Tank and SP Gun Medium and Long RangeTargetting

[lazysack]

Just curious how they were able to fire accurately over distances.

Was it like the gun-sight of a rifle, where they just set the range(700m)and fired at whatever was in the crosshairs? How were they able assess how far away their targets were? Some sort of hand-operated range-finder binoculars?

How was it that they were able to fire effectively at targets 4000m away, as some German SP guns were able to do, according to the literature? Were the targets called in from the front-line units? Were there radio-sets in every tank and SP unit then? Were they only accurate as massed barrages firing at dense armour formations? Or could they actually see 4km away in some cases, like on the Ukrainian Steppes?

Any links/books that could help me understand?

Thanks for any and all comments!

[JasonC]

"Was it like the gun-sight of a rifle, where they just set the range(700m)and fired at whatever was in the crosshairs?"

There is a sight attached to finely graded dials. This sight moves independent of the barrel, but the offset of its movements is translated to offsets to a pair of small "levels". The sight's base angle is first aligned with the barrel, long before battle.

Then when the gunner puts his sight on a target, he has rotated the dials some definite amount, which translates to unlevel bubbles in small "levels" attached to the tube. When the barrel is traversed, and elevated or lowered, these bubbles move. You do that until the two bubbles, one for vertical and one for horizontal angle, align in their little "levels". They do so when the barrel has been moved through the same angles the gunner dialed in to his sight, to put his crosshairs on the target.

The effective fineness of the alignment, for a good crew or with time, is about half a mil. That is 1/12800 of a circle, and translates to an expected error of 2m at 4km range, left of right. A hasty gunner might experience twice that "pointing error". Understand, you will generally get some random placement within that range, so you might be 2m left, 1m left, dead on, 1m right, 2m right. That is still very fine aim.

"How were they able assess how far away their targets were?"

This was the main source of errors in aim, called "range probable error" in the trade. For short range targets it did not matter very much because the trajectory is flat enough, you are effectively "bowling" rather than "playing golf".

That is, if the rise and fall of the shell over its flight time is less than the height of the target, you don't care if your range is off by several hundred meters. It will only mean being high or low by a foot or two, and the target will be big enough vertically you can still hit it. Tank gunners could "zero" their sights for 1 km or so (test firing on a range, beforehand), and then hit anything (the size of a tank) that they pointed at between 500m and 1250m. The round is in the air only a second or two, so the trajectory is pretty close to flat.

With lower velocity guns and longer ranges, the flight time is much longer and the arc necessarily much less straight. A 400m/sec average velocity can mean 5 seconds to go 4 km for a direct fire shot, while a long range indirect shot can easily be in the air for 30 seconds. The first will rise and fall about 100 feet, the second on the order of half a mile. Definitely "golfing". So the range estimate becomes much more important.

For direct fire from SPA, many times they would just eyeball it for their first range estimate. The size of the target in the sight picture gave them some idea - if a tank, longways, goes 3 ticks on my sight reticule, the range is around x meters. These estimates could easily be off by 200 to 400m.

Some guns were provided with stereoscopic range finders, notably in German SPA units. These could give much better range estimates when used correctly.

For direct fire shots, the main way they dealt with range errors was by "bracketing". They fired the first shot and noted whether an explosion obscured the target (a short), or the target was sillouetted against the explosion plume (a long). Then they'd correct by up to 400m and try again.

Once they got one long and one short they'd split the difference and fire for effect. This procedure could rapidly get a round within 100m on the range axis. Half a mil elevation error can translate to 20m range error on the long axis, since 2m higher means longer to fall, at only the vertical velocity of the shell, which is much lower than how fast it is moving downrange. So closer than about 50m on the range axis wasn't worth trying to correct anyway. You just shot several times and counted on the height of the target, shot to shot variation, and near miss effects.

You can certainly see targets at 4 km if the terrain is open. Men would be tough if there were any cover, even with optics, but vehicles are visible. 4x power scopes were everywhere and some vehicles had up to 16x mag. To get a wide sight picture and scan a large area you have to use a lower mag - but if you pick up movement that way, you can train on it and then up the mag and see what it is.

As for called fire, the way that worked is by having the forward observor call out a location, by grid reference or by offset from a known terrain feature e.g. 400m west of the church steeple. Fire direction centers - which could be with each battery, or with a regiment or battalion artillery HQ - then translated that into angles for a battery, based on maps, protractors, plotted battery locations, and some quick trig (or table look up, to do the math only once).

The FDC then passed a fire order to a battery, in the form of a deflection (horizontal angle) and a quadrant (vertical angle), specifying the size powder charge to use as well (ranges for angles and charge sizes were recorded and looked up in tables). The battery put one gun on those angles and fired a single spotting round.

The observor then called the corrections, eyeballing how far the plume looked from his intended target, in meters (or yards) which were translated into mils at the FDC based on the range (e.g. "right 200m" for a 8 km shoot would mean right 2.5 mils), and then dialed it into the sights of the shooting gun. Once a round was close enough - 50-100m - the observor would call "fire for effect" and the whole battery fired on those angles.

There may have been slight differences from all of the above for any of the WW II armies. The above is how it works in the US Army artillery. I hope this helps.

