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What are Improvised Explosive Devices?

The UN International Ammunition Technical Guideline has an IED as ‘a device placed or fabricated in an improvised manner, incorporating destructive, lethal, noxious, pyrotechnic or incendiary chemicals and designed to destroy, incapacitate, harass or distract. It may incorporate military stores, but is normally devised from non-military components’.[1]

The United Nations Assistance Mission in Afghanistan describes it as ‘a bomb constructed and deployed in ways other than in conventional military action’.[2]

While the US Department of Homeland Security lists them as ‘bombs that are constructed in part or wholly from military or commercial explosives or commercial components, and used in a manner other than intended by the manufacturer’.[3]

These are just some of the attempts to encapsulate what has become the most lethal explosive weapon in use today. And yet, while the term Improvised Explosive Device (IED) typically conjures up images of military vehicles being attacked by roadside devices in various insurgent propaganda videos, their use is much wider and more varied than this singular use might suggest.

Probably the key unifying element is that an IED is rarely, if ever, produced by traditional manufacturing processes with a rigid mode of employment. The key to them is their ‘improvised’ nature – one that will utilize available materials in order to attack an opponent. An explosive charge might, in such a way, be constructed from commonly available chemicals, but it may also include conventional munitions (such as artillery shells adapted as roadside bombs).

IEDs are certainly not a new phenomenon, with records of IED use over the last 500 years. But they continue to evolve in their design, based around available materials and the use to which they are put. And their popularity in the hands of non-State actors is a growing concern in dozens of countries around the world.

There are a number of ways in which best to categorise IEDs. Perhaps one of the better ways is to define them by the mode by which they are initiated. If we follow this (commonly used) categorization we can see the following:

  1. Timed IEDs: here the IED is initiated by some form of timing mechanism, set by the perpetrator so that they can remove themselves from the scene. The timing mechanisms might be a burning fuze, a mechanical time or an electrical timer.
  2. Command initiated IED: this is when the IED is initiated at the moment the terrorist decides. The initiation might be by command wire, by radio control or as a suicide switch. Thus the terrorist can initiate the device as a target presents itself.
  3. Victim operated IED: this is when the IED is set by the perpetrator so that an unknowing act by the victim causes the device to function, so the perpetrator does not need to be present. The mechanism might be a trip wire or a pressure pad for instance

Clearly there are many variations within each of these categories, but in general terms almost all IEDs fall within these three main areas. And, in essence, recent developments have not changes these fundamentals.

Typically, IEDs have four key components: a main charge of explosives; an explosive initiator (a small amount of energetic explosives); a switching mechanism; and a container of some sort. Most developments in IED design and construction involve one or more of these.

Recent developments in the design of IEDs have focused on a number of areas, namely:

  1. Explosive component design (for instance to provide better target effects and become more lethal). Here, the main charge and the container in which it is contained is changed or developed.
  2. Explosive component precursors (for instance the use of commonly available precursors to make explosives.) Here the main charge is developed. In some cases alternate explosive initiators have been developed.
  3. Design of projected IEDs such as improvised mortars and rockets, to extend range and effect. Here a range of aspects including the container and other components have been developed.
  4. Device concealment to better hide the presence of an IED. Here the container is developed to conceal the device better.
  5. Command initiation developments, typically to utilise modern radio technology. Here the switching mechanism is developed.
  6. Sensor initiation developments, typically to utilize modern sensors to initiate victim operated devices. Again this is a switching mechanism development. Some developments in IEDs however have seen a regression use of technology – old, well known technology (such as the use of two saw blades set in parallel which form a circuit when they touch due to the pressure of a foot continually recycle over the ages.

This paper will discuss each of these in turn, in particular highlighting the “drivers” that led to these developments, and which perhaps give an indication of future trends.

