US Mortar 60mm, M2

There have been several discussions over the years where use of the mortar and a few of it's firing procedures were discussed. These were always cursory and were just intended to give the other discussion participants an idea of how the mortar was fired and adjusted. I was reading up on something else this morning and came across this web page. When I went to infantry school I was trained as an 0331 Machine Gunner and had just received familiarization training in the employment of the 60mm mortar (yes we still had the M2, we got the M224 starting in 1978), when I checked into my unit we were well over TOE in 0331's so I spent 6 months as an OJT mortarman 0341, before I moved back to my primary MOS. This little page is great, procedure is spot on and it even has the tone of the instruction nailed. The mortar sight 60/81mm M4 was still manufactured well into the 1980's which let's you know how long the M2 stayed in service with Reserve/National Guard units (the M224 uses the mortar sight M64/M64A1). The same basic HE M49A3-A4 with PD fuze M525, WP M302-302A1 and Illum M83-A1-A3, ammo was still used with the follow on M224 system until supplanted by newer rounds starting in the mid-80's. The only thing it doesn't really cover is the use of "increments", tiny, detachable propellant charges that come with the rounds and are used to increase range.

Read and enjoy:

M2 60mm Mortar employment:
60MM Mortar Demonstration

60mm Mortar Ammunition:
60mm Mortar Ammunition And Fuzes

 

What is the real accuracy of mortars (assuming the zero is correct) at various ranges? Say, the target is 500, 1000, 2000 meters away, how close would you expect the round to land?

 

Being a mortarman is both art and science, some of the really good ones can drop 4 out of 5 rounds in a 55 gallon oil drum at @2000 yards (the WWII era M49A2-A3 had a max range just shy of 2000 yards and the last iteration of the round the A4 just a hair over 2000 yards). Generally a well trained crew would have an accuracy rating between very good and excellent. Even an average crew can keep all rounds within about half the burst radius of the initial on target round.

 

Remembering my training on mortars in the late 60s-early 70s, I would have to say that their accuracy was not all that great. A bunch of us were trying to hit a target about the size of an average living room. I remember us trying to bracket in on it and not being able to hit it and that was at a range of perhaps 700 to 1000 mts. One of our instructors told us that if you got with 20 meters of the target that was about the best you could expect at that range. Those stories of putting rounds down chimneys and such should be looked at with skepticism. Of course anyone can get lucky.

 

Is there a granularity to the range adjustments? I can see just "nudging" the base plate a bit to get some pretty fine angular control. Of course I guess you could do the same by stacking something (paper) under the legs or base plate. That would take care of fine tuning the pointing of the mortar but there's still the variation due to propellant, projectile, and variable environmental factors. Can't claim any personal experience with them though.

 

The M2 was an evolution of the Brandt mortar and was known for it's accuracy and longer range than other 50-60mm mortar classes. It like all weapons systems is an amalgamation of all it's components the mortar, the sight and the ammunition. The M2 was one of those systems where everything came together. I would guess, and you can correct me if I'm wrong, but you probably trained on either/both the British 2" or L9A1 51mm systems. If so it's similar to the US M19 which began development in 1942 as a replacement for the M2 but it's lack of accuracy led to it being scrapped. The bipod and relatively large baseplate made the M2 a more stable firing platform.

M2 60mm mortar



British 2" mortar



British L9A1 mortar



It's all about the stability of the platform and how fine of adjustments you can make.

 

Yes there are a lot of things that can effect accuracy and ammunition is one of them. In very cold weather around 0 Fahrenheit and below there is often the issue of incomplete burning of propellant. If you're firing the same lot of ammunition and you haven't removed the rounds from their fiberboard containers prior to needing them you get a relatively consistent performance. If you're carrying them exposed to the elements rain and high humidity (absorbed by the increments) you get greater variation between rounds. Muddy ground and loose sand effects variance between rounds because you lose some measure of stability, in those cases you often can place sandbags on the legs and under the base plate or dig it in enough to get a firm base.

