How does a mortar work?

[Krautman]

Well, you drop the grenade into the tube, it goes 'plop' and the grenade comes out again... that's about all i know...

Since these things are so useful in cm, i just had to ask.

[stikkypixie]

Do a search on www.wikipedia.org, I can't give you the link because there is a problem or sumfink, BFC fix or do sumfink!

A little excerpt:

A mortar is a portable muzzleloading cannon that fires indirect shells at low velocities, short ranges, and high arcing ballistic trajectories. All of these attributes are in comparison with the mortar's larger sibling, artillery, which fires at high velocities, long ranges, and low arcs. Typically a modern mortar consists of a tube into which is dropped a mortar shell onto a firing pin resulting in the detonation of the propellant and the firing of the shell.

Btw Can anyone give me a definition for "support weapon".

[Robert Olesen]

Good question. I guess the shell has to be propelled by an explosion in order to travel as far as it does - but it doesn't seem to be a big/loud one. I have never been close to a mortar while it fires off shells.

[Joachim]

A support weapon is a weapon that is used (mainly) by troops which support the attack but do not actually take part in the attack into the enemy position. Once an objective is taken, the support wpns may follow up.

IE a HMG will deliver suppressive fire during the attack, but the crew won't be a part of the first wave.

Gruß

Joachim

[jthomas]

Originally posted by Krautman:

Well, you drop the grenade into the tube, it goes 'plop' and the grenade comes out again... that's about all i know...

I was a medic in an infantry batallion many moons ago... let me assure you that the "plop" or "thunk" you hear in the movies is BS. My experience was with 81mm and 4.2in mortars, and believe me- they can be LOUD. Nothing like a howitzer (I spent about 6 years in a FA Bn with M109A1's), they sound a lot like a really, really huge door slamming-hard. It also depends on the number of charges being used (think range- more charges, shoot farther given equal elevation).

I have found that many of the "sound effect" eplosions, muzzle reports, etc. are not really all that great. I don't really know why. Maybe because after the first salvo or two your eardrums are hosed.

[cmfan]

Hey Krautman,

I was a mortar man in an armored battalion in the U.S. army a few years ago. I think I've fired every type of mortar currently in the inventory of the U.S. army (60mm, 81mm, 4.2 inch and 120mm).

I think the descriptions everyone has given you so far are fairly accurate. To be a little more specific, a mortar usually consists of three basic elements:

the gun tube - this is the part of the mortar system which actually fires the shells. Its muzzle loaded, usually smoothbore (except, for example, the 4.2 inch mortar) and has a firing pin at the bottom which sets off the propellent charge on the shell.

the bipod assemply - resembles, somewhat loosely I suppose, a camera tripod with two legs. The bipod assembly attaches to the gun tube proping it up. It usually has shock absorvers and it is the element of the mortar system that is used to adjust the mortars aim (traverse, elevation, etc.)

the base plate - is a more or less a flat metal plate into which the base of the gun tube fits.

jthomas is completely right when he states that "plop" you hear in movies and even cm is bs. Even the relatively small 60mm mortar gives off a very healthy boom when fired. To me the 4.2 inch and 120mm mortars always had a metallic ring to them when we fired them.

jthomas -- what unit did you server in? when I saw your post I got flash backs to my platoon's own medic. Our platoon sergeant usually made him hang out over by the FDCs when we are at ranges, but once in a while we snuck him over to a gun and let him drop a round or two

[jthomas]

Originally posted by cmfan:

jthomas -- what unit did you server in? when I saw your post I got flash backs to my platoon's own medic. Our platoon sergeant usually made him hang out over by the FDCs when we are at ranges, but once in a while we snuck him over to a gun and let him drop a round or two

HHB 1/178thFA, 218th Mech Inf Bde (back then it was a round-out Bde for the 1st ID), before that HHC 1/118InfBN, 73 Inf Bde (Sep)

I usually got to fire a few rounds now and then . Usually our company commanders insisted on the medic continually making the rounds of the gun crews making sure everyone had enough water, aspirin, bandanas, and the like. It wasn't glamorous, but it's what I did. Inexchange for the "customer service" the gun crews would generally let you send a few rounds downrange.

