Some real-life data on artillery fire adjustment

[tss]

Some time ago I found an old Finnish artillery doctrine manual ("Kenttätykistön ampumaohjesääntö") from an old book's shop. I haven't had time to read it completely, yet, but I've found some interesting tidbits. The doctrine was written in 1935 and the book was printed in 1936.

The book has one chapter on changing fire from one target to another. According to it, fire can be transferred to another target without spotting or calibration rounds if two conditions hold:

1) The range to the new target may differ from the range to the current target by at most by 1/3. (Formula given: If D_1 is the current range, targets within range 2/3*D_1 - 4/3*D_1 are allowed).

2) The difference on firing directions may be at most 300 "piiru"s. I don't have slightest idea what is the correct English term for piiru, but 300 of them make an approximately 17.5 degree angle.

In practice, the allowed change area is roughly a circle with radius 0.3 of the range (it is actually a band of a sector but a circle is a convenient abstraction here). So, if the guns were 2 km away, the maximum target adjustment would be about 600 meters. Obviously, this formula doesn't function for very long ranges, but the manual doesn't say what is the cutoff point. I recall that another source stated that fire missions without spotting could be fired up to half of the maximum range of the gun so that is a good guess for the upper limit of the formula. For a 76K/02 (the main gun when the manual was written), half range would be about 4000 meters, and for 122H/09 (the main howitzer) 3700 m.

Also, the minimum allowed fire adjustment is given as 4r, where r is the expected standard deviation on the displacement of a single round. A rough guideline would be that in usual firing conditions r=20-25 meters, so no fire adjustments smaller than 80-100 meters were allowed.

Another book, "Upseerin käsikirja" ("Officer's Handbook"), that was written in the same year gives time estimates for different artillery things. The most interesting are:

Deploying a forward observation post: 15 minutes.

Registering a new target: 2-3 min.

Calling fire without target coordinates: 4-6 min.

Calling fire with target coordinates: 5-6 min.

Calling fire to a registered target: 1.5-2 min.

Calling fire to a pre-aimed, registered target: 0.5-1 min.

Adjusting fire: 1.5-2 min.

These values are for light artillery and the book simply states that heavy artillery is a little slower. Also, if morse codes have to be used to transmit the fire commands, the calling times increase by 1-1.5 min.

The figures above are from pre-war regulations and may or may not correspond to actual reality of war. Also, Finnish artillery accuracy was among the best of the war, at least it was better than German or Soviet (this claim is partly based on opinions of several German artillerymen who fought in Northern Finland). I don't know how it would compare with British or US artillery.

Oh, and in case that someone wonders. The difference between spotting and calibration rounds is that with spotting rounds you try to bracket some target by firing alternate long and short shots until you are confident that you have the range correct. With calibration rounds you fire a number of rounds using the same gun settings and then observe where they land.

- Tommi

[Triumvir]

tss,

If I'm not wrong, the piiru is probably analogous to a true mil, the heavy ordnance way to divide up a circle. Depending on whom you use as a guideline, the mil is either 6000, 6283 or 6400 mils to 360 degrees.

Mils are used to shorten calculation for firing angles etc, and are short for milliradians. For more information, see http://boomershoot.org/general/mils.htm

[ntg84]

NT, sorry

[This message has been edited by ntg84 (edited 12-18-2000).]

[Forever Babra]

A mil is a one unit rise over a thousand unit run, hence the name. I haven't done trig in a few decades so I'll let someone else figure out if that is analogous to a "piiru".

------------------

"The whole of Scotland will rejoice if the commanding officer of the Canadian Army could see fit that the taking of Saint-Valery is accomplished by the Highland Division. I am sure that the 2nd Canadian Division will attend to Dieppe satisfactorily."

-- General Sir Bernard Law Montgomery, Aug. 20, 1944

[Triumvir]

Babra,

uhhh, yes it is. But the question for a piiru isn't whether it's a mil; it's whether it's a true mil, a Soviet mil or a US mil. I'm willing to bet that it's a true mil, because 300 "piiru" doesn't give a nice round number.

Again, a true mil is a milli-radian and the other two are simplifications for calculation. Having done some of this calculation myself (though very very little), the 1/6000 mil seems a lot easier to use, though of course less exact.

[Forever Babra]

Some basic math tells me a Piiru is a true mil. Based on tss's statement "300=approximately 17.5 degrees", I come up with 6171 in a circle. Smaller than the US/Nato 6400 and larger than the Russian 6000. Close enough to the 6283 true.

I've been hunting high and low for over ten years for a good Silva Ranger graduated in mils -- they just can't be found on the civilian market.

------------------

"The whole of Scotland will rejoice if the commanding officer of the Canadian Army could see fit that the taking of Saint-Valery is accomplished by the Highland Division. I am sure that the 2nd Canadian Division will attend to Dieppe satisfactorily."

