This article was written by guest writer Helvegen and edited by Jeff.
Ever since infantry learned to hide in fortifications and buildings, getting them out of those has been an ongoing issue. The fighting on the western front of the first world war makes for a great example on that subject, here field fortifications were ubiquitous and assaulting infantry lacked the direct fire capabilities to defeat such obstacles. The need for anti-fortification firepower was so great that soldiers in the field had to come up with many improvised means to overcome them.
Some of the means of enhancing the anti-fortification potential of infantry were through the creation of improvised explosive charges for use against dugouts, an example of such an adaptation was the Stokes 81mm mortar shells were being repurposed as “heavy” hand grenades, or the more famous German “Geballte Ladung” grenade, made by strapping 6 stick grenade charges to each other, resulting in a much more potent blast, effective both against structures and vehicles.
The Great War also saw the birth of the flamethrower, a weapon designed to fire streams of burning liquid which had devastating effect against entrenched positions and their occupants. These did, however, come with many drawbacks including a short range, very noticeable light emission, and the overall weight of the system itself. All these factors combined to limit their overall usefulness. In the 1970s some attempts were made to fix the shortcomings of the flamethrower. Among these was the USA’s M202 FLASH and Soviet RPO Rys, which instead of firing a pressurised stream of flammable liquid, fired a rocket with similar incendiary compounds that would ignite on contact with its target. The extended range of the system and the change in the delivery method greatly increased the system’s range and user safety compared to traditional flamethrowers.
Following the adoption of the RPO Rys, the USSR began the development of a replacement. This was the RPO series of disposable launchers, included in 3 different variants:
- The RPO-Z: incendiary rocket launcher
- The RPO-D: smoke rocket launcher
- The RPO-A: thermobaric rocket launcher
The RPO-A, nicknamed “Shmel”, is a single use disposable 93mm thermobaric launcher, which weighs 12 kg and uses a payload consisting of an RDX central charge inside a canister filled with the OM-100MI explosive compound, made of isopropyl nitrate (IPN) mixed with aluminium and magnesium powder.
When the thermobaric warhead impacts, the central RDX charge detonates, dispersing the OM-100MI fuel and metal particles into the air. The cloud of thermobaric mixtures is then ignited, creating a prolonged blast wave with lower peak pressure compared to conventional explosives, but with a much longer duration and an extended “negative pressure” phase, greatly increasing its lethal effect on personnel, both in the open and in entrenched positions, but also in some circumstances its destructiveness against structures.
The RPO-A has been used with great effectiveness since the late 80s onward. Introduced during the Soviet war in Afghanistan, where combat in small villages represented up to 64 % of all accomplished missions, its bunker buster capability and the increased range over RPO Rys showed excellent results: for this reason, flamethrower units were often attached to assault formations. Its use was also remarkable during the conflicts in the northern Caucasus where both Russian forces and Ichkerian forces made great use of them.
Russia, appreciating the effectiveness of the RPO-A in the field, developed a series of new thermobaric launchers munitions in the 1990s to early 2000s. This included:
- The TBG-7: A 105mm rocket, to be fired from the widely issued RPG-7 launcher
- The MRO: A series of smaller launchers, a lighter alternative to the RPO series of launcher, reducing the calibre from 93mm to 72,5mm.
The MRO series consists of the same three variants as the RPO labelled -A (thermobaric), -D (Smoke) and -Z (incendiary). Among these the -A variant was the most widespread in Russian service.
Today, the most widespread thermobaric launchers in Russian service are the RshG-1 and -2, based respectively on the RPG-27 and RPG-26 single use launchers, but replacing the anti tank warhead with a thermobaric one, requiring no additional training for soldiers that are already familiar with the original launchers.
In the mid 2000s Russia modernised some of their thermobaric arsenal, through a modification of the explosive filler, going from an annular construction of the warhead with a RDX central charge and OM-100 around it, to a “homogenous” layout made only from a smaller booster (either RDX or HMX) and the thermobaric filler.
