"Modern British 51mm Mortar Effectiveness" Topic

A current British rifle platoon mounted in Warrior IFVs shows a 51mm mortar in their weapons squad.

Is it really used much in the field or does it tend to stay on the vehicle? If it is used in practice, how is it used? Like a grenade launcher with some extra umph? Doesn't seem quite as capable as the US 60mm company-level mortars, especially with just one per platoon weapons squad.

NOTE: cross-posting to WWII board since a number of WWII armies used 50mm mortars and I thought some who frequent the WWII boards might shed some light on the subect (either through historical or personal knowledge).

I asked this question of a member of the RAF Regiment a couple of months ago.

His reply was that its small and portable and can deliver HE or illumination rounds where and when required – a very useful weapon in his opinion.

It is essentially a lightened version of the WW2-era 2-inch Mortar and is used in the same manner as a platoon-level indirect fire support weapon. Elevation is judged by dialling in the range and then watching the integral spirit-level bubble, while azimuth is judged simply by looking along a white line painted up the barrel – it's very quick and easy to use.

Unlike most mortars it has a trigger, which is activated by tugging a lanyard. This means that you can lie up in an ambush postion with a round loaded and then pull the trigger at the moment of ambush.

There is an excellent description of its use in action in Doug Beattie's superb 'An Ordinary Soldier'. Judging from Beattie's account, it seems to be a very effective weapon in the right hands.

Among its other eccentricities, one of the oddities the British Army has maintained for a bit over half a century is a fondness for the light mortar as a platoon weapon. Most armies at the start of WW2 included weapons of this calibre on their normal infantry orbat. The Germans and Russians gave up on them by mid-war; the Japanese, who were more enthusiastic than even the Brits in having three "knee mortars" per platoon, kept them until the end. One of the things that seems to have influenced the decison to keep or discard them is the simplicity and bulk of the weapon's design. The German 5cm was a hefty beast with cross-levelling twiddlers and all sorts of controls on it, and the Russian 50mm had a proper bipod and sight, whereas the Japanese "knee mortar" and the marks of the British 2-inch that were kept were both very simple (and therefore light) weapons, consisting of little more than a tube and a vestigial baseplate. I have carried a 2-in mortar on exercise -- although, sadly, they only gave it to me to carry once the ammunition had all gone -- and it really is very easy to sling over your shoulder and tote around.

For HE fire, according to a WW2 OR reports I have seen, you can reckon in rough terms that a WW2 2-in mortar bomb has about half the lethal area of a 60mm bomb, which in turn packs about half as much doosh as an 81mm bomb. However, the instant availablility of 2-in HE could not be matched by having to ask for fire through an MFC, and some sources considered the 2-in the main firepower resource of the platoon. The other extremely useful task for the 2-in is smoke, and I suspect that the British fondness for attacking "two up and bags of smoke" is at least partially accounted for by the ready availability of obscurants to British platoon commanders. Finally, of course, it can put illuminants to a useful distance.

The British Army is now going to retire the 51mm mortar, not because it is not useful -- it has proven in the latest fighting that it is -- but because some idiot in defence procurement let the manufacturer close down the line on which its ammunition was manufactured. This means that the Army is now adopting the 60mm mortar, which, while it may be an admirable weapon for all sorts of reasons, is a good deal heavier, and fires ammunition that is twice as heavy.

All the best,

John.

The 2-inch mortar was originally much heavier, with a base plate and sighting/elevation mechanisms. I think the modern one is based on the lightened WW2 airborne version.

The Jap 'Knee Mortar' was somewhat different, being properly termed a grenade-discharger. The rounds were much lighter than 2-inch mortar rounds – both in terms of HE filled and in fragmentation – the casings were often plastic. Organisationally they were used in one of a platoon's squads in lieu of an LMG. It made a lot of noise and in the right situations was a handy weapon, but packed nowhere near the punch of a 2-inch mortar. I'd say that they were more akin to an M79 or M203 or UGL than a mortar.

I didn't know about their departure from service. If we're stuck with 60mm, why don't the British Army go with the South African 60mm 'Patmor' (Patrol Mortar)? The Patmor has all the features of the 51mm, but uses the larger 60mm bomb. This came about because the SADF got tired of lugging 60m mortars around the Bush and wanted a 2-inch style weapon – I imagine that the British Army will be forced to learn this lesson all over again… They're even made by British Aerospace now that BAe owns most of SA's arms industry!