 

there are around 14 variables that affect the trajectory of a round. Variations in wind direction and speed can have a big effect and are outside the control of the mortar-man. If its a steady wind in a constant direction it is possible to apply a correction, but if the wind speed increases or drops or backs or veers the round can fall some way + or - left or right.

There is also the question of the 50% zone.

 

Of course there are many, many factors in any type of ballistic calculation in every weapon from a rifle bullet up to the largest artillery piece. Wind, unless it is gusting in excess of 10 kts is not a big factor in the 60mm, it is more of a factor for 81's and an important factor in four deuces and larger. Those mortars are considered long range mortars while the 60 is short range. The long range mortars rate FDC's and receive ballistic met messages. The 60 is less effected by winds due to a relatively short flight time, relatively heavy HE round with a good BC (ballistic coefficient). Even with a lateral wind gusting up to 10 knts all rounds should land in an imaginary circle, centered on the registration round, with a diameter of 1/2 the burst radius of the round. More important to the accuracy of the 60, as I stated earlier are temperature, if the round has been removed from it's crate/ammo box and individual container. Ammunition lot, moisture and barrel condition are also important factors.

From FM 23-91 Fundamentals of Mortar Gunnery

b. Ammunition Lots. Each lot of ammunition has its own performance level when related to the same mortar barrel. Although the round-to-round probable error (PE) within each lot is about the same, the mean velocity developed by one lot may be higher or lower than that of another lot. Variations in the projectile, such as, the diameter and hardness of the rotating disk, affect muzzle velocity. Projectile variations have a much more apparent effect on exterior ballistics than on interior ballistics.....

f. Temperature of the Propellent. Any combustible material burns rapidly when it is heated before ignition. When a propellent burns more rapidly, the resultant pressure on the projectile is greater, increasing muzzle velocity. Firing tables show the magnitude of that change. Appropriate corrections to firing data can be computed, but such corrections are valid only if they reflect the true propellent temperature. The temperature of propellents in sealed packing cases remains fairly uniform, though not always standard (70 degrees F).

(1) Once the propellent is unpacked, its temperature tends to approach the prevailing air temperature. The time and type of exposure to weather result in propellent temperature variations between mortars. It is not practical to measure propellent temperature and to apply corrections for each round fired by each mortar. Propellent temperatures must be kept uniform; if they are not, firing is erratic. A sudden change in propellent temperature can invalidate even the most recent corrections.

(2) To let propellents reach air temperature uniformly, ready ammunition should be kept off the ground. Ammunition should be protected from dirt, moisture, and direct sunrays. An airspace should be between the ammunition and protective covering.

(3) Enough rounds should be unpacked so that they are not mixed with newly unpacked ammunition. They should be fired in the order in which they are unpacked; hence, opened rounds are fired first.....

g. Moisture Content of Propellent. Handling and storage can cause changes in the moisture content of the propellent, which affects the velocity. This moisture content cannot be measured or corrected; also, ammunition must be protected from moisture.

 

All the above is fine but it sounds like you're trying to turn the wonderful, down and dirty little mortar into a regular artillery piece. A couple of things to remember is that since mortars are high angle/fin stabilized weapons, they will never be really accurate as tube artillery (which in turn is being replaced by rockets guided by very accurate GPS). The mortar's forte is getting quick fire on targets and rapidity of fire, especially on targets that can't be hit with direct fire weapons. Because they're placed lower down in the food chain, (usually Bn but in this case company level), a platoon or company commander can get a much quicker response than with artillery (divisional level or higher). In WW2 almost every combatant started out with a small mortar. The Germans had their 50mm and the British the 2" as seen above. Only the M2 survived beyond 1942. To replace the 50mm the Germans took their 80mm mortar and shortened the barrel and gave it a smaller baseplate (stummelwerfer?). They traded range for portability while keeping the same lethality. Every time someone mentions the 60mm mortar I always see that Mauldin cartoon, "K Company artillery speaking". By the way, the M2 was still being used in Vietnam while I was in the service!

