A Second Wind for the Lightweight Infantry Mortar

  • Reading time:17 mins read
  • Post category:Infantry

A simple question, was the British Infantry more effective with the 51mm lightweight infantry mortar than it is now, without it?

In an age of swarming drones and artificial intelligence it is very easy to lose sight of the basics, in this case, the ability of an infantry platoon commander to produce smoke, illumination and high explosive effects at range and out of the line of sight to support manoeuvre and closing with the enemy.

The L9A1 51mm mortar was a very simple design, able to be operated by a single person, although usually operated in pairs. The mortar itself weighed 6.3kg and depending on its ammunition nature, was effective at up to 750m. Smoke, HE and illumination rounds were available, each weighing between 0.8kg and 0.9kg.

The rate of fire could be up to 8 per minute.

L9A1 51mm Mortar

The greatest strength of the 51mm mortar was its simplicity and low weight, less than 24kg for the complete weapon and 18 bombs. The training burden was low and it was cheap to use, thus, it was used often in training, and proficiency levels reflect this. Although the HE round was relatively small, aggregating them at the Company level was sometimes used to maximise effects. Because it was organic to the Platoon HQ, it was available immediately and without complication.

You can actually find the 1966 training manual for the 2″ light mortar online (click HERE), the mortar section comes in at a minuscule 35 pages.

Infantry Mortar

Operations in the Middle East depleted ammunition stocks to the point of a decision. The British Army could contract for the remanufacture of out-of-production natures, not in service with anyone else, or, look to the market for alternatives.

The latter was chosen and the Hirtenberger 60mm Platoon/Company mortar was selected.

Hirtenberger 60mm Mortar

The Hirtenberger system was obtained in two variants (although there is some commonality between the two), the M6-410 with baseplate and bipod,

and the handheld version, often termed ‘commando mortar’,

The longer-range (1,300m) and more effective ammunition were seen as a great advantage over the 51mm, especially where platoon engagements might be at longer ranges. The introduction of the L129A1 Sharpshooter was also the result of these longer engagement distances.

The problem with the Hirtenberger system was it was apparently just too heavy and cumbersome, both weapon and ammunition. It provided marginal gains over 51mm but was nearly as heavy as the 81mm. There is no way it was ever going to replace the fiercely effective 81mm mortar and maybe an element of culture also played a part.

Eventually, it was withdrawn.

British Army infantry was left only with 40mm Underslung Grenade Launchers (UGL) for organic indirect fire. A contract was also let to Istec Services for a number of UGL fire control systems. These were called the Rapid Acquisition Aiming Module, developed by Safran Vectronix and Wilcox Industries., show below on an SA80-A2

These still remain in service but it is not known how widely they are used, recent media output from the MoD would indicate not very often. No medium velocity 40mm grenades have been introduced for extending the range beyond 300m, and smoke and illumination natures provide only limited range and burn time.

Framing a discussion on Lightweight Infantry Mortars

Range; There is a constant debate about the ‘typical engagement range’ for dismounted infantry and this often leads to a desire to burden the infantry section and platoon with weapons that cover a significant range, but the infantry cannot afford to carry more weight, they are already significantly overburdened (click here for a long read on just that subject) as it is. The infantry platoon has a good spread out to 2km if equipment like GPMG in the sustained fire role or Javelin is included, GPMG out to 800m, and NLAW and Sharpshooter Rifle out to 500m, with 40mm UGL to 300m.

Effects; The 40mm UGL is a section weapon used in the direct fire mode where the target can generally be seen by the firer. The platoon has no means of providing indirect or high-angle fire with its own resources. Smoke and illumination (visible or IR) are limited to what can be provided by 40mm and disposable rocket flare-type devices with limited burn time and coverage. Discussions on these matters tend to ignore smoke and illumination but they are vital. With the increasing proliferation of thermal imaging equipment, multi-spectrum obscuration will be of increasing importance, perhaps more important than HE.

Employment; Infantry company and platoon organisation changes in response to task and environment, and this inherent flexibility is a great strength. As we move into more disaggregated operations, infantry platoon and company structures might change, and the impact on equipment decisions of projects like UGVs, autonomous carrier type vehicles and even the increasing preponderance of UAVs and loitering munitions has yet to be fully understood. Light Role infantry might also have a very different approach to weight and fire support in the attack to mechanised infantry, again, another set of considerations.