I remember reading somewhere that, as the 2" has a trigger, it can be fired horizontally and was used for breaching buildings in urban combat.

The British Army is now going to retire the 51mm mortar, not because it is not useful -- it has proven in the latest fighting that it is -- but because some idiot in defence procurement let the manufacturer close down the line on which its ammunition was manufactured.

Well, since my new project is set in 2020 maybe I can delete from my ORBAT? :-)

Whether or not I include it I'm interested in how it's actually used today. Based on the comments above it seems like it really is a "super grenade launcher" rather than a traditional indirect fire weapon dropping rounds on unseen enemy hiding behind terrain.

I just can't imagine that its small burst radius and limited ammo supply would allow it to plaster an area large enough and long enough to be effective in an indirect fire role.

Maybe it makes sense to phase it out and replace it with one of the new rocket launchers using the latest anti-personnel warheads? In urban combat they seem to have proven very useful and can carry heavier warheads.

Anyone know how the 51's warhead compares to a 40mm grenade launcher? If not significantly better maybe it "falls between the stools" of the 40mm GL and warheads used on LAWS and AT4s when providing direct HE support at platoon level.

"Whether or not I include it I'm interested in how it's actually used today. Based on the comments above it seems like it really is a "super grenade launcher" rather than a traditional indirect fire weapon dropping rounds on unseen enemy hiding behind terrain."

It is actually used today in exactly the same way as it was used in WW2, as the platoons 'mini artillery'. The fall of shot is often observed by the gunner however. The March 1944 'Infantry Fieldcraft and Training' manual explains and demonstrates the role and usage of the 2" mortar, and it seems to be used in an identical manner now.

In the first series of 'Ross Kemp in Afghanistan' there is camera footage of one being used by the Royal Anglians in a firefight with the Taliban.

The 2-inch mortar isn't always used in a line-of-sight manner. In Doug Beattie's account mentioned above, he was calling in rounds as a forward observer, onto targets invisible to the mortar party. As has been stated – the 2-inch/51mm mortar is a kosher mortar and not a grenade-launcher like the Japanese 50mm.

Remember that modern British infantry already have the 40mm UGL (Underbarrel Grenade Launcher) and various rocket launchers for line-of-sight work – the 51mm mortar has a much larger round than a 40mm and greater reach and flexibity than a rocket-launcher, though less punch.

R Mark Davies wrote:

The 2-inch mortar was originally much heavier, with a base plate and sighting/elevation mechanisms. I think the modern one is based on the lightened WW2 airborne version.

There were dozens of marks and sub-marks of 2-in mortar in British service; my point was that the ones that were retained were the ones that did away with the fripperies like monopods, sights, and large baseplates.

The Jap 'Knee Mortar' was somewhat different, being properly termed a grenade-discharger.

Indeed, but then what the difference is between a "mortar" and a "grenade discharger" is a bit of a tricky question when in many languages what we call a mortar is called a grenade discharger (lance-grenades, granatwerfer, bombekaster, take your pick). Technically I believe the Japanese designation was different from that use for other "infantry high-angle guns", but as it is an infantry weapon firing in the upper register with the recoil absorbed by the ground, it is very clearly functionally a mortar.

The rounds were much lighter than 2-inch mortar rounds – both in terms of HE filled and in fragmentation – the casings were often plastic. Organisationally they were used in one of a platoon's squads in lieu of an LMG. It made a lot of noise and in the right situations was a handy weapon, but packed nowhere near the punch of a 2-inch mortar. I'd say that they were more akin to an M79 or M203 or UGL than a mortar.

The Model 89 HE shell weighed in at 28 oz, 2-in mortar HE at 35 or 36 oz depending on the type of fins, and although 40mm grenades vary by model the HE ones seem to be around 8 oz. Given also that 40mm and 30mm GLs are not typically used in the upper register, and have their recoil absorbed by the firers shoulder, I find it very hard to see how you can believe that they are more like the "knee mortar" than is the 2-in.

The following is from Colonel John George's splendid book, "Shots Fired in Anger" (National Rifle Association of America, 1981):

"We called this particular weapon the "knee mortar" on Guadalcanal although we all knew that it could not be fired from the knee or thigh. It was a ground launcher and would project ordinary grenades beautifully for short distances -- not far enough and not with sufficient destructive effect to be technically considered a true mortar, however.

