Thermobaric weapons on the battlefield

Thermobaric weapons, sometimes also referred to as ‘enhanced blast weapons’ or ‘vacuum bombs’, and their common subset fuel-air explosives (FAE), have been used in various conventional weapons used by militaries and even improvised explosive devices (IEDs) used by non-state actors. These weapons are said to have been used in Afghanistan, the Middle East in different locations, including the Syrian Civil War, in the current conflict in Ukraine, and even in a terrorist attack in Bali, Indonesia.

There are a number of different names for this category of weapons and their notoriety has only grown in recent years as their combat use has become more visible thanks to the 24-hour news cycle and social media. Fundamentally all of these different names encompass weapons with fundamentally similar operating characteristics. Once these characteristics are understood, the mechanics of making such weapons are actually not that complicated. Hence the ability of non-state actors to potentially deploy large-scale improvised explosive devices (IEDs) whose destructive effect is greatly enhanced compared to more commonplace IED devices.

The first use of a fuel-air explosive (FAE)-type weapon was in 1967 in Vietnam, when the US Marine Corps (USMC) were investigating a new way of clearing minefields; this consisted of a canister containing ethylene oxide. The canister was set to initiate at a pre-planned height, which would release a vapour cloud of ethylene oxide that was then ignited, producing an explosion with extremely high overpressure that would lead to the detonation of the mines in the target area.

Vapour cloud explosions occur outside of the military sphere, hence there is a lot of knowledge of the phenomenon. Typical examples include coal and grain dust explosions, the dust combines with oxygen and a spark can set off an explosion. Understanding vapour cloud explosions led to an effort to weaponise this phenomenon. Work towards this end took place at the US Naval Air Weapons Station China Lake, resulting in the development of a cluster munition that was tested operationally in South Vietnam in 1971/1972. This brought about the CBU-55 which contained three BLU-73A/B submunitions – it was the CBU-55 that would demonstrate the effectiveness of FAE munitions.

In April 1975, the Vietnam War was reaching its conclusion as the North Vietnamese Army (PAVN) successfully invaded South Vietnam, whose military proved incapable of extended resistance. However, at the town of Xuan Loc, southeast of Saigon, the 18th Division of the South Vietnamese Army (ARVN) did demonstrate successful resistance at one stage, confronting four PAVN divisions. To support the ARVN effort at Xuan Loc, the US military delivered a single CBU-55 system for use by the South Vietnamese Air Force (RVNAF).

On 21 April 1975, a C-130 Hercules transport took off carrying a CBU-55 on a pallet, at an altitude of 6,098 m the pallet was pushed out of the rear ramp of the transport aircraft, targeted at an area where PAVN forces were thought to be. The CBU-55 then released its submunition payload at the pre-set height, which created a vapour cloud of propylene oxide which was then ignited. An RVNAF photo-reconnaissance mission over the target area soon after the CBU-55 attack revealed that 250 PAVN troops were casualties (a significant proportion of a PAVN infantry battalion), primary caused by the ignition of the vapour cloud denuding the area of oxygen.

The US military developed a further FAE system in the form of the CBU-72; this contained three BLU-73/B submunitions, each containing some 34 kg of ethylene oxide creating a vapour cloud some 18 m in diameter and 2.43 m thick. The CBU-72 was also used by USMC Aviation in Operation Desert Storm in January/February 1991, with some 250 weapons being dropped. Subsequently, the US withdrew its FAE CBUs from service during the 1990s.

Soviet and Russian solutions

Operational usage of FAE systems proved their effectiveness, while other weapon systems could generate similar levels of lethality, the reputation that FAE systems had gained far outweighed that of these other weapon systems. The potential usage of FAE systems had significant morale effects on hostile forces. There were also efforts to portray FAE and thermobaric weapons as uniquely dangerous and in 1980 there was an unsuccessful effort to have them banned by the United Nations. By that point these weapons were already starting to proliferate, with numerous nations starting to field such weapons or seek to develop capabilities in this area.

The Soviet military had become enthusiastic in supporting the development of thermobaric/FAE systems, initially by fielding air weapons in terms of a FAE bomb system. Developments continued by 1988 a prototype of the TOS-1 ‘heavy flamethrower system’ was deployed to Afghanistan for evaluation under combat conditions. TOS-1 is a 220 mm calibre multiple rocket launcher (MRL) system based on a T-72 tank platform. The 220 mm rockets initially had a maximum range of some 3 km and were equipped with thermobaric warheads, this short engagement range necessitated that the launch vehicle had significant protection features, hence the decision to mount the system on a T-72 platform. The TOS-1 was used by Soviet forces in Afghanistan in both 1988 and 1989, with satisfactory results being obtained, paving the way for the system to be fielded in significant numbers.

The problem was that the TOS-1 emerged just as the Soviet Union was starting to implode, the ongoing political dislocation impacted both the Soviet military and defence industry. Matters came to a head on 26 December 1991 with the official end of the Soviet era and the emergence of the new Russian state. Achieving political and economic stability would take time, gradually this was achieved, allowing the Russian military and defence industry to become properly established. The conflicts in Chechnya from the mid-1990s to the eventual withdrawal of Russian troops in 2009 (the first and second Chechen Wars) did lead to military innovation in Russia, and as the economic situation improved new weapon systems could be fielded.

