Recoilless Weapons in Confined Spaces

Ryan Scheiblein

Recoilless weapons are direct-fire guns distinguished by a system of operation in which propellant gases (or another counter-mass such as a powder or liquid) are expelled from the rear of the barrel in order to offset the recoil generated by forward momentum of the projectile. Many recoilless weapons have smoothbore barrels; however, several well-known models have rifled barrels. Weapons of the latter type are sometimes referred to as ‘recoilless rifles’. Recoilless weapons are generally sorted into two subcategories: crew-served recoilless weapons and shoulder-fired recoilless weapons. Collectively, recoilless weapons are often known as ‘RCLs’ (meaning, simply, ‘recoilless’) regardless of their barrel type or portability characteristics.

RCLs are primarily infantry support weapons; recoilless weapons such as the Carl Gustaf M3/M4 and the AT4 fulfil a similar role to shoulder-fired rocket launchers, serving as an anti-tank supplement for infantry. Heavier systems such as the SPG-9 require a tripod mount for static use and operate as a highly versatile multi-purpose field gun. Increasingly, both types of recoilless weapons fire multi-purpose warheads, and warheads optimised for defeating targets inside structures. Whether shoulder-fired or crew-served, the use of recoilless weapons from enclosed spaces is often necessary due to the advantages of operating within structures over regular field usage. This tactic is not without risk, however, and proper techniques and procedures are critical to ensuring the effectiveness of the recoilless gun team.

Figure 1.1 A U.S. Marine firing an AT4 recoilless weapon during live-fire training in 2008. Note the fired cartridge cases and links being kicked up as a result of the shockwave generated upon firing the weapon (source: USMC).

Urban terrain often provides advantageous firing positions, offering a combination of cover, concealment, height-above-target, and rapid egress—all of which may be beneficial to forces using recoilless weapons to engage enemy armour. Enclosed spaces in the context of urban terrain, are most often buildings with walls and roofs. Despite the drawbacks of firing a weapon which typically operates by violently exhausting propellant gases within an enclosed space, such locations provide highly desirable firing positions. Urban positions allow many opportunities for concealment from visual and thermal systems. Height above the surroundings may provide a clear line-of-sight in a congested urban battlefield and allow the RCL team to look down upon their targets. This also provides specific advantages in the anti-armour role, as the armour of many vehicles is most vulnerable when engaged from the top. At street level or in low storeys, combatants may have good access to egress points.

These advantages must be weighed against the risk of operating within an enclosed space, however. Chief amongst these are the risks generated by ‘backblast’. Backblast is the mass ejected in the opposite direction of the projectile to counteract recoil. In the case of most RCLs, the backblast is takes the form of hot propellant gases which are vented rearward, either through an open tube arrangement, through one or more venturi, or through vents in a cartridge (see Figure 1.1). Some weapons will limit back blast with a ‘two-stage’ launch design, using an expelling charge to launch a rocket-assisted projectile several metres from the gun before a rocket motor engages and continues to propel the projectile. The most well-known recoilless gun of this type is the Soviet RPG-7. Other weapons expel a counter-mass other than gases—such as water, inert powders, shredded plastic, or other materials—in order to mitigate the effects of backblast. In modern weapons, particularly those that have been modified from older designs, the letters ‘CS’ (for ‘confined spaces’) are often appended to a weapon’s designation.

Figure 1.2 Patent Application diagram from a Saab development. Note pointer 20, which shows numerous vents for propellant gases (source: Gustafsson & Irdell, 2009)

Unmitigated backblast can pose serious hazards within enclosed spaces. The pressure waves generated by backblast gases reverberate within enclosed spaces and will often kick up debris and dust which may hinder the timely re-engagement of the target and make the firing position visible to enemy forces (see Figure 1.2). The use of RCLs has also been associated with harm to the firers. According to Price (1978), “Recoilless weapons commonly release a great deal of energy rearward in the immediate vicinity of the crew. If such weapons are fired from within structures, there is concern that in addition to the acoustic hazard to the ear or other organs, there might be hazard associated with flying debris or even structural collapse”. There have been increasing concerns that the long-term use of recoilless weapons may contribute to traumatic brain injury (TBI) or hearing loss, and it is logical to assume these problems could be exacerbated by the use of such weapons in confined spaces.

