPS and laser guidance, together with the height of burst sensor and intelligent fuse is unique, adding a new layer of destructive capability to the device. ‘The height of burst sensor allows it to detonate pre-impact,’ said Michel. ‘You can pre-programme the weapon — depending on the mission — to detonate before hitting the ground or post-impact should you want to go through a structure. It’s a good feature to have.’

The Paveway IV certainly isn’t short of new technology features, nor is the defence industry short of acronyms. The weapon’s accuracy is provided with MEMS IMU (microelectro-mechanical space system inertial measurement unit) that uses a more compact, less expensive system than previous models, while RAPToR (Raytheon Anti-jam Protection Technology Receiver) is said to be the most advanced military GPS available. The bomb also has a SAASM (Selective Availability Anti-Spoofing Module) chip, developed by Raytheon Missile Systems for GPS and anti-jamming.

The warhead itself began life as a conventional Mk 82-shaped weapon. The Mk 82 is a US-designed, unguided, ‘dumb’ bomb that free-falls and is used as a general purpose weapon. However, the Paveway IV warhead was re-designed from scratch to meet penetration requirements by changing the type of steel used, and the thickness ratios around the warhead body were increased to improve the bomb’s ability to withstand impact.

Other requirements demanded that the bomb should be a flexible, inexpensive device that overcame traditional problems such as compatibility. This has been fulfilled by Paveway’s ability to adapt to a number of aircraft, namely the Tornado, Eurofighter and JCA. Under a separate contract Raytheon is also working with BAE Systems to integrate the weapon on to the Harrier platform.

‘This will be the UK’s general purpose bomb for the next 20 years or so,’ said Michel. ‘The US will look to buy hundreds of thousands of GPS bombs and laser-guided bombs, whereas the UK has got one bomb that is extremely flexible and covers all the general scenarios you will have in battle.’

It was not just a desire for more capability and greater accuracy that drove this Paveway evolution. Michel explained that, in a number of conflicts in the early 1990s Balkans war, varying meteorological conditions affected performance to the extent that alternatives had to be found. ‘In Kosovo, the UK was heavily involved but a flaw was discovered in the laser-guided system,’ he said. ‘Operating in clouds the laser energy was obscured and prevented the UK and other countries from carrying out operations. That’s when it was recognised in the UK that it needed GPS-guided bombs.’

But there are also practical and financial benefits to the Paveway IV. The availability of dual mode laser/GPS guidance within a single weapon means that air forces do not have to incur the expense of maintaining two separate weapon stockpiles — another requirement high on the MoD wish list. ‘This was part of the requirement that we set out at the proposal stage and worked upon to meet the MoD demands. That would be a major reason but, from a logistics standpoint, having different weapons in your armoury and trying to manage them is cost-prohibitive,’ said Michel.

Shaw added that — from a military point of view — a more insensitive war head would make it safer operationally to keep in storage; in the event of a fire, less payload makes more sense. Furthermore, more bombs on target reduces the number of sorties to complete the mission and minimises the risk of collateral damage, he claimed.

Developing munitions or equipment for the defence industry is a notoriously laborious and time-consuming process but the development of Paveway IV progressed through a number of distinct stages extremely rapidly. Following the award of the contract for Raytheon, these stages covered design, development and qualification of the weapon before it could finally move into production.

Following its standard product development procedure, Paveway went from preliminary design review at the end of 2004, to critical design review and production readiness — it should be ready to deliver as early as mid-2007. This enabled the company to go from contract award to first use in just two and a half years, an essential attribute to be competitive on the world weapons market, according to Michel. ‘The key is how quickly you can get yours out there,’ he said. ‘These things have a well understood development cycle so we know how long it takes. Raytheon has a good pedigree in terms of performance of its weapons, so for marketing, that is a strong feature.’

The testing in Wales this year was to demonstrate that the new guidance systems and targets had been met. Two more drops are planned, one at the end of this month and the final test at the beginning of October.

There is no getting away from the fact that Paveway IV is a deadly piece of engineering but, for those engineers working on the weapon, the challenges that arise during its development are no different than on any other project. Engine part or laser-guided weapon, the approach is the same.

‘At the end of the day I am a systems engineer,’ said Shaw. ‘And I apply engineering principles to everything I do and follow those processes and principles, so I get the right answer.’