Disrupt or be disrupted
Clive Gale looks at how the technology used to build disruptors has evolved since the 1970s, helping bomb disposal experts to work more safely
The improvised explosive device (IED) has become the weapon of choice for insurgents and terrorist groups around the world. IEDs first started to evolve in the 1970s, when they were used in Northern Ireland by the Irish Republican Army (IRA). At the same time, Basque separatists and Palestinian terrorists also began using explosive devices. More recently, they have also been employed by insurgents in Iraq and Afghanistan. With the emergence of al-Qaeda, we have seen a global spread in the use of IEDs.
The modern bomb maker can now access a huge amount of information on the internet, and can source components and ingredients locally in order to make a viable IED cheaply and anonymously. Because of the improvised nature of these devices, wide variations occur between one batch of IEDs and another, and some IEDs have unique characteristics. This means bomb technicians and explosive ordnance disposal (EOD) units constantly need to review their standard operating procedures and equipment to keep pace with the IED threat.
One of the most common techniques used in improvised explosive device disposal (IEDD) is neutralisation via disruption. Disruption is achieved by projecting water or a solid projectile at the target. The objective is to disrupt the device, or a specific component, before it can function as designed. Initially, shotguns and other similar weapons were used for disruption. But their effectiveness was limited, and from the early 1970s onwards, a wide range of water disruptors was developed. These disruptors generally consist of a short barrel that uses an electrically fired impulse cartridge to project water at a high velocity. Water cannot be compressed, is readily available, has a penetrating power and offers relatively low density. It also has a flash-suppressing quality and low chemical reactivity to most explosives.
In an attempt to overcome the considerable weight of larger disruptors, steel is sometimes replaced with titanium – albeit at significantly increased cost – or glass fibre and plastic. To compensate for the increased recoil associated with more powerful loads or lighter barrels, some disruptors expend energy by venting the gases rearwards.
Such disruptors have a peculiar property that can be both an advantage and a disadvantage. Unlike a solid bullet, which retains a constant shape as it travels along and leaves a barrel, liquid leaves the barrel at different speeds. The water that travels the greatest length of barrel leaves the muzzle at a higher velocity than the liquid at the forward end of the barrel when the weapon is fired. This means that, as the column of liquid leaves the muzzle, the parts of the liquid initially closest to the muzzle are overtaken by successively faster increments of liquid and the column of water explodes radially outwards.
This behaviour means the weapon must be fired as close as possible to the target without actually touching it if its penetration is not to be greatly degraded. On the other hand, because the liquid injected through the wall of an IED shoots out radially, it tends to burst the container open rather than simply creating an entry hole and an exit hole and leaving the contents unexposed. As a result, such disruptors are good for thin-walled targets when close-up deployment is possible.
The requirement for accurate aiming at greater stand-off distances has led to the development of longer gun barrels and cartridges pre-loaded with various types of rotating slug designed to fragment upon impact. These are typically made from materials including solid metal and friable mediums loaded with metal dust.
The capabilities of water-projecting disruptors were enormously increased when Sidney Alford, working for the UK Ministry of Defence during the 1970s, had the very simple idea of lining a shaped charge not with conventional metal, but with water, initially casting aqueous jellies on the wall of conical cavities in hollow cones of homemade sheet explosive. The method was quantified and tens of grams of plastic explosive were found to be capable of shooting a jet of water through 20mm of steel. Moreover, since shaped charge jets require several diameters of space to develop completely, they could be used at sufficient stand-off for there to be negligible chance of accidentally disturbing the target. Since shaped charges required no pressure containment to function properly, these new disruptors were very light and required very little support for aiming. Enhancement of performance by containing the projectile water between thin plastic cones took the device from the laboratory to the battlefield. Plastic charges can be transported freely until they are required for use, whereupon a quantity of explosive appropriate to the target can be quickly measured and loaded.