[Krautman]

So mortar grenades are actually self-propelled, they contain the charge that blows them out of the tube? And how do you aim with it? Tube angle for the range(since propellant is always the same?), i guess, but what about the facing (azimuth you call that iirc)? Is there some device that exactly tells you which direction the tube is facing to, so you could re-adjust after changing the target?

[YankeeDog]

Answers to most of your questions depend on the mortar in question. In general, the lighter the mortar, the simpler the sighting and aiming devices. Some of the WWII-era 50mm mortars had little more than simple graded dials that read out the angle of the tube and the traverse, and aiming was done by rule of thumb and adjusting off of spotting rounds. The really light mortars also generally had one propellant charge in the base of the grenade, and that was it.

Most heavier mortar bombs have a base charge, as well as additional optional propellant charges that can be added to the base of the bomb to increase the range. This is why you will often hear commands to a mortar crew given as something like "Prep 4 HE, quick, charge 2" - the "charge 2" denotes the number of propellant charges.

As far as aiming, as you've guessed, tube angle + charge (and some math, of course) gives you range.

With bearing, once the mortar is pointing in the right general direction, the bipod can be traversed from side to side a bit to allow fine aiming. There is usually a small optical sight attached to the bipod that allows you to sight in the direction the mortar is facing.

With light mortars being fired at nearby targets (CM's on-map mortars), aiming is done by simple LOS and dead reckoning, either by sighting in directly on the target, or using a stationary object of known bearing that can be seen through the sight as a reference point. When mortars fire from a prepared battery position (CM's off-map mortar batteries), the battery position usually prepares a couple of aiming stakes to serve as points of reference for sighting -- these are the tall, red-and-white striped poles you often see placed in the ground near mortar/gun positions. This is very similar to the process that is used for larger guns.

Cheers,

YD

[cmfan]

What YankeeDog said

To add a little to it:

Yes, mortar rounds have what are called charges attached to their base. Most look like dohnuts wraped around the base of the round. Others, like on rounds for the 4.2 mortar look like Kraft cheese slices. Range on a mortar can be adjusted through either adding or removing charges, or by adjusting elevation on the bipod. Different mortars tend use one of these methods more than the other.

When you drop a round in a mortar it slides down the tube until it reaches the tube's firing pin. The pin hits a striker in the base of the round igniting a built in charge , which in turn ignites any additionaly charges attached.

Aiming--

Its all a combination of ballistics and geometry. First off... All mortars can technically be aimed directly by the gunner (e.g. the gunner directly sights the target). However, this method will probably get you killed as not many enemy forces enjoy having mortars fired at them.

What most mortar squads will do is find themselves a nice firing point outside of enemy observation... in a land depression, behind some woods or a hill. Remember mortars are high-angle weapons so you can fire them over obstructions. The mortar goes into "action" at the firing point (meaning it gets setup) facing the general direction of fire. It is then more precisely aimed using an aiming circle, a device very similar to land surveyors level with a precision compass built in. 60mm usually forgoe this. Once an initial direction of fire is established aiming stakes are deployed. These are used as stationary reference points from which to make aiming changes. All this happens, depending on the size of the mortar, from under half a minute to a couple of minutes.

As YankeeDog notes different caliber mortars vary in operation, but this is the general method of aiming them.

jthomas -- 1/67ar 2AD (before it became the 4th ID).

[jthomas]

Originally posted by cmfan:

jthomas -- 1/67ar 2AD (before it became the 4th ID).

It's kind of depressing, actually. I suddenly realized I've been OUT longer than I was IN! Growing old sucks, but it beats the alternative.

[old man rant ON]

I have to admit I have lost track of the Army's organization structure. The 23rd mech is now the 3rdID, and so on, so I have trouble keeping up with who is who. I used to know which division was headquartered where, and all the new infantry weaponry that I see being used in Iraq and I didn't even know they were in development! And since when do soldiers require KNEEPADS?... I've wandered off the topic a little, maybe that's a good topic for another thread. But oh, well......the boys today sure know how to kick butt!

[Dawg Bonz]

Thanks for the Mortar education.