 

No, not trying to conflate the capabilities of the mortar at all, but not underestimating them either. The 60's are carried at the company level, the 81 at the battalion level. Tube artillery isn't going anywhere, neither is the mortar, in US forces the HIMAR was simply the replacement for the really big guns, 8", 175mm, and such. The 155mm howitzer is alive and well. The M2 actually stayed in service into the 1980's with some units (it's actually the mortar I first trained on), it started being replaced by the M242 in 1978. The reason it stayed so long is because it outranged most of it's contemporaries, while retaining a high rate of fire, good accuracy and had a very effective HE round. Mods of the M49 HE round served on for some time in the M224 system. As stated in an earlier post the US M19 that was developed as it's replacement (starting in 1942) lighter weight, with a minimal base plate and no bipod, never managed to supplant it because of lack of accuracy. They added the M2's bipod to the M19 at one point, but it never achieved the level of accuracy necessary to replace the M2.

Here's some info showing that mortars are here to stay, not just the M224 60mm at the company level and the M252 81mm at the battalion level, but larger mortars as well:

The US Army fields the 120mm Soltam Cardom in the M1129 Stryker, and the M120 120mm mortar (since 1991).

The Marine Corps is now fielding the M327 120mm mortar system:


A new precision guided 120mm mortar round is being developed:
Marines Fire Precision-Guided 120mm Mortar

Also the British Army at one point intended to replace it's 51mm mortar with an underslung 40mm grenade launcher similar to the US M203. However, the plan left a capability gap and in 2007 they issued an Urgent Operational Requirement (UOR) and acquired the M6-895 60 mm Mortar which provides the infantry with a light mortar capability out to almost 4 kms in both the direct and indirect fire roles. They do still field the L6A1 81mm at the battalion level.

From thinkdefence.co.uk

"At the platoon level, we used to issue the L9A1 51mm hand held mortar, a weapon of a type often referred to as “Commando” mortars. As you all probably know, apparently our involvement in the Global War on Terror used up our stocks of 51mm ammo rather faster than had ever been planned, and then we found out there was no economical way to acquire more. This, alongside a long held desire by some within the infantry establishment who were envious of the US M203 under barrel grenade launcher, to see such weapons deployed widely, eventually saw the official replacement of the 51mm platoon mortar with up to two 40mm UBGL per section. Of course the 51mm had greater reach than the 40mm, it made a bigger bang, its illumination rounds produced more light, and its smoke rounds burned for longer, making more smoke, etc etc I have no issue with this, different tools for different jobs. New model 40mm grenades (medium velocity) have increased range, and increased bang, but they are still really direct fire weapons, not suited to ballistic-ally lobbed, in-direct fire.


However as it ever does, the cyclical nature of wars and technology made sure that what went around came around, and the UK issued a UOR for lightweight 60mm mortars. My understanding of this, and I could be wrong here, is that we first went out for such kit for limited special forces use, and then broadened the procurement to what in effect was a direct replacement for the 51mm as a platoon level weapon for use by non-SF troops in Afghanistan."

 

Good heavens Price, I certainly wasn't downing the mortar, in fact just the opposite! To me, the mortar is a wonderful tool and fills a much needed niche in the tactical matrix. To me, the mortar is simple, easily concealable, very portable and...very deadly. These are good things! My point was that getting overly sophisticated with such a weapon somewhat obviates its advantages. Remember "KISS"? In Normandy the majority of American casualties were caused by mortar fire. With the advent of radar/computer systems able to pinpoint mortar and artillery positions by the trajectory of the rounds, portability is a very, very good thing! By the way, that 120mm mortar of the Marines looks very much like it was inspired by the Soviet/German 120mm mortar!

 

I read somewhere that the 81mm mortar actually has a similar explosive charge to a standard 105mm gun. I'm not sure that large charge equates to the same bang with that thin case, but still, that's a formidable weapon to have down at the grunt level.