Thermobaric proliferation

Russia would deploy an increasing array of thermobaric weapons for both air and ground forces. In terms of air weapons, options include: S-8D/S-13D 80 mm/122 mm air-to-ground rockets, ODAB-500PM/PMV FAE bombs, ODAB-1500 FAE bomb, KAB-500KrOD guided bomb, KAB-1500 guided bomb and ODS-OD cluster bomb unit with eight FAE submunitions. In 2007, Russia tested the largest thermobaric weapon to date, the so called ‘Father of All Bombs’ (FOAB), with the test officially disclosed on 11 September 2007. Available data gives the bomb a weight of 7,100 kg, a blast radius of some 300 m and a blast effect equivalent to 44 tonnes of TNT. When the FOAB test was publicised, the Russian authorities noted that the weapon was the most powerful thermobaric bomb of its kind and that its blast effects would be equivalent to those of a (small) nuclear weapon, albeit without the post-detonation effects of a nuclear weapon.

We have already mentioned the TOS-1 MLRS system, additionally the 9K58 Smerch MLRS system also has a thermobaric option in terms of the 9M55S 300 mm rocket. The latest 9A52-4 Tornado MLRS system can use the 9M55S rocket, as well as the newer 9M529 rocket with a thermobaric warhead that can reach a range of out to 90 km.

Russia led the way in applying thermobaric warheads to infantry weapons, one of the earliest developments in this regards was the RPO-A Shmel, a 93 mm calibre rocket launcher sighted out to 600 m, the upgraded RPO-M Shmel-M is sighted out to 800 m, although in both cases effective range is much less. The Shmel replaced the earlier RPO-Rys’ system, the rocket in this system had an incendiary warhead rather than the thermobaric warhead of the Shmel.

The RPG-7 has been provided with a thermobaric grenade in the form of the TPG-7V, while the RPG-29 has the thermobaric TBG-29V grenade, with the RPG-32 having the thermobaric TBG-32V grenade. One-shot anti-tank weapons have also been produced with a thermobaric option, such as the RPG-26 Aglen-2 with the RShG-2 round and the RPG-27 loaded with the RShG-1 round.

The number of different of Russian portable weapons with thermobaric capabilities has made their proliferation likely, as many of the aforementioned weapons have been exported. The diversity of these weapons has also demonstrated that producing weapons of this nature is not as challenging as many had anticipated, creating another source of proliferation for weapons in this category. Nations said to have developed thermobaric weapons include Brazil, India, Republic of Korea, Serbia, Spain and Ukraine, amongst others. China has also developed thermobaric systems ranging from a weapon in the Shmel-A category, to 300 mm artillery rockets and mine-clearance systems utilising FAE effects. North Korea has developed thermobaric artillery rockets, reportedly so has Iran, and these are said to have been supplied to their non-state actor surrogates around the Middle East.

Current situation

Although the US can be considered to have led the move towards FAE/thermobaric weapons, this article’s description of more recent events in this sector by Russia and others would seem to indicate that the US has lost interest in this area. That is not precisely true, although they do not have the wide spectrum of FAE/thermobaric weapons available to Russia, for example, they do have capabilities in this area, for example the AGM-114N Hellfire missile with its Metal Augmented Charge (MAC) warhead, a clever change of taxonomy for what is really a thermobaric warhead.

In May 2018, the UK Ministry of Defence (MOD) responded to a Freedom of Information (FOI) request and allegedly released by mistake detailed information on Royal Air Force (RAF) MQ-9 Reaper UAV operations over Syria against Islamic State forces in the previous three months, disclosing that 63 AGM-114 Hellfire missiles had been fired, of which 19 were the AGM-114N4 variant with the MAC warhead. Prior to that, some years earlier, the MOD had released information that the British Army’s Army Air Corps AH1 Apache attack helicopters in anti-Taliban operations in Afghanistan had launched 20 AGM-114N missiles in 2008 and 20 AGM-114N in 2009. Apart from the US military, the Royal Australian Navy (RAN) has purchased the AGM-114N for use from its MH-60R helicopters. Other export customers include Iraq.

Another US effort in the thermobaric area saw the development of a rocket for the USMC Mk 153 shoulder-launched multipurpose assault weapon (SMAW). This led to the Mk 80 Mod 0 Encased Novel Explosive (SMAW-NE) rocket being developed in response to a USMC Urgent Operational Requirement (UOR) to have a new rocket to support urban combat operations in Iraq. SMAW-NE was used in both the First and Second Battles of Fallujah in Iraq in 2004. The US has transferred a number of SMAW systems to Ukraine Ground Forces in early 2023, there is no information of whether SMAW-NE rockets were supplied in addition to standard SMAW rocket natures.

Apart from the RAF, other nations have used thermobaric weapons over Syria, with considerably less discretion than the British. The Syrian regime has not been shy of using its own airpower against civilian anti-regime targets. They were accused of using ODAB-500PMV FAE bombs in attacks against cities, such as Aleppo in 2012, and Al-Qusayr in western Syria in 2013; the use of FAE bombs against civilian targets in Syria has continued since then. International condemnation of the Syrian regime for using FAE bombs against civilian targets has never been sustained, hence the continuation of such attacks.

For the Russian military, the use of thermobaric weapons such as the TOS-1 were seen as giving them the capability to re-capture the Chechen capital of Grozny in early 2000, without the casualties that would have been incurred with a conventional assault on an urban centre. Unsurprisingly, the successor TOS-1A and other Russian thermobaric weapons have been used in combat since the invasion of Ukraine in February 2022. Ukraine has responded though, with systems such as RGT-27S/S2 hand grenades, these are thermobaric weapons, which have also been used as the payload for drone attacks on Russian armoured vehicles and fortified positions.

The use of thermobaric/FAE weapons is not as controversial as it once was, even though the combat use of such weapons has become much more common. Most likely it will take sustained urban combat under the full gaze of the international media, the visible use of thermobaric/FAE weapons and substantial civilian casualties to restart efforts to ban such weapons. In the meantime, they will continue to be used around the globe as they provide a unique operational capability.

David Saw