-- General Sir Bernard Law Montgomery, Aug. 20, 1944

[Topi]

I think nowadays the "piiru" used in the Finnish army is 0.06 degrees, so full circle (360 degrees) is 6000 "piiru"s. (At least the finnish army www-site agrees. I really should remember this better But it might well be that we have, at some point, changed the definition to make the math easier. Most of the Finnish arty equipment is either Russian or Finnish made, so it makes sense that we are using the russian definition. (Firing with howitzer's cyrillic lettered direct fire sights would be even more fun if the "piiru"s were different..)

Topi

[tss]

Topi:

I think nowadays the "piiru" used in the Finnish army is 0.06 degrees, so full circle (360 degrees) is 6000 "piiru"s.

The 6000 "piiru"s to 360 degrees system was in ues already during the WWII. However, the manual states that a true "piiru" would be a little smaller but that in practice 6000/360 is close enough.

Firing with howitzer's cyrillic lettered direct fire sights would be even more fun if the "piiru"s were different..

There were also weapons using different "piiru"s in Finnish army. In particular, the guns without recoil systems that the French donated (87 mm and 150 mm guns) used the French system of 6400/360 (or 6200/360, I can't remember for certain).

There was a nice anecdote in the book "Vienan tykit" about the heavy 150 mm French fixed-mount guns. An additional difficulty in aiming those guns was that the gun had to be aimed by turning the whole gun. This also ment that the corrections had to be issued as mirror-image, so that to get the rounds to land to right you actually moved the end of the gun to left.

Once the guns of one such battery were directed by a forward observer of a different unit that used the common system. The first rounds were a little off so he issued corrections. When the telephone operator relayed the corrections the battery officer translated the figures in his head (he had a lot of experience doing it by that time, since even their own FOs used the normal system) and shouted them to the firing unit. However, the forward observer also heard the correction and got very angry because he thought that some joker was messing with his orders.

Now, I would like to clarify my original post a little:

Also, the minimum allowed fire adjustment is given as 4r, where r is the expected standard deviation on the displacement of a single round. A rough guideline would be that in usual firing conditions r=20-25 meters, so no fire adjustments smaller than 80-100 meters were allowed.

This was true only for spotting rounds. If the forward observer noted that the barrage was not right on target, he could issue also smaller corrections, in integer factors of r.

The rule of thumb was that if 75% rounds fell in front of the target, the aim point was 1r off the target, if 100% were short, the aim was at least 4r off. I can't remember the percentage figures for 2r and 3r adjustments.

The interesting point was that with timed fuzes the actual aim point should be 1r behind the target because that way the actual target gets higher concentration of shrapnel.

- Tommi

[Jeff Duquette]

I know this probably well known to the above posters on this thread. I figured I would just throw this out to clarify what the hell a mil is in normal people terms. 1mil equates to a length or height of about 1 meter at a distance of 1000 meters. At 2000 meters 1 mil equates to about 2meters in height or length. At 500 meters…that's right you guessed it…1mil at 500 meters equates to about 0.5 meters.

Mil relationship is a handy way of estimating range to a target. If you know the approximate height of a target, or its approximate length, you can estimate the range to the target using a mil relationship. So if you know a T34 is about 7 meters long (or whatever the actual length is) and your looking through your handy dandy set of military binoculars that are equipped with a mil scale on one of the lenses…you simply count the length of the T34 in mils. If the T34 is 7 mils long you know the range is about 1000 meters. If look through your binoculars and see that the T34 is 14 mils long, you know the tank is about 500 meters away.

Regarding the 6000 or 6400 mil relationship: Most NATO Armies use the 6400 scale. Soviets used a 6000 mil relationship. I'm just guessing here, but the Finnish Army I believe used\uses a 6000-mil relationship. Perhaps the Finnish scale was somewhat motivated by use of Soviet Equipment? You reckon the Syrians, Iraqis, and maybe the Egyptians use a 6000 mil relationship?

Digging through some historical stuff I came up with:

Whermacht used a 6400 scale (from "The Tigerfibel")

US ARMY in WWII also used a 6400 scale (From the April 1943 version of FM17-12)

Anyone know what the WWII Japanese Army employed?

[Guest JonS]

Hi all,

further to explain the use of 6400 rather than the 'true' value for mils...

6400 can be halved several times and still give nice, round numbers. eg, half a circle is 3200mils, quarter of a circle is 1600 mils, 1/8 of a circle is 800mils (this corresponds to the sub-cardinal points of NW, SW, etc), 1/16 of a circle is 400 mils (NNW, WNW, WSW, SSW, etc), and so on.

Using 6000 mils doesn't have quite the same simplicity.

Also, (shameless plug here) there is an article on mils at the CMHQ site under 'articles' --> 'General Military Interest'

Regards

JonS