Wednesday, March 20, 2013

Trevithick, You Ignorant Slut


I take just a wee bit of umbrage at this:

The mortar has changed little since World War II and remains one of the simplest weapons to operate, which is why it is found at the lowest level of infantry units, said Joseph Trevithick, a mortar expert with Global Security.org.

"Basically, it's still a pipe and it's got a firing pin at the bottom," Trevithick said. Still, a number of things could go wrong, such as a fuse malfunction, a problem with the barrel's assembly, or a round prematurely detonating inside the tube, he said.

 Am I qualified to speak to how "simple" it is to operate a mortar? Credentials time:

Well, let's see: I earned the "Golden Gunner" award -- perfect scores on the 60mm and 81mm mortar gunner's exams -- at Infantry Training School, Marine Corps Base Camp Pendleton, CA, 1986. I subsequently served for ten years and in every Weapons Company 81mm mortar billet  in the US Marine Corps, with the exception of forward observer, platoon sergeant and platoon commander (and those last two on a few brief occasions as "acting" and FO once or twice by way of familiarization training to learn to work with a Forward Air Controller on Suppression of Enemy Air Defense [SEAD] stuff).
English: M29 81mm mortar
English: M29 81mm mortar (Photo credit: Wikipedia)

I've been an ammo man, an assistant gunner, a gunner, a squad leader, a section leader, and chief of the Fire Direction Center (in that last role, I OJTed the plotter billet -- and in fact re-invented that billet by teaching myself the ballistics and trigonometry necessary to get a programmable calculator to handle some of the lifting in place of our warping old M16 plotting boards, since my unit didn't have money budgeted for the then-new Mortar Ballistic Computer). In 1991 in Saudi Arabia, myself and one other Marine (Corporal Gerald Pagan) were selected to familiarize the embryonic Saudi Marine Corps with the Vietnam-era M29 mortar, since he and I were the only two guys in the area who still knew it inside out (our unit had upgraded to the M252 a few years before).

So yeah, I think I know a little bit about mortars. More on their complexity after the jump.





A modern mortar is not just "a pipe with a firing pin at the bottom." It is a smooth-bore, high-angle-of-fire, muzzle-loading weapon system (including not just the baseplate, bipod and barrel ["cannon"], but a fancy-schmancy sight system and "aiming posts" used to orient it for fire at targets that are out of sight) that properly -- and most manifestly not "simply" -- fired, can put a variety of ordnance -- high explosive, white phosphorous, illumination -- downrange, accurately (to within a few meters) hitting targets as distant as 3500 (60mm) to 5500 (81mm) meters on the basis of communicated data rather than visual aiming.

Mortars can be used for "direct fire" -- fire at targets that are visible, just by aiming over the barrel, estimating the range, and giving them hell. The 60mm mortar in particular has a trigger mechanism (so that it can be loaded and then fired, instead of just dropping the round down the barrel and having it immediately take off), and a range indicator on the barrel so that the gunner can dispense with the bipod and just use his hands to manipulate the barrel. Don't try that with an 81 unless you want an arm ripped off -- use the bipod. I watched the aforementioned Corporal Pagan score a direct hit on a pipe (about six feet tall and maybe a foot in diameter) at about 800 meters once during a little impromptu range contest.

But the real strength of the mortar is putting rounds on targets that are out of sight, over a hill or whatever. And that is not by any stretch of the imagination a simple process. Here's how it works with 81s:

First, the guns have to be "laid." That is, eight guns all have to be put in a particular and known place, facing in the same particular direction. If you think that's simple, you're probably an experienced surveyor. I'll leave out the boring details about aiming circles, bore-sighting, accounting for the difference between magnetic north and grid north, etc. but just keep in mind that we're not talking about looking through a scope and pulling a trigger, here. It's a matter of determining your exact position on the surface of the earth and then arranging eight pieces of artillery in perfectly uniform orientation vis a vis that spot and some arbitrary direction (and working in NATO "mils" -- there are 6400 of them in a circle -- degrees aren't precise enough for this work) such that when they are aimed at their aiming posts with their sites set at a deflection of 2,800 mils, they are all aimed in the primary direction of fire. All of that takes a good deal of very not-simple work on the part of the Fire Direction Center and the gun crews (each crew is a "squad" with a squad leader, gunner, assistant gunner and two ammo men).