I've read some interesting accounts of the rifled 4.2 inch (107mm) 'chemical' mortar battalions in the ETO. The chemical shells were never deployed, but with explosive shells they had a range of over 4000 yards and gave you an outsized bang for your buck. These battalions were independent and attached to assault divisions from the Corps or Army level, and often mixed big White Phosphorous with the HE shells to burn up German positions prior to an attack. The initial rate of fire was something like 20 rounds per minute from each tube (until they heated up), so a whole battalion of these dumping on a German position without warning must have been hell for those on the receiving end.

 

Looking at:
81mm Mortar Ammunition And Fuzes
81mm mortars listed there have 2.1lbs of explosive.
http://64.78.11.86/uxofiles/mulvaney/techdatasheets/81mm-HE-M821.pdf
this one has 1.6lbs.
According to wiki at:
M2 4.2 inch mortar - Wikipedia
4.2" mortar has 3.64 lbs of explosive.
Accodring to:
http://64.78.11.86/uxofiles/mulvaney/techdatasheets/105mm-HE-M1.pdf
105mm HE has either 4.8 or 4.25 lbs of explosive.

That said the thicker case would likely produce more fragments and more dangerous ones. Blast effects for a given weight shouldn't be affected much by the case. The higher velocity of the arty round will tend to man that the fragments are distributed in a more conical shape along the direction of travel. Higher angle will also tend to make cover less effective for targets engaged by mortars unless overhead protection is available.

 

@ KB and lwd: First of all, having seen both 105mm how and 81mm mortar rounds impact, I would have say that what lwd's figures show is absolutely correct. The 105 definitely has more "bang". However, given relatively dry ground, a mortar gives a better, more circular fragmentation pattern than an artillery round. Arty rounds hit the ground and in that infintessimal micro-second between the round hitting the ground and it going off, generally slide a little bit longitudinally along the ground. This means that about half the fragments go into the ground or up in the air, while about half more or less are propelled sideways, parallel with the ground and are the dangerous ones. The safest place (least dangerous?) place within the lethal area of the impact is to the rear. This is of course, unless the round is fired at a high angle and then round comes straight down like a mortar bomb and spreads the fragments in a circle. Both are lethal for people not behind cover. Overhead cover is good only against air bursts unless it's very stoutly made.

The 4.2" mortar's big difference compared to the 81mm is that the 4.2's round is rifle stabilized while the 81 is fin stabilized. This is achieved by the 4.2" round having a base similar in function to the old Minnie ball of civil war fame. The mortar shell is dropped down the barrel. When the propelling charge goes off the propelling gasses force a flange around the edge of the base outward and thus engage the rifling in the barrel. This, of course means a more efficient use of the propellant's power.

 

Splinter patterns from artillery shells is a complicated topic. It depends on the fuses, trajectory and the manufacture of the round.


The lethal splinter distance of artillery shells, especially modern ones, is much greater than for a mortar.

Circular lethal splinter patterns aren't always the most desirable. Artillery infantry co-operation was easiest in the world wars with highly directional shrapnel with inefficient large shrapnel balls. But it could be fired reliably to burst over the heads of advancing troops neutralizing enemy 50 ahead.

 

We're good, much respect for you and your opinions. In fact I am well pleased with the quality of the discussion, it's attracted some of the (IMHO) top tier rogues that specialize in factual debates, not trolling or arguing for the sake of arguing. I am please to have the honor to get to interact with each of you Harold's,Lwd, Sheldrake and K.B. Thank you.

 

I've been following the thread, but have little to contribute. I was a light machine gunner (M-60) by trade. But I do remember the maggots in weapons platoon complaining about how heavy the tube, base plate, bipod, ammo, etc were. We had the 81mm mortars since we were light infantry in Alaska. In the 82nd, we were equipped with the 4.2 (four-deuce) since the entire company (CSC, or Co. D- Combat Support Company) was all jeep mounted.

 

Humping the M60 was just as bad as humping the 60mm mortar, you had tripod, T&E mechanism, spare barrel bag and butt loads of ammo. I'm glad I was never in the battalion weapons company, the base plate for the M29A1 81mm mortar was a beast weighing 48lbs (the entire system weighed close to 100 lbs. and each HE round was close to 10 lbs. IIRC 9.6 lbs each).