In a variant of this configuration, it was found that the cavity, which could be V-shaped or hemispherical, also worked in the linear equivalent configurations. Moreover, given the fluid nature of water, the cavity in the explosive could be completely filled with water that was still projected as a high velocity jet. The amount of energy imparted to such jets could be considerably enhanced – and the flash largely eliminated – by backing the charge with a water-filled plastic jacket. Such charges were found to scale up and scale down very well, and the larger models could be used to disrupt explosive targets at stand-off distances of up to a metre. Larger models can eject the contents of a car boot or shoot through a car door and eject objects placed inside the vehicle. The smallest models can shoot through a car windscreen and disrupt IEDs placed, for example, on the front seat. The relatively low cost of these devices enabled them to go into service in poor countries, where the IED threat is often more predominant.
The conical charge disruptor used to project water can be used with metal liners to produce much more penetrating jets. Alford realised the particular advantage of magnesium, which makes a jet that ignites as it is formed. This penetrates most conventional explosives without causing detonation and very reliably causes deflagration of the target and complete destruction. Interestingly, when fired through the covering soil or sand into a buried ammonium nitrate-based improvised mine, it also reliably causes detonation.
The IED threat spectrum is broad and terrorists are continually revising their tactics, techniques and procedures. They tend to build increasingly complex devices, occasionally reverting to a more primitive type to fool the opposition. The introduction of craftier emplacement tactics wreaks more human and collateral damage. IED countermeasure technology must always try to stay one step ahead of the terrorists if coalition forces are to successfully mitigate these threats. The range of disruptor technology has increased significantly over the past 10 years in order to meet the evolving IED threat. Reducing the volume of explosive that the charge requires (net explosive quantity) and improving the accuracy of the disruptor tool are important aspects of this development.
Not all manufacturers consider the net explosive quantity (NEQ) of a disruptor charge a priority in the development of disruptor technology, although a lower NEQ assists in reducing the cost of explosives required and reduces the burden of transportation. A lower NEQ does not have to compromise the effectiveness of a charge or the explosive effect, since improved disruptor design achieves the aim with less explosive. The lower NEQ can also mean that the charge body is smaller, thereby reducing the volume of the products for transporting and packing into team equipment.
A disruptor does not have to obliterate the IED in order to perform its task successfully. Today, there is a greater emphasis on forensic evidence to support prosecutions and help investigators to seek out the supply chains. By separating the components through appropriate explosive means, bomb disposal experts are able to ensure that some of the component parts remain intact so that any possible fingerprints can be lifted, brand names or components identified and other forensic evidence obtained. The lower the NEQ and the more accurate the disruptor, the less collateral damage is sustained, so the greater the likelihood of recovering forensic evidence.
In order for governments to be able to select the best equipment to support their bomb disposal operators, they must have a thorough understanding of the type of IED threat. It is paramount for governments and government agencies to receive up-to-date intelligence data. This intelligence will be disseminated into the appropriate areas for capability development and into the procurement chain, enabling the right countermeasure equipment to be procured.
Disruptor technology is evolving to more closely meet the requirements of specific explosive devices. Techniques in the application of explosive engineering have improved the accuracy of disruptor technology along with the efficiency of the explosive loads. These improvements provide the operator with a greater degree of confidence. An operator wants to avoid having to take another shot at the target should the first shot be unsuccessful. Failure to disrupt can cause the device to function, adds critical time to the task and potentially exposes the operator to a greater degree of risk.
Nations are looking for more cost-effective solutions to support their bomb disposal teams and there is a requirement for the industry to deliver solutions. Disruptor technology will continue to evolve as the threat changes and technology advances. Modular and explosively precise disruptors can be used in multiple configurations to suit many different tasks and they deliver a higher success rate. Modular disruptors assist in the management of complex procurement chains, where bulk ordering of fewer products makes it easier for nations to equip their EOD teams in overseas and domestic security operations. With the unrelenting global war on terror, the need for disruptor technology will always remain.
Clive Gale is technical services manager at Alford Technologies. He was in the Royal Navy for 32 years, retiring as a warrant officer clearance diver. He also managed operational Navy explosive ordnance disposal (EOD) teams and was the Royal Navy’s chief EOD instructor at the Defence EOD School