"But when they loaded this same gun with shell-type projectiles, longer and more streamlined than the grenades and containing a heavier explosive charge, it would step right out of its class and become a near-equal -- in the jungle -- to our own little 60mm mortar. For handiness and utility in small unit or patrol operations it was even better than the 60mm.

"It was easily carried; its ammunition was light and handy; and it could be put into action ona very few seconds notice. It was eminently suited for use against Americans -- for, as I have previously mentioned -- we had nothing with which to talk back."

[…]

"The official designation of the knee-mortar was the M-1929 50mm grenade launcher. (The obsolete M-1921 is not considered here since it was unrifled -- purely a grenade-launcher -- and only a few were found.) The M-1929, fired our way, had a set pattern of behaviour and we were damned sorry to have it used on us so often. It could always go into action faster than our 60mm. Always we would feel the shells coming down on us in the very beginning of any kind of a fight, the explosions following immediately after the first few rifle shots, and our ability to reply was only theoretical. We had to go to a lot more trouble to make our 60mm gun do the job of answering these quick shooting knee-mortars. We had taken the bipods off and carried only a few light shells, burdening down the advance guard with the load, and yet the best we could do would be to commence firing a full minute after the first enemy shells had come down. This was because the tube and shells were too heavy and bulky, the latter usually packed or slung in a manner that would cause a period of fumbling before they could be armed and dropped in the tube. […] Lightweight is the greatest single advantage an Infantry weapon can have."

[…]

"The M-1929 was a very lighweight job, but it threw a man-sized shell, not far behind our own light 60mm in effectiveness."

Agent Brown wrote:

I remember reading somewhere that, as the 2" has a trigger, it can be fired horizontally and was used for breaching buildings in urban combat.

You aren't going to "breach" much with a 2-in or 51mm round, at least, not unless you are firing in the anti-shed role. The trick is to post the bomb through a window.

All the best,

John.

"I remember reading somewhere that, as the 2" has a trigger, it can be fired horizontally and was used for breaching buildings in urban combat."

And also against tanks (when the ammo for the PIAT ran out) in Operation Market Garden.

If I am not mistaken, the 51mm mortar has around twice the range of the UGL, which can be an advantage sometimes.

It probably also has a lower signature than a rocket launcher or recoilless rifle (and a lack of back-blast) which can be an advantage. Of course being able to hide the weapon completely behind cover and use observed fire helps even further.

And the high trajectory can be handy when you want to drop them bombs into foxholes or trenches.

This is all very interesting!

Anyone have detailed stats on the 51? Effective range? Armor pen.? Ammo load? etc.?

Any idea how various wargame rules have treated them compared to other weapons such as GLs, 60mm mortars, and ATRLs?

Anyone have detailed stats on the 51? Effective range? Armor pen.? Ammo load? etc.?

- Range: I have seen it referred as 750-800 meters.
- Armour penetration: probably rather insignificant.
- Ammo load: not sure about modern, but in WWII the gunner carried mortar and 6 rounds, while other mortar team members carried 12 rounds each.

Don't forget the illumination rounds – potentially very useful in real life, but something not really addressed by most rules out there.

– Ammo load: not sure about modern, but in WWII the gunner carried mortar and 6 rounds, while other mortar team members carried 12 rounds each.

That would seem to be a challenge in modern usage unless multiple members of the platoon at large carry ammo. In the modern British TO&E there's just a lone 51 gunner and (maybe) his squad leader to carry ammo. No true mortar "team".

I have the British Army manual from the early 50's and it makes it pretty clear its role is envisaged as the provision of smoke by day and illumination by night, although it makes reference to some theatres holding stocks of HE ammo.

Hi John, true enough – it is largely a matter of semantics in terms of description. But I would argue that the British 2-inch mortar in WW2 was employed in a subtly different role to the Japanese 50mm – the Japanese 50mm was very much a line-of-sight, close-in weapons system, whereas the 2-inch had a degree of flexibility afforded by range, accuracy and truly indirect capability.

The Japanese 50mm came about due to the WW1 experience of organising one section of a four-section platoon into 'rifle-bombers'. The tactical employment and performance was essentially little different. It also lacked any sort of sighting mechanism and had nowhere near the range of the 2-inch mortar. As already discussed, its effect often left a lot to be desired and in British accounts was often derided as merely a 'lot of noise'.

Remember that British rifle grenades of the period also required the operator to brace the rifle against the ground, due to the additional charge. This does not really indicate a different role to the M203 or UGL of latter years.