The ‘Tips & Tricks’ thread on Mortars & Hard targets was good info as well. I never got a response to my questions there so here they are again.

What are the typical 'hang times' for different size mortar rounds?

Playing a QB in the open desert and I got @ 9" 'hang time' = time till impact, on a 3" mortar at @ 400 meters. Is that about right?

You have described the launch noises but what do you hear (prior to impact) of an incoming mortar round … assuming you are not impacted? Not complaining but the ‘Puff’ in CM seems a bit muffled.

What are the typical sizes of the Iraqi mortars now in use? On TV news reports some ‘insurgent’ mortars look very large = taller than a man!

Thanks.

[YankeeDog]

Don't know about hang times; obviously the answer is going to depend on the charge(s) used. @400m, a 3" mortar would be using minimum charge. . . you can calculate the hang time off of the muzzle velocity + launch angle (and 9.81 meters/sec acceleration due to gravity), but that's more math than I feel like doing right now.

I've heard that one of the more insidious things about mortar fire is that the "incoming mail" sound is much quieter and briefer than it is for gun artillery. Fortunately, I've never actually been under a mortar barrage, so I wouldn't actually know, though. . . I've heard it described as a sort of whooshing whistle (how's that for vague!!).

As far as the Iraqi mortars, most of Hussein's military equipment was of Soviet Block origin, and obviously a lot of that equipment has fallen into the hands of the insurgents. The large mortars you saw were probably 120mm -- I have seen clips from both Iraq and Afghanistan of Soviet 120mm mortars.

Cheers,

YD

[Dawg Bonz]

Thanks YD.

I wondered about the "incoming mail" sound. A Viet Nam Veteran told me that you did not have much of a sound signature with incoming mortar rounds. Your ‘whooshing whistle’ sounds about right. The CM game mortar sounds just seem a bit muffled to me.

Dawg

One wonders how a few guys quickly move, set up, fire & "hide" a 120mm mortar in city streets?

[athkatla]

As a former Mortar Fire Controller (MFC) in the British Army I can add a little to this discussion.

'Hang Time's' or Time of Flight as we knew it, depends on the range you are firing at, and of course the number of propellant charges attached to the base of the mortar round. Once the MFC had ordered an adjusting round to a target, the Command Post Operator(CPO) on the Mortar Line, would send over the radio, "Shot 1, 22", indicating that the Number 1 mortar was the mortar firing and that the time of flight was 22 seconds, this of course was so that the MFC knew roughly when the round was about to land so he could observe it for adjusting.

I may be a little rusty, as I left the Army 21 years ago after serving for 14 years but we were then using the 81mm Mortar and the highest charge we could fire then was charge 8 with a range of approximately 5.5 - 6 K's (if I remember correctly).

The MFC would provide the target information for the Mortar Line by means of a 8 figure grid reference and a Direction to the target using a Compass. The order would be something like,"Hello 51 this is 51A, Fire Mission 2 Mortars, Grid 364284 Direction 0200 Adjust Fire, Over", this exact message would be repeated by the CPO back to the MFC over the radio, so that the MFC knew he had the details correct.The CPO's radio message would be, "Hello 51A this is 51, Fire Mission 2 Mortars, Grid 364284 Direction 0200 Adjust Fire, Out.

The CPO would then plot this information on his plotter board, (probably replaced by a computer now) and then issue his orders to the Mortar Line. The whole Mortar Line would lay their Mortars to this information, and ready the rounds to fire, and when they reported they were all 'on' he would usually order the Number 1 Mortar to fire. As I remember, the 81mm Mortar was laid on targets using the C2 sight, a detachable sight that, IIRC was also used on the GPMG in the sustained fire role.

Oh well, it's early morning here in the UK, and I guess I was reminiscing, I loved my days as an MFC, and just writing those radio orders down brought back many happy memories, oh and yes, the noise when you fire a Mortar is very loud. Before qualifying as a MFC, you must also be a qualified Mortar Man

[cmfan]

Wow, there are quite a few people that have been around mortars on this board!

Not much to add except that most mortars are fairly easy to transport. A 60mm can easily be carried and employed by a crew of 3 (or less depending on the system).

