Aiming Stakes

R. Lee Ermey does his thing interviewing some Marine 81mm mortar gunners. It’s nice that they give a bare bones explanation of the use of aiming stakes for fire control. I’ll let Esli chime in later when he gets around to commenting. He’s the local subject matter expert on mortar fire control.


12 thoughts on “Aiming Stakes”

  1. Ahh, 1995, “Hill Week” at the Infantry Mortar Leader’s Course… Aiming stakes, in a nutshell, give the gunner a constant reference point at which to aim the mortar sights to control the direction in which the mortar round flies. You want to aim at a target to the left of your current point of aim, you crank the sight around the correct number of mils and shift the tube to the left or right as necessary, and re-align the sight reticle with the aiming stakes and the round will go where the fire direction center (FDC) wanted it to go.
    If you want technical, keep reading… When you occupy a mortar firing point, you align the guns on a Direction of Fire (DOF) by putting the guns generally on a straight line through the base plates. This line is perpendicular to the DOF. (So, if your DOF was north, your mortars are all arrayed on an east-west line.) You then use an aiming circle which is essentially like a surveyors tool. Using the magic of geometry (the only time I ever did after high school), you use the aiming circle and the mortar’s sight to ensure that the mortars are exactly parallel to each other. Once the guns are set, each crew places out aiming stakes at a distance of 50 and 100 meters. All mortar crews put them out on the same parallel lines, which are perpendicular to that imaginary line on the ground that runs through all of the mortar base plates. The direction from mortar sight to aiming stakes will be called some constant mil direction such as 3200. (Recall that a circle has 6400 mils in it, 17 of which equal one degree.) This direction is arbitrary but standardized, and does not correspond to the actual compass reading of 3200 mils (or whatever mil direction you choose.) Now the FDC uses mil directions (referred to as “deflection”) to give commands to the gun crew. If your target was exactly on the gun-target line that the stakes were set out on, the FDC would announce “Deflection 3200”, the mortar crew would align the sight reticle with the aiming stakes, and the round would fly along that direction when fired. (You control range with elevation of the weapon and varying propellant charges). So, now let’s say our mythical target has shifted to one side by 50 meters. (Recall that one mil subtends a distance of 1 meter at a range of 1000 meters, 2 mils at 2000 meters, etc.) So if our target is 1000 meters away, you would need to shift the mortar tube to the left or right by 50 mils to shift the impact of the round 50 meters. So, the FDC is going to announce a new deflection “Deflection 3150” or “Deflection 3250” depending on which way the target had moved. Now the mortar crew puts the new deflection on their sight and moves the mortar tube until the sight reticle is once more aligned with the aiming stakes. The 50-mil angle induced by the gunner cranking the new deflection on the sight is the same 50-mil difference that will move the round 50 meters to the left at a range of 1000 meters.
    Since all of the guns were laid parallel to each other the mortar rounds will all burst on the far end at the same distance apart creating a “parallel sheaf.” To get really cool, if you are firing at a small concentrated target, you can compute and fire a “closed sheaf” where there is a difference of a couple mils in deflection placed on each gun which results in all rounds bursting at the same burst point. Or, you can do the opposite and create an “open sheaf.”
    Simple, no? This is why the mechanized mortars now have the Mortar Fire Control System, which lays the guns and computes firing data without aiming stakes. It is the mortar variant of the Paladin to the artillery community: all digital and computerized. When it works….

    1. Thanks. That was what I wanted, but didn’t want to look stupid and say “How the hell would I know, I never hung out with the mortar platoon?”

  2. Good article. I’ve often been amazed about how quickly and accurately mortar support can be had in combat. Being former USAF I never had occasion to use a mortar (probably a good thing), though the first thought that came to mind was E.B. Sledges descripion of mortar use in his book, “With the Old Breed…”.

    1. I should just note that the smaller the mortar, the less the need for such involved fire control. Light infantry quite often will carry their 60mm mortars on patrols. The 60mm mortar can be fired from a baseplate and bipod, with the same aiming stakes method, but it also can be fired from a small baseplate in a handheld mode, aimed by little more than Kentucky windage. The aiming stakes method is needed when the mortar crew cannot view the impact area. But during a dismounted patrol, the 60mm crews can often achieve quite good accuracy just by “guesstimating” their aim over short ranges. They can shoot at targets as close as 75m this way. For the larger mortars, this isn’t really an option. But when they are in a defensive position such as a combat outpost, they typically have several targets already selected, and can fire on them immediately, and then shift from there to more accurately engage the attackers.

  3. With my mortar platoon (6 x 120mm mortars in M1064 tracks), I could get a call for fire WHILE ON THE MOVE and within about two minutes get rounds out of the tube. In the defense, maybe 45 seconds. In both of these cases, the majority of time comes from computing the firing data, while it takes a matter of seconds to get the guns laid. Mortars are the fastest and most responsive fire support asset on the battlefield. (Unless you have attack helicopters already on station.)

    1. Sounds like old style field artillery. Battery comes up, guns unlimber, horses and limbers move to the rear, load and fire guns twice, limber up, and be back on the move in two minutes. But all line of sight work.

      Of course, those things weigh 1800 to 2200 pounds and take a crew of 7, plus drivers, and Chief of Piece.

  4. It does sound similar. The fire mission is called a “hip shot.” It comes in while you are on the move. The FDC gives a heads up, all tracks stop moving. The FDC computes a direction of fire, and all tracks pivot steer until the tube is laid on the appropriate direction of fire. You fire, by SOP, generally two rounds of HE. The guns were not laid with the aiming circle (just each squad leader with his compass), so there is some loss of accuracy as a tradeoff for speed, and you don’t put out aiming stakes unless there is going to be an adjustment. It is high adventure when it comes to mortar live fire training.

  5. Generally. When you are moving, it is because you are on the way from one firing position to the next, ergo, if you fire, it was not a planned mission. So, when a fire mission comes up on the fires net, the BN FSO makes a decision to send it to the mortars or to the FA firing unit. At that point, the mortars are much more responsive than putting the mission into the FA queue and immediate suppression or immediate smoke are common. If you want, or you anticipate a correction, you can throw aiming poles out and go into an adjust-fire process.
    Not to mention, with 120mm mortars, your effects on target are very nearly 155mm. My mortar PLT was an old 6-gun PLT with two FDCs, but they have reduced to 1 FDC and 4 guns (big mistake in my opinion).

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