The new filler used here is the LP-30T made from RDX, aluminium, ammonium perchlorate and binder: this composition is in the same vein as western development in thermobaric explosives, such as AFX-757 using ammonium perchlorate to enhance the efficiency of metallic powder burn. Here the aluminium is increasing the energetic potential of the filler.
The US army also realised the need to update their anti entrenchment capability for their infantry, taking into account their experience in Grenada and Panama. In the early 1990s it was decided that the latest AT development by the USMC, the Short Range Assault Weapon (SRAW), if equipped with an alternative warhead, could fill the role of a bunker buster munition, and thus fulfill the US army requirement. It replaced the Top Attack Anti Tank perspective to a warhead made to defeat personnel protected by buildings, bunkers or light armour.
In 1994, the SRAW program became a joint effort from both US army and USMC, each having their own name for their variant of the missile, the “ MultiPurpose Individual Munition “ for the bunker buster and the “Predator” for the Anti-armor.
But this program was rather complex and was expected to have a long development, while the need for a bunker buster munition was urgent, especially considering that, according to Janes, the US army had to borrow 150 SMAW rocket launchers from the USMC to fill their anti-bunker need during the Gulf war.
An interim solution had to be found while the MPIM was being developed which was found in the form of the SMAW-Disposable, later known as the M141 Bunker defeat munition (BDM), a single use launcher firing the HEDP munition of the SMAW already in service in the USMC. The HEDP mentioned here is not of the same kind as the one we are most used to, the dual purpose does not come from a shaped-charge but from 2 different setting for the fuze. The warhead is a rather simple HE, using 1,1kg of aluminised RDX, the aluminum enhancing the blast effect compared to traditional explosives. The fuze will automatically set itself to the most suited fusing time, depending if it hits a hard or soft target.
Both the SMAW HEDP and SMAW-D had decently potent warhead which could breach building walls, destroy light dugouts and light vehicles, but more potent results could be achieved especially with recent development in thermobaric explosives, which led to the development of the SMAW-NE (novel explosive).
The SMAW-NE was a new munition for the SMAW launcher, using a warhead carrying 1,8kg of a new thermobaric filler named PBXIH-135, made from 45% of potent HMX, and a larger amount of aluminium reaching 35%, which greatly enhanced the blast as well as the thermal output of the detonation.
It was introduced in 2004, just in time for its most famous use case, during the Second Battle of Fallujah: there, Marines employed it to great effect against enemy combatants entrenched in buildings. A well-placed SMAW-NE shot, through a window or other opening to detonate inside, would often collapse the entire structure, far more reliably than impacts against an exterior wall. The SMAW-NE was claimed to be capable of penetrating a brick wall before detonating, but anecdotal reports from users judged its penetration performance to be insufficient in most real world combat situations: structures encountered in Iraq were frequently tougher than expected.
As an alternative, many soldiers found that instead of trying to hit a window directly with the NE round, they would first fire a legacy HEDP round at the building to create or enlarge a breach there, “making their own window”, then follow up with the NE round to maximise destructive effect on the target.
The capabilities showcased by the SMAW-NE “gave Marine small units dramatically increased direct firepower“ according to the Marine Corps Gazette, which was later validated by studies by the USMC, during their analysis of the conflicts in Northern Caucasus, where thermobaric launchers were pointed out as invaluable during Military Operation in Urban Terrain.
Inspired by the potential of the SMAW-NE thermobaric warhead, development began on anti-structure munitions (ASM) variants of the M72 Light Anti-Tank Weapon. In 2004, this effort led to the M72 LAW NE, later renamed M72A9. It delivered strong blast performance against structures, at the expense of increased weight and reduced range, while retaining the ability to penetrate a single-layer brick wall before detonating.
To preserve more range and keep weight minimal, a follow-on concept emerged in 2007: the M72 ASM RC (Anti-Structure Munition, Reduced Caliber). It featured a smaller-caliber warhead, loaded with 415g of DPX-6, an explosive slightly stronger than PBXIH-135 used in SMAW-NE, housed in a carbon-fiber casing. This design reduced the danger radius and collateral damage while increasing barrier penetration over previous designs, now capable of breaching a double brick wall before detonation. It featured a selectable fuze delay that the operator could set before firing: either instant (point-detonating) for immediate blast effects, or a delayed mode to allow penetration of a barrier before the warhead exploded inside the target.