One option might be to push 81mm down to the infantry Company level which would be worthy of discussion, especially on matters of culture, training burden, standards and safety. Another might be to enhance platoon firepower with something like the latest version of the evergreen Carl Gustav. The British Army has certainly been considering such an approach for a number of years. Not only would it improve firepower at the platoon level, but it can also be used to deliver smoke and illumination. This will be the subject of another post but bear that option in mind.

If we make the assumption that ‘something like the 51mm mortar’ is desirable, what would be the qualities needed?

  • A range of natures including smoke and illumination
  • 800m maximum effective range
  • Low training burden delivered by simplicity
  • Low weight
  • Flexibility
  • Sustainability across the platoon

The last bullet point is closely related to the weight, being able to distribute mortar bombs across the platoon.

A Few Options

I have discounted things like armed UAS, loitering munitions and multi-shot grenade launchers as I don’t believe they meet the bullet point requirements, especially weight and simplicity.

There are a number of lightweight 60mm mortar systems available from many of our allies.

Denel in South Africa produce the M4-60,

As simple as they come, the M4-60 weighs 6.9kg. Very similar to the M4-60, Serbia produces the M06C 60mm Commando Mortar with very similar specifications, although slightly heavier at 7.6kg and with a claimed longer range of 1,600m

US Forces use the M224A1, an improved version of the seventies-era M224. It is a 60mm mortar system that can be used with baseplate and bipod or in the handheld configuration.

An excellent description of the 2M224A1 can be found at this link but in the handheld role, it weighs 7.5kg (barrel and M8 baseplate). It is also compatible with the full range of 60mm mortar rounds, each weighing between 1.3kg and 1.8kg. We can also be certain these will be continually developed, an attractive aspect of any US weapon system.

The Rheinmetall RSG60 is relatively new and can be used in two modes, like many conventional 60mm mortars

The usual range of natures is available and it weighs 6.8kg in the ‘commando’ configuration.

The Czech Military Technical Institute VTU designed a 60mm commando mortar system called the LRM Vz99  ANTOS. The same design is marketed and sold under a number of different brand names. It has a liquid-filled sighting window and weighs just under 5.3kg. The maximum range is said to be 1,30om.

An interesting feature of the ANTOS system is the range of natures, including thermobaric explosives, further details here

From Poland, the Tarnów LMP-2017 looks superficially similar to the ANTOS although it is heavier at 7.5kg, and using a steel barrel has a claimed longer life.

All of the above use 60mm mortar ammunition but the French/German Fly-K takes a different approach. Evolved from an old Belgian design it uses a captive piston to reduce the firing signature, 52dB at 100m. More of a rifle grenade projector than a mortar, the individual rounds are actually 51mm in diameter and available in a range of natures with a maximum range of 800m.

The system and rounds are very light, 4.8kg and 0.8kg respectively.

The device in the image below is a multi-shot launcher that can be manually initiated or in response to external sensor input. French forces used them in Afghanistan with a rapidly introduced digital inclinometer to improve firing accuracy.

1.25 into this video

Am not suggesting we rush out and buy it, but the Chinese QLT89 50mm mortar looks interesting, somewhat similar to the Fly-K. It weighs just over 4kg and has a maximum range of 800m.

As with the Fly-K, arguably more of a grenade projector than a mortar, with each individual round weighing approximately 0.7kg.

Another to look at but stand fast with the credit card is the Russian 82mm 2B25 ‘silent mortar’ from Burevestnik

At 13kg, it is at the heavy end but with a maximum range of 1.2km and a very small firing signature, interesting nonetheless.


This is far from anywhere near my usual fare but I do think there exists a gap, and instead of coming up with ever more complex ever more expensive solutions, that gap should be filled with something simple, light, cheap, versatile, and did I mention cheap and simple?

The Fly-K type grenade projectors are certainly interesting, the low signature and low weight make them immediately attractive, as does the hedgehog thing, but do they have the range of natures to make them versatile enough for the longer term, perhaps not.

This brings us back to 60mm mortars, are any of those described above materially different to the Hirtenberger we have recently withdrawn, I certainly don’t know. The ANTOS does look a good option, light and with a good range of natures, but is it durable enough? As always with these things, picking a winner is not something to be done in a blog post, but hopefully, this has demonstrated there are alternatives out there if we chose to fill the gap, and this is before we get into the subject of fire control and target acquisition, yet another subject for a future post.

No doubt we have tried them all, compared rocket flares to 40mm grenades and all manner of mortars to compare manufacturers’ claims to reality, and tested durability and effects, just waiting for the magic money tree to be forthcoming.

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