The 81mm variety is also somewhat man portable -- though your not going anywhere very fast. A single person can even cary the tube. Barring that, an entire gun system could easily be carried in a pickup truck or even passenger car.

Compared to the old 4.2 inch mortars, the new 120mm mortars are realtively light -- though not generally considered man portable. I'd say two people could carry the barrel for short distances if they had to. Same for the base plate. I know I've seen footage of Rangers using a special cart to lug one around.

Its actually not very surprising that insurgents in Iraq are able to move and deploy them so quickly. It's what most mortars are designed for.

--

Can't say I've been on the receiving end of mortar fire, but I've met people who say you don't hear much until they hit. I have been under the flight path of 155 artillery (again, thankfully not at its impact point). Sounded a little like a fast moving jet flying overhead.

[athkatla]

Originally posted by cmfan:

Wow, there are quite a few people that have been around mortars on this board!

Not much to add except that most mortars are fairly easy to transport. A 60mm can easily be carried and employed by a crew of 3 (or less depending on the system).

The 81mm variety is also somewhat man portable -- though your not going anywhere very fast. A single person can even cary the tube. Barring that, an entire gun system could easily be carried in a pickup truck or even passenger car.

Compared to the old 4.2 inch mortars, the new 120mm mortars are realtively light -- though not generally considered man portable. I'd say two people could carry the barrel for short distances if they had to. Same for the base plate. I know I've seen footage of Rangers using a special cart to lug one around.

Its actually not very surprising that insurgents in Iraq are able to move and deploy them so quickly. It's what most mortars are designed for.

--

Can't say I've been on the receiving end of mortar fire, but I've met people who say you don't hear much until they hit. I have been under the flight path of 155 artillery (again, thankfully not at its impact point). Sounded a little like a fast moving jet flying overhead.

I too got a close look at an arty shell approximately 200 metres in front of our Spartan when parking up on an OP on Hohne Live Fire Range in Germany. We had just pulled up and opened the hatches when this round hit the deck, can't say we heard it coming, just heard all the **** hitting the Spartan as we hurriedly closed the hatches just in case they decided to drop another one a little closer. Bloody long range snipers!

Needless to say, there was a Range Check Fire and we never got to send a Fire Mission till the next day.

[Dawg Bonz]

Thanks athkatla & cmfan for the 'Time of Flight' & move and deploy info. I guess those 120mm mortars are lighter than I thought.

RE: the receiving end of mortar fire. How difficult is it to spot a mortar team? Say you have a long 15" 'Time of Flight' and little launch sound signature at a distance. How hard is it to spot the mortar teams at distance?

[cmfan]

Well, I'd say visually spotting a mortar crew doing their thing depends on how good that crew is and what type of mortar your talking about.

A 60mm mortar has the shortest range, so its usually employed closer to the enemy than other mortars. However the 60mm also has the smallest fire signature and can be easily moved. Crews can essentially do a "shoot and scoot". Run out, setup the mortar in a couple of seconds, fire off a few rounds and then displace.

The same applies to other mortars to a lesser extent. Also remember that even an 81mm mortar has a range of several kilometers. A crew doesn't need to be close to the front lines to be effective. Add to that the fact that you can fire a mortar from behind a building, hill or in a trench...and crews can camouflauge their postion, its down right hard to visually spot a good mortar team doing their thing.

One factor you do have to watch out for though is counter battery radar -- don't think this existed during WWII. Since the mortar round has such a high ballistic parabola and is relatively slow its fairly easy for counter battery radar to figure out the firing point of rounds flying through the air. That's were the portability of mortars comes in handy. Fire a couple of fire missions and then scoot to a new position.

[Dawg Bonz]

Thanks cmfan. Sounds like a tight & fit mortar crew could be some folks worst nightmare. Some news reports did note US forces counter battery radar is used to spot insurgents with mortars in Iraq. One problem is insurgents fire a few rounds and split to leave an IED or RPG ambush for the patrols heading for the counter battery ID spot. One fellow said, "If we go looking and the streets are empty ...it is really quiet.. sumpin is going down."