Explosive component design
Perpetrators of IED attacks are faced with a range of targets and naturally those targets may take measures to improve their protection from the effects of an IED. This leads, naturally, to the perpetrator considering ways in which to improve the effect of the explosive component in order to overcome those defensive measures. At the simplest level this might simply be the use of larger quantities of explosives. In the 1970s, a car bomb or VBIED might typically contain explosives within a container such as a barrel or a suitcase loaded in to the trunk of the vehicle, because targets of VBIEDs were not protected. Today, with a greater awareness and presence of the VBIED threat, defences include protected facilities or greater “stand-off” achieved by security measures. Over the last few years we have seen larger and larger VBIEDs in a variety of countries around the world as security protocols keeping vehicles further from the VBIED targets increase.

A second form of development of explosive component design is the use of more sophisticated explosive component design. When faced with armoured targets some terrorist groups using IEDs have used the physics of explosive component design to develop the design of the warhead to create more penetrative effects from their IED, using shaped charges for instance. Shaped charges come in a variety of configurations, from high angle cones to dishes, all of which are deformed by the somewhat complex interaction of the explosive blast wave into a range of penetrative effects. These effects can be further developed by use of a range of different metals which deform in different ways.

Explosive component precursors
In many circumstances, perpetrators of IED attacks do not have access to military explosives. In these circumstances those constructing IEDs must develop their own explosives. Typically this has been by utilising a mix of an “oxidser” and a “fuel” in appropriate portions which one might consider as precursor chemicals. The chemistry of an oxidising reaction is such that in the right proportions and with the right level of mixing, the reaction becomes explosive when appropriately initiated. Over the past few decades one of the most common explosive mixes has been Fuel Oil (fuel) and Ammonium Nitrate (oxidizer), commonly called ANFO. However, a very wide range of different fuels are possible and they need not be carbon based – so some recent developments have been the use of a range of differing fuels and oxidisers, driven often by the availability of material (if, for instance Ammonium Nitrate is made difficult to obtain by security legislation). Sometimes, albeit rarely, the explosive mix might be chosen to provide a slightly different effect, such as Ammonium Nitrate and Aluminium powder (the fuel in this case) which has a shorter peak pressure than ANFO – more likely to “crack” concrete then perhaps “lift and throw” it. But there may be other reasons for this development – ANFO mixes separate out over time as the liquid fuel oil moves to the bottom of the container causing less than perfect mixing – but an Aluminium powder and Ammonium Nitrate mix separates much less over time. The range of possible fuels and oxidisers is quite significant and some developments have seen the use of innovative precursor materials.

In other circumstances, rather than create a mix of fuels and oxidisers some IED constructors have developed explosive compounds – a single chemical material that is explosive when it decomposes. Such explosives were effectively first “discovered” in the 19th century with the work of Nobel to develop Nitroglycerine and subsequently others to develop TNT. While theoretically todays IED user could produce such material, very often they use easier-to-obtain precursors such as Hydrogen peroxide and acetone to produce TATP, a particularly sensitive explosive. TATP has been used in devices as a main charge, but is also energetic and sensitive enough to be used as an initiator.

Design of projected IEDs such as improvised mortars and rockets, to extend range and effect.
IEDs such as improvised mortars and rockets have been around for decades, and perhaps centuries. In a number of places, they are still being developed, typically to extend range or payload.

Device concealment to better hide the presence of an IED.
In recent years there have been some significant developments to conceal IEDs so that they may pass a variety of forms of security screening. Devices have been built in to the body of a vehicle, into shoes, to hide them during pre-flight aviation security, and in one incident built into a complex piece of equipment (a printer) to allow it to be loaded on an aircraft. In truth, concealing devices is not new but IED users are continuing to show innovative developments in this regard.

Command initiation developments, typically to utilise modern radio technology.
Makers of IEDs have always used radio initiation systems to remove themselves from the site of a bomb location ever since radios were invented. And ever since “jammers” were deployed by those defending against such attacks, terrorists have explore ways of getting around such defences, either by moving the frequency of the command system to an area of spectrum outside the jammer’s capability or using a combination of switches (such as a radio control signal to turn on a sensor before a vehicles jammer affects the radio signal, allowing the sensor to trigger the device.) Fundamentally, the radio control system is no more than a switch, but a switch that many nations have now spent billions of dollars to defeat.