Before going any further, let me clarify something: All of this is being done down at the platoon level by grunts. "Real artillery" has a big rear-echelon infrastructure at the battalion or regimental level called the Fire Support Coordination Center. They have big boards covered with maps. They have computers. They have a crap ton of people figuring this stuff out. What the 81mm mortar platoon has is a Fire Direction Center chief, two guys with round plotting boards and pencils, and a communicator to accept fire missions over the radio.

So the guns are laid and ready for action. How do they know where and when to fire?

Well, a call comes in over the radio from a guy called a Forward Observer -- a mortarman who's out humping it with the rifle platoons and whose job it is to call in mortar fire when they need it. That call will specify the nature of the target, what kind of ordnance the FO wants put on that target, and the location of the target, given as a map coordinate. If it's a SEAD mission, there will also be some timing information, because the thing with SEAD is that the rounds have to stop hitting the target before one of your aircraft comes through, and start hitting it again as soon as that aircraft is out of their way. Which means that the FDC has to take into account the flight time of every round and the gun crews have to fire them at precisely the right times. But let's let SEAD go for now -- it's just one of the most complicated missions. None of them are simple.

So the FDC has a target location, ammunition type, mission type ("immediate suppression," for example, means "we're in deep shit, get that stuff down here NOW" instead of "send a round, I'll adjust, when we get it right we'll fire for effect").

At this point, the FDC has to find that target on the map and determine two things: Its exact direction from the gun line and its exact range from the gun line (the plotters have to agree on this information -- to within two mils with respect to direction -- or it gets calculated again until they do). And once they have those two things and have consulted the firing table for the lot of ammo being used, they have the three elements the gun line needs to fire: The deflection to put on the sight, the elevation to be put on the sight, and the charge to be put on the round (mortar rounds come with little "charges" of propellant; at less than maximum ranges, some of these are removed from the round before firing).

Once the deflection and elevation are dialed in to the sight, the mortar has to be moved so that it is pointed at the aiming posts, and it has to be made level. This, again, is not a simple process, but it gets done in seconds (the test standard for a large deflection change is 60 seconds, but that's insanely slow; the fastest I've done it myself is 12 seconds; the fastest I've seen is, again, Corporal Pagan at 8 seconds) with the gunner lifting and moving the bipod and/or cranking it left, right, up or down and the assistant gunner tapping him on the shoulders and verbally advising him as to which way he needs to go and whether the bubbles on the site are or are not level.

If the FO got the grid coordinate right, and if the FDC got the calculations right, and if the gun crews got the sight data set correctly and the mortars properly aimed and leveled, the guns are now aimed as they're supposed to be, and it's time to fire (on "immediate suppression," immediately, otherwise on command from the FDC).

But of course it's never that simple. Normally a round will go out and the FO will correct ("left 50 meters," "right 100 meters," "add 50 meters," "drop 100 meters," etc.). Once the rounds are falling where the FO wants them to be falling, he'll tell the mortar platoon to "fire for effect" -- all guns fire multiple rounds on the latest aiming point.

All of the above is the "simple" version. I didn't really go into SEAD much (it's some sphincter-clenching stuff), and I didn't even mention "converging the sheaf" (so that all the mortars are firing on the same specific point rather than just in parallel in the same direction), moving an active gun line in bounding overwatch, etc. "Simple," my ass.

Mortars aren't deployed at "the lowest level of infantry units" because they're "one of the simplest weapons to operate." They're deployed with the lowest level of infantry units (a 60mm mortar section in the Weapons Platoon of each rifle company and an 81mm mortar platoon in the Weapons Company of each infantry battalion) for two reasons:


  • Those "lower levels" of infantry need a measure of heavier ordnance that's at their immediate disposal rather than distantly located and dispensed at the convenience of higher headquarters; and
  • The 60mm and 81mm mortars are the only thing fitting that bill that are man-portable so as to be able to move with dismounted infantry.
Sure, a 155mm artillery round puts down a lot more heat than a mortar rocket -- if you can reach the people who have the 155s, and if they aren't busy with something else. A rifle company commander has his 60mm mortar section right there with him, and an infantry battalion commander has an 81mm mortar platoon that he can call on directly instead of having to run a request through regimental/FSCC red tape and hope his situation is not low on their list of priorities at the moment.

Oh, and one more pet peeve: You know how in the movies when someone drops a round, the mortar goes "bloop?" Um, no. An 81mm mortar round coming out of the tube will ring your bell.  It is a cannon, firing next to your head (if you're the gunner or a-gunner). A 60mm a little less so, but not just "bloop."
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