[Other Means]

I've seen many pictures of mortar rounds & many tubes but i don't think I've ever seen one of a round with the propellant attached. does it get dropped down the barrel separately or it it attached to the base?

does anyone have a picture of one?

thanks.

[Cpl Steiner]

Hi,

This thread reminded me of that scene in "Saving Private Ryan" when they bang mortar rounds on a mortar base plate to arm them and them chuck them by hand at the enemy. Does anyone know if this would have actually worked, or is it out of a script writer's imagination?

[YankeeDog]

Definitely works; the SPR episode is actuallly probably inspired from a RL Medal of Honor event -- unfortunately, I can't remember the name of the recipient off hand, but I believe it took place in Italy.

As far as the propellant charges, with modern US 81mm mortars and many others I've seen, the extra charges attach to the base of the bomb. I don't know if this is the case for all mortars, though.

Cheers,

YD

[Dandelion]

These are postwar pieces but I couldn't find any other decent picture on the internet. The arrow aidingly points at the Teilladungen, the extra propellant charges mentioned above, of which you ask. This is how it looked on German mortar rounds (except 5cm, which had non-adjustable propellant)

German mortarshells had a Grundladung, an inherent propellant charge in a tube inside the finstabilised "neck" of the shell, to which the ignitorwas fastened at the bottom. As the shell slid down the barrel, it hit a firing pin at the bottom, igniting the propellant charge much like the hammer of a revolver ignites a standard cartridge, and with the Grundlagen would go off any Teilladungen added such as those above.

On the GrW 42, there was also the option of setting the ignition to mechanical handling instead, with the shell remaining in the barrel until manually triggered. For which purpouse there was a safety mechanism.

You see the same thing here, with the actual 12cm Wurfgranate, but here the extra propellant is depicted separately (up in the right corner). In the lower right corner you can see the ignitor at the bottom (the centre ring on the "base stamping" figure).

And you see the same things here, in DDR use (this is the GrW 34 postwar munition).

Cannot recall the scene so I cannot tell what it was that they did. Detonating the ignition would be an extremely bad idea if still holding the shell in your hand, the Grundladung would go off. Unless removed, in which case there is not point in hammering the shell against the baseplate, as the ignition was part of the Grundladung.

Even if they managed to arm the shell, Germans would normally use Rückstoßladung with 8cm mortars, meaning the shells bounced and then detonated 1-5 meters up in the air. Would take a powerful hurl to recreate the bounce, and would seem like a bad idea to be around if one succeeded.

But, being no mortarman, I'll not be the one who says its impossible.

No super pics there but I hope they give a general idea.

Cheerio

Dandelion

[cmfan]

I'm highly skeptical of that scene in "Saving Private Ryan".

All mortar rounds I know have a built in amount of propellent inside the base (the narrow tube like area from which the fins protrude). Depending on the round this propellent can be the equivalent of a full charge (60mm mortars) or simply a shotgun shell's worth of powder (4.2 inch mortar I believe).

When a mortar is dropped down the tube it slides down until its firing cap, located at its very base, strikes the mortars firing pin. When this happens the built in propellent is ignited. This in turn ignites any additional charges attached.

Having pointed this out, it goes without saying that removing a mortar round's safety pin and then proceeding to slam its base against the ground, particularly while holding it with your hand, is probably a bad idea. Its also important to remember that removing the safety pin/lock off a mortar is not the only step necessary to arm its fuze. The round has to usually spin a few times or be subject to sudden jolt before the fuze goes active. Simply throwing a round is unlikely to set it off even if its safety has been removed. I imagine this is why the writers in SPR might have had the actors hitting the rounds against the base plate. They simply forgot or ignored the fact that this would have also likely ignited the base propellant. Lastly, a 60mm mortar has the explosive power of several hand granades. I know they were standing in what looked like a crater, but I still doubt that they would have been able to throw the rounds far enough not to be injured by their explosion.

Still... I do have to admit my knowledge of mortars and their ammunition is limited to what is currently in the U.S. inventory. Perhaps the rounds being modeled in the film were of a variety particular to that time period -- and particularly unsafe at that.