[David Chapuis]

A 400m/sec average velocity can mean 5 seconds to go 4 km for a direct fire shot, while a long range indirect shot can easily be in the air for 30 seconds. The first will rise and fall about 100 feet, the second on the order of half a mile. Definitely "golfing". So the range estimate becomes much more important.

Is that a typo that should say 10 seconds (the part in bold)? Or is there another factor that makes that more complicated than meets the eye.

[JasonC]

No typo, right you are of course. Thanks.

For the total flight time. The shell only spends half of its time of flight falling, since it spends the first half ascending (approximately). So when you want to see how far it goes above vertical, you use half the overall flight time in h = 16 feet * t ^ 2.

[ October 02, 2003, 05:04 PM: Message edited by: JasonC ]

[lazysack]

Thanks Jason. Sounds pretty friggin' complicated!

It'd be neat if there was a decent WW2 tank sim I could try out to get the feel of it.. Anyone know of any good ones? Any on the horizon?

[Bruceov]

Panzer elite lets you determine range just like they did it in real life

[lazysack]

Hmmm... I'll look into it, thanks!

Doug

[rexford]

Things may be a little simpler than JasonC points out if one is talking about WW II tanks and guns.

With the Sherman 75mm gun sight, you line up the stationary target so it is in the middle of the scope markings from side to side.

Then you estimate range, where the average crew was able to be within 25% of the true range on about 68% of the guesses: errors range from 0% to about 100%.

88mm Flak and Nashorns may have used range finders.

The Sherman gun scope has vertical range markings, so if the range is estimated to be 750 yards one raises the gun until the middle of the target is about halfway between the 500 yard and 1000 yard lines.

It appears that the Sherman scope moved with the gun elevation.

If the shot falls short, one can use standard bracketing procedures or elevate the gun so the target is where the shot passed it on the scope (burst on target procedure).

With bracketing, if the shot falls long or short by about 200m one would add or subtract a set amount.

That is how it works in training, on the battlefield all sorts of silly errors come into play due to nervousness, fatigue, fumes, heat, yelling and fear. And other stuff, too.

If the target is moving across the line of sight, one tracks the vehicle by moving the gun with the target, jumps ahead of the target by the appropriate lead angle for the estimated lateral speed, and fires.

Note that a target moving straight at a gun does not require a lead angle, so it not very much more difficult to hit than a stationary target.

[Howard R]

This is great! I've always wondered about this stuff. Battlefront.com comes through again!

Would there be a difference in direct fire if the gun is firing HE vs AP? Would there be a difference for APDS vs. solid shot AP? How about the shaped charges that some larger caliber artillery could fire?

[JasonC]

Rexford is describing the procedure for typical tank guns, usually firing at 1.5 km or less. I was describing the procedure for SPA - like a M7 Priests or German Hummels - often firing at considerably longer ranges - 2 to 4 km direct, or up to 20 km indirect, and often in batteries of 4 to 6 guns.

Of course there are intermediate cases - some tanks dueled at 2-3 km. When they did they had the kind of equipment Rexford describes, but had to get it something starting to approach what the arty does.

As for the round used, there wasn't a large difference in how they were aimed. Of course with HE firing at soft targets, especially with multiple guns firing, you treat near misses as close enough and just fire some more. With all the AT round types, you obviously need a direct hit.

HEAT is no different in that respect. It doesn't lose penetrating power with range like kinetic energy AP does, but on the flip side it is more sensitive to (somewhat random) impact angle.

[rexford]

Originally posted by Howard R:

This is great! I've always wondered about this stuff. Battlefront.com comes through again!

Would there be a difference in direct fire if the gun is firing HE vs AP? Would there be a difference for APDS vs. solid shot AP? How about the shaped charges that some larger caliber artillery could fire?

If you're interested I'll scan some pages from the Sherman gunnery manual for 75mm ammunition and e-mail them to you direct.

The manual pages on range elevation for stationary targets, and lead against moving targets are short and to the point.

The tank manual for Shermans directs the crew to use machine guns against targets instead of HE if the machine gun can do the job. The 75mm weapon gun sight includes range elevations for APCBC, AP and HE, and they are all fired by lining up a target with the gun direction and then elevating the gun to the estimated range. No differences.

The gun sight for 75mm Shermans may have some range elevation markings for smoke. I'll have to check.

If one is firing on a target where armor penetration is needed with HE, the shell delay is set and the round explodes a certain number of seconds after contact.

A 0.05 second delay can be obtained with Sherman 75mm HE, which is good against troops in cover or trenches. Aim in front of the enemy troops, bounce the round off the ground (ricochet fire) and have it explode in the air.

Against anti-tank gun shields and thin vehicle armor delayed detonation of HE works best, cause you don't want the round exploding before it goes through the armor.

Sherman 75mm base emission smoke was an odd round. It was useful from 800 to 1650 yards (I think this is the range, will have to check it tonight), which seems like an unusual range interval. The round was fired by aiming at and hitting the ground in front of a target and having the shell ricochet as it bounced along its path. Smoke was emitted from the base of the round as it bounced along the ground, that's why it's called base emission smoke.

If the round hit the ground too close to the gun, the impact damaged the projectile and it wouldn't work well. 1650 yards was the maximum range due to the low muzzle velocity, poor ballistic shape and max elevation of the gun.

[Howard R]

Thank you. Scanned pages would be very cool!