Nammo developed several additional ASM variants of the M72 LAW. These include the M72A12 an updated and modernized successor to the M72A9 and the M72A10, which features Fire-From-Enclosure (FFE) capability. However, they are not advertised to match the penetration performance of the earlier M72 ASM RC; official claims limit them to defeating single-layer brick walls.
A particularly valuable feature of the M72A10 and M72A12 is their autonomous, selectable fuze that automatically determines the optimal delay mode: short delay for hard/fortified targets requiring breaching, or long delay for softer targets that the warhead can fully penetrate before detonating. This fuze logic mirrors the proven designs used on the SMAW HEDP round and the M141 BDM.
The anti-structure warheads used in M72 LAW variants primarily rely on kinetic energy combined with the structural toughness of their warhead casing to penetrate barriers. This approach is not the only method for achieving barrier defeat.
A common alternative is to employ a dual stage warhead: a forward shaped-charge precursor first creates a hole through the wall, followed by the main casualty-producing charge in order to reliably detonate the warhead inside the targeted room.
One of the earliest examples of this tandem-warhead approach seeing operational use in NATO was the Bunkerfaust, based upon the Panzerfaust 3 launcher. It was meant to compensate its limitations against heavily fortified positions: the anti tank launcher is able to penetrate fortifications but its post-penetration effects were often deemed insufficient against entrenched personnel.
The Bunkerfaust is a true tandem layout, a forward 106 mm shaped-charge precursor breaches the barrier, up to 36cm of reinforced concrete or brick wall, creating a hole wide enough for the follow through grenade to go through. The main casualty inflicting warhead is the 750g 47mm fragmentation charge, travelling across the barrier, and after 10ms detonating its 100g of explosive and spreading about 2100 fragments all across the room.
The concept of a fragmentation follow through grenade for ASM is not exclusive to the germans, the spanish of Instalaza used this approach all throughout their anti structure line-up for C90, CS90 and Alcotan launchers.
One downside to relying on a fragmentation charge as the primary lethal mechanism is that its effects are typically confined to the single room or space immediately beyond the breached barrier. The light fragments are readily stopped or slowed down by interior walls, limiting their reach. Moreover, the relatively small explosive fill produces minimal overpressure or structural destruction, making it less effective against larger shelters, multi-room complexes, or deeply entrenched positions where blast propagation and internal demolition are desired.
This is why when Diehl worked on the Anti Structure variant of their new RGW-90 Anti structure launcher, they reworked the main charge, moving from the fragmentation grenade to a blast focused charge, containing 700g of blast enhanced filler (assumed to be KS-22A based upon the aspect of the explosive but official confirmation was not obtained). This greatly enhance the effectiveness against traditional building, affecting many rooms instead of a single one and giving greater chance of collapsing the building/shelter. The RGW-90 AS can also be set so that the main charge will detonate within the wall, providing great breaching capability.
Another major advantage of tandem-warhead designs in anti-structure munitions is that the precursor shaped charge, being optimised to create large breaches on barrier, will produce great post penetration effect on AFVs and can even manage to bring the follow through charge within the vehicle interior for the thinly armored AFVs leading to catastrophic damage on target.
The tandem warhead layout proved to be a key driving factor in the U.S. Army’s requirements for the XM919 Individual Assault Munition (IAM) program. This effort aimed to replace both the M141 BDM and various AT4 variants with a single, versatile shoulder-launched system. A core improvement targeted the bunker-busting capability, the XM919 had to reliably defeat a triple brick wall while delivering significant lethality effects.
In 2024, the Army selected Saab’s AT4CS TW offering for the XM919. This design closely resembles the RGW-90 AS in concept: it features a frontal precursor shaped charge for barrier penetration, followed by a main high-explosive follow-through charge optimised for enhanced blast. It includes two selectable fuzing modes “behind wall” and “within wall” exactly like RGW-90 AS.