Sensor initiation developments, typically to utilize modern sensors to initiate victim operated devices.
IED designers will use a variety of ingenious mechanisms for victim operated switching. Sometimes these will use the latest technology, such as IR heat sensors, but at the other end of the spectrum mechanical booby trap pull switches or pressure plates are constantly recycling, and may appear to be a “development” in one operational theatre or other.  

How are IEDs employed?
The ways in which IEDs are employed are as diverse as the methods of construction. While IEDs are certainly used as a tactical weapon to defeat personnel and vehicles, they also play an important role at the strategic level of warfare. As Michael D. Barbero, Lieutenant General, U.S. Army Director JIEDDO, has succinctly said: ‘The IED is a weapon used strategically to cause casualties, create the perception of insecurity, and influence national will.’[4] A current example of the use of IEDs as weapons of both tactical and strategic use is the use of IEDs – both suicide-initiated and otherwise, by the so-called Islamic State.

Offensive operations
At the tactical level, Iraqi Ba’atthist doctrines of superior firepower at the outset of attacks have been adopted by Islamic State in its more conventional (ground holding) military operations.[5] However, as sufficient resources of armour and artillery are in short supply, they have adapted to using SVBIEDs in place of conventional military equipment to achieve the same aim.[6] In their attack on Ramadi in May 2015, for example, IS used up to 30 car bombs to overwhelm static military defenses in advance of an infantry attack.[7] In the same offensive campaign, IS also used roadside IEDs to block roads in order to cut off the city from reinforcements – again showing their ability to use improvised weapons for conventional fighting.[8] Another important example of the use of IEDs as a tactic in offensive operations was the Abu Ghraib prison break on 21 July 2013, where the use of SVBIEDs led the way for an infantry assault which resulted in the escape of over 500 prisoners, bolstering the numbers of al-Qaeda in Iraq, Islamic State’s predecessor.[9]

Suicide bombings
The use of suicide bombings on civilian targets is an important aspect of IS’ broader strategic aims, Fermenting sectarian conflict is a key goal of IS in order to create the perception of insecurity as well as to incite Shi’a attacks on Sunni civilians as retribution, thereby pushing Sunnis into the hands of a group who claims they can protect them, namely IS themselves. Although not a suicide attack, the use of timer-operated IEDs by al-Qaeda in Iraq destroyed one of Shi’a Islam’s most holy sites – the Askariya shrine in Samarra – in February 2006.[10] Despite calls for restraint by Iraq’s Shi’a spiritual leaders,[11] retaliatory violence killed at least 15 people, including three Sunni Imams, and 27 Sunni mosques were destroyed on the day after the attacks,[12] with the total in the month following the attack possibly as high as 3000 killed.[13] Again this shows that IEDs are a strategic weapon, and can be used for deadly effect even when the blast doesn’t result in any casualties.[14]

Defensive operations
IEDs also play an important role in the defense of IS held territory at the tactical level. For example, during the YPG’s assault on Hassaka neighborhood of al-Zuhur, Islamic State fighters placed IEDs to slow the Kurdish advance, showing their adaptability in using improvised weapons as a tactic of a conventional fighting force.[15]

At a strategic level, while they may be struggling to hold ground in recent months, the extensive placement of IEDs can prevent or delay post-conflict stabilization of areas they formerly held, and so disguise their basic numerical inferiority.[16] This “economy of force” strategy is, according to Michael Knights and Alexandre Mello of the Washington Institute for Near East Policy, an under-acknowledged capability of the Islamic State, and this “slow burn” strategy is “where its real strength lies.”[17] This underlines the importance of the use of IEDs to Islamic State’s broader strategy.







[5] Central Intelligence Agency reports on Iraqi tactics noted that assaults were “preceded by artillery barrages” and that “the Iraqis learned to rely heavily upon armored units for offensive operations. By 1984, tank formations were almost always used for the primary assault.”

[6] Ibid.











[17] Ibid.