Figure 1.3 A U.S. military training manual diagram showing the backblast and safety areas for the M72 series of rocket launchers (source: U.S. Army).

In order to mitigate these hazards, U.S. Army field manual FM3-06-11 suggests that the room be well ventilated, with all doors and windows open, and that furniture be left in place. Furniture as well as open windows and doors will limit the reverberation of sound and pressure waves within a room. These waves can also be absorbed by cushioned material such as furniture. While firing weapons without a ‘confined spaces’ modification will still be violently loud and may damage the firer and other occupants’ hearing. However, testing done with cats and goats in the mid-to-late 1970s at the U.S. Army Human Engineering Laboratory at Aberdeen Proving Ground shows that many of the acoustic and overpressure trauma hazards of firing recoilless weapons indoors can be mitigated by using hearing protection (see Price, 1978).

Figure 1.4 Anti-tank Weapons Firing from Confined Spaces. Note the obscuration of vision in the rooms after firing, as well as the sound of falling tiles in the third clip (source: Armament Research Services, 2020).

The U.S. Army requires that all occupants of the room be to the left or right of the firer, against the forward wall of the room. Larger rooms should always be chosen when available as the acoustic trauma risk is reduced with size and good ventilation. When possible the fireteam should wear hearing protection, and ‘remote firing’ with the team detached from the gun is recommended. Minimising the risk of detection is also important. The gun position is often set back from the window or other firing port, with users staying next to the recoilless weapon. Emplaced teams may be assisted by concealed spotters, positioned in the surrounding area, reducing the firing team’s need to expose themselves before engaging the enemy. The importance of a spotter is amplified when the RCL position is in a confined space, as the firing team’s field of view is often limited.

The employment of recoilless weapons from confined spaces is inherently dangerous. However, these risks can be mitigated by weapon design (such as the ‘CS’ types), hearing protection, space selection considerations, and proper firing techniques and procedures. The advantages of cover, concealment, impact angle against armoured targets, and line-of-sight make this tactic crucial within urban environments, and it is likely weapons will be further developed to minimise the backblast effects when used in such a way.


Armament Research Services (ARES). 2020. ‘Anti-tank Weapons Firing From Confined Spaces’. YouTube video. 9 May. <>.

Gustafsson, Par & Henrik Irdell. 2011. Propellant Charge for Recoilless Gun. Patent no. US20090151586A1. Available via: <>.

Jenzen-Jones, N.R. 2015. Recoilless Weapons. Research Note 55. Geneva: Small Arms Survey. <>.

Jenzen-Jones, N.R. & Jonathan Ferguson. 2018. ‘Weapons Identification: Light Weapons and their Ammunition’ in An Introductory Guide to the Identification of Small Arms, Light Weapons, and Associated Ammunition (Jenzen-Jones & Schroeder, eds.). Geneva: Small Arms Survey. <>.

Price, G.R. 1978. Firing from Enclosures with 90mm Recoilless Rifle: Assessment of Acoustic Hazard. Technical Memorandum 11-78. Aberdeen Proving Ground, MD: U.S. Army Human Engineering Laboratory. pp. 1–14.

Remember, all arms and munitions are dangerous. Treat all firearms as if they are loaded, and all munitions as if they are live, until you have personally confirmed otherwise. If you do not have specialist knowledge, never assume that arms or munitions are safe to handle until they have been inspected by a subject matter specialist. You should not approach, handle, move, operate, or modify arms and munitions unless explicitly trained to do so. If you encounter any unexploded ordnance (UXO) or explosive remnants of war (ERW), always remember the ‘ARMS’ acronym:

AVOID the area
RECORD all relevant information
MARK the area from a safe distance to warn others
SEEK assistance from the relevant authorities