It should be emphasized that there is no universally superior choice between a basic thermobaric warhead and a tandem follow-through designs each have distinct strengths and weaknesses depending on the scenario. Tandem warheads sacrifice some explosive payload mass, resulting in a somewhat reduced overall blast potential compared to a pure thermobaric round of similar total weight. However, this trade-off provides far greater reliability across a wider variety of targets and engagement conditions: they can consistently defeat thicker or more resistant barriers and deliver lethal effects inside the structure and retain reliable anti AFV capabilities.
In contrast, a pure thermobaric weapon like the RPO-A Shmel or M72A9 excels when the user can place the round accurately through an opening (such as a window or doorway). A direct hit into an enclosed space can rapidly collapse the building or neutralize personnel inside with devastating overpressure and can level relatively huge structures. However, a missed shot ,impacting an exterior wall or failing to enter ,tends to have markedly reduced lethality against sheltered manpower, as the blast wave dissipates quickly outside confined spaces.
An area where basic point detonating thermobaric warheads hold a clear advantage over tandem follow-through designs is in engagements against infantry in the open ,such as troops in streets, forests, open fields, or only lightly entrenched not within a structure but trenches or foxholes.
Tandem layouts are optimized primarily for defeating barriers (buildings, bunkers) or vehicles. When fired at personnel in open terrain, this design becomes suboptimal. The precursor may send the follow-through charge relatively deep into the ground , greatly reducing the effect of an already lighter main charge.
In contrast more basic thermobaric launchers detonates reliably on impact or shortly after, affecting manpower all around it , even a slightly missed shot can still inflict casualties through blast where a tandem would have had nearly no effect whatsoever.
The choice itself boils down to the question of whether you prefer a very powerful blast munition with limited penetration capability but able to be fired at anything or if you prefer a weaker but dedicated anti structure munition with decent anti AFV effectiveness
The Russian invasion of Ukraine has demonstrated that dismounted infantry still desperately needs increased direct firepower across virtually all terrains , from dense forests and peri-urban areas to heavily fortified urban theaters. Entrenchments and fortified positions have posed a persistent problem for assaulting infantry, regardless of the side.
Anti-structure munitions of all types have proven highly valuable in this environment. Ukrainian forces have frequently put captured Russian weapons to effective use in offensive operations, particularly the RPO-A Shmel and RShG-1/2 series. This was especially prominent in the conflict’s early years (2022–2023), when massive captures of Russian stockpiles occurred en masse, and Russia still drew heavily on abundant pre-war inventories.
Intense usage quickly depleted those older stocks. Most recently observed RPO-A and RShG-1/2 in combat bear production markings from the past 1–2 years, indicating Russia has dried up pre-existing stocks and significantly ramped up new manufacturing.
Western-produced anti-structure munitions remain relatively rare in Ukraine, largely due to limited production volumes In Ukrainian hands, this role is primarily filled by domestic and allied Eastern European alternatives. The most prominent are bulgarian series of thermobaric munition, like Bullspike-TB single use launcher or offerings of RPG-7 TB rockets closely followed by domestic ukrainian production of RPV-16, based upon the soviet RPO-A which has seen widespread use since early 2022.
The limited availability of dedicated shoulder-launched anti-structure munitions on both sides of the war has shown that the spirit of Great War-era improvisation is far from dead. Soldiers have reliably resorted to crafting makeshift explosive charges from repurposed ordnance, most commonly anti-tank mines, demolition charges and shells, which are then thrown or placed directly into buildings, basements, dugouts, and trenches to clear or demolish fortified positions.
This practice, much like trench-clearing methods employed over 100 years ago in World War I, dramatically increases the risk to the soldiers involved. They must expose themselves at close range, often standing right at the doorstep of the target, while remaining well within the lethal blast radius and fragmentation danger zone of their own improvised device, relying on a swift exit before the fuze sets off.