Coming back to the subject – regarding ammunition: in many archived unit orders it mentions that each man in the platoon should carry forward x many rounds o 2-inch mortar ammunition to a pre-arranged dump in the FUP, where the 2-inch mortar will then set up and use the dumped ammunition.

As with any heavy weapons system, the 2-inch/51mm mortar will suffer from ammo shortages when in a mobile, foot situation, but will have considerablt more ammunition available if supporting a deliberate attack or if defending from a fixed position or if utuilising a vehicle or mule for ammo resupply.

You aren't going to "breach" much with a 2-in or 51mm round, at least, not unless you are firing in the anti-shed role

"Anti-Shed Weapons of WWII" is a sadly missed Osprey. Given that much of Britain's creative Ooomph dwells in said sheds, such a weapon in the hand of an invading Kraut would have been a savage kick to the goolies of the British Lion.

I too had heard that Col. Frost went about with a 2-inch mortar potting shots at tanks. Unless these were 'Otterbury Incident' tanks, what on earth was he trying to achieve?

Pat

R Mark Davies wrote:

But I would argue that the British 2-inch mortar in WW2 was employed in a subtly different role to the Japanese 50mm – the Japanese 50mm was very much a line-of-sight, close-in weapons system, whereas the 2-inch had a degree of flexibility afforded by range, accuracy and truly indirect capability.

The 2-inch mortar I carried (I think it must have been a Mk 8*) had a white line painted down the barrel for sighting, so whatever "truly indirect capability" it may have had cannot have been greater than that possessed by the "knee mortar".

As for range, it is surely very well known, according to any source you may care to consult, that the Type 89 outranges any model of 2-in mortar by at least 200 yards.

As to accuracy -- I have no figures on that, but as the Type 89 is rifled and uses a copper driving band, and the 2-in has no means of obturation other than the fit of the body in the smooth bore, I doubt very strongly that the 2-in was the more accurate. Have you any evidence that it was?

The "subtly different" role of the 2-in and Type 89 seems to be so subtle that many published experts have entirely failed to spot it. John Weeks' first 1975 edition of "Jane's Infantry Weapons" puts the Type 89 in the section on mortars, not grenades and grenade launchers, as do Chamberlain and Gander in their WW2 fact file on mortars and rockets. Jac Weller, in his "Weapons and Tactics: Hastings to Berlin" says:

"This British 2-in mortar deserves special praise; it is a simple little weapon but has outlived all its WW II companions. It resembles the Japanese knee-mortar, […] there are no adjustable sights."

As already discussed, its effect often left a lot to be desired and in British accounts was often derided as merely a 'lot of noise'.

I'd be interested to know what accounts you are referring to. They seem to contrast rather strongly with Col. George's first-hand account.

Sane Max asked:

I too had heard that Col. Frost went about with a 2-inch mortar potting shots at tanks. Unless these were 'Otterbury Incident' tanks, what on earth was he trying to achieve?

I'm not saying this is what he had in mind, but, if it were me, I'd be hoping to do some good with a WP round. Even if it's only to annoy the crew by setting fire to their external stowage or camouflage.

All the best,

John.

Hi John,

I've got these figures for comparitive range:

Type 89 Effective range – 120-200 yards
Type 89 Maximun Range – 670 yards

2-inch Effective Range – 500 yards
2-inch Maximum Range – 850 Yards

The Type 89 had two very different types of ammunition – the Type 89 50mm shell is the one you describe, but it had a low explosive yield and was usually made out of plastic. The Type 91 50mm shell was a heavier 'pineapple' type fragementation grenade that had a greater explosive yield but did not have the driving band and only went 200 yards max.

The Mk8 2-inch mortar was the lightened airborne version. The other versions had sights and a spirit level for ranging. However, I agree that in reality, troops often adopted a 'that's about right' approach to these things. The modern 51mm combines the white line and the spirit level.

The Japanese Type 98 had no mechanism for sighting or ranging whatsoever.

As discussed above, it was doctrinally used as a grenade launcher, 2 or 3 within a rifle section in lieu of an LMG, and not as a platoon-level fire support element controlled by the platoon commander like virtually all other light mortars.

As for the Allied assessment of its performance; it is derided in a number of personal and unit histories. However, most also comment that the loud bang caused by the weapon was unpleasant and annoying. Lyall-Grant, Hamilton and a couple of others make comment on it.

R Mark Davies wrote:

I've got these figures for comparitive range:

Type 89 Effective range – 120-200 yards
Type 89 Maximun Range – 670 yards

2-inch Effective Range – 500 yards
2-inch Maximum Range – 850 Yards

The first appear to come from Wikipedia, whose only referenced source is Col. George's book which I gave extracts from. Whoever wrote the Wikipedia entry seems to have got themselves muddled about the maximum range firing grenades and the maximum range firing the purpose-built shell. This has already been explained in the extracts I have posted from George's book, so…

The Type 89 had two very different types of ammunition –

… I'm fully aware of that, thank you.

I am a trifle bemused as to what anyone thinks is the difference between "maximum" and "effective" range with a mortar, as the round still goes bang at maximum range. But as for the idea that any mark of 2-in mortar can reach 850 yards, well, the only way I can think of doing that is by using a 325-yard firing lanyard. The maximum range of 525 yards is given in the 1975 Jane's Infantry Weapons, and in WO 291/157, "Performance of 2-in mortar" (which I will mention again later). The maximum range in the aide-meoires issued when I was in the TA was 500m, which is pretty much the same. As the 2-in round is propelled by a cartridge between the fins, there seems to be no possibility of adding increments to boost the range above the "official" maximum in the way one could with, say, the 3-in mortar. So, I have to ask what your source is for that figure; it sounds to me as if someone has got muddled up with the 51mm (which goes much further than the 2-in, thanks to the Makrolon obturating ring).

the Type 89 50mm shell is the one you describe, but it had a low explosive yield and was usually made out of plastic. The Type 91 50mm shell was a heavier 'pineapple' type fragementation grenade that had a greater explosive yield but did not have the driving band and only went 200 yards max.

Nope, you've got these the wrong way round. The Type 91 weighs 18.8 oz, and goes to about 200 yd; the Type 89 weights 28 oz, and goes to over 700 yd. See, for example, Tantum & Hoffschmidt's "Second World War Combat Weapons: Vol. 2, Japanese".

The Mk8 2-inch mortar was the lightened airborne version.

Yes. And the version I carried was the Mk 8*, '*' pronounced 'star', which was an infantry version (see Jane's '75 for a complete list of marks).

The other versions had sights and a spirit level for ranging.

The one I carried did not. Weeks says that "Those marks of Mortar designed to be used with the Universal Carrier had a baseplate instead of a spade" and "The Marks used in the carrier had had elevating and traversing clamps and used a sight (Sight no 4 Mark 1). This had a range scale graduated in the upper and lower registers from zero to 525 yards. The infantry and airborne mortars were attached directly to their base spades and had no sights."

As discussed above, it was doctrinally used as a grenade launcher, 2 or 3 within a rifle section in lieu of an LMG, and not as a platoon-level fire support element controlled by the platoon commander like virtually all other light mortars.

Take a look at

tinyurl.com/39f6kkp

and scroll down to figures 2 and 3 and you will see, lovingly represented in diagrammatic form, Japanese platoon attack tactics where the grenade launcher section is used precisely to cover the platoon into the attack.

As for the Allied assessment of its performance; it is derided in a number of personal and unit histories. However, most also comment that the loud bang caused by the weapon was unpleasant and annoying. Lyall-Grant, Hamilton and a couple of others make comment on it.

I'm guessing that you read much the same books as I do, and so these refer to "Burma: The Turning Point" and "War Bush" respectively. If so, could you provide page numbers? I have just skim-read the first of those books, and can find no reference to knee mortars other than in an appendix (which makes no coimment on their effectiveness, but credits them with a range of 700 yards).

Now, back to WO 291/157, "Performance of 2-in mortar". Obviously the modern 51mm ought to do better than this, but I can't give you effectiveness figures for that. The following table shows, based on trials conducted in 1942, the hit probability per round, and the number of rounds needed to secure a 50% chance of a hit, against a man-sized target in the open, for both low-angle and high-angle fire. Use of the sight, incidentally, is recommended; and another snippet is that the chance of hitting a target under 2-in mortar illumination at night is about a third of that in daytime.

Range (yds)	200 LA	400 LA	525	400 HA	200 HA
Hit probability	10%	3.8%	6.8%	4.9%	6.0%
No. bombs	7	18	10	14	12

All the best,

John.

You win ;o)

You've got all the references to hand and I'm working purely from hazy memory away from home.

Take care,

Mark

The 2-inch mortar isn't always used in a line-of-sight manner.

Interestingly, neither was the PIAT.