Saturday, 6 August 2016

17-Pounder: Britain's Long Arm

The development of anti-tank artillery followed more or less the same process in many countries. This resulted in the USSR creating a 100 mm BS-3 gun in 1944 and the Germans with the 88 mm Pak 43 gun, a weapon with excellent characteristics that forced Soviet tank designers to rethink their requirements for armour protection. However, the British arrived at the best solution, creating the Ordnance Quick-Firing 17-pounder, which had the most balanced characteristics. You can familiarize yourself with the gun in detail by viewing these photos and read about its creation and trials in the Soviet Union here.

With Room to Spare

The fact that the 40 mm 2-pounder gun, adopted in 1935, wouldn't last long on the battlefield was obvious by 1938. The arsenal at Woolwich (ROF Woolwich) began developing a new gun with a caliber of 57 mm. The first barrels for the Ordnance QF 6-pounder were ready in 1940, but the development of the gun dragged on until the year later, and mass production only started in 1942. This delay (both for the tank and anti-tank versions) led to these guns only being used in the battle for El-Alamein that same year.

Meanwhile, in 1941, before the trials of the Ordnance QF 6-pounder, an idea was raised that the new gun won't last long on the battlefield either. To be fair, the 6-pounder turned out to be a great gun, with the 50 caliber version having similar penetration characteristics to the Soviet ZiS-2. Nevertheless, the idea of beginning work on a replacement for the 6-pounder was approved. The Ordnance Committee also learned that the Germans were working on a 75 mm gun capable of penetrating 80 mm of armour at 1800 meters. This was the Pak 40, which appeared on the front line in the spring of 1942 and compensated for the thicker armour of Soviet tanks.

17/25-pdr in Africa, winter-spring of 1943.

On May 15th, 1941, the Ordnance Committee began work on the new anti-tank gun. According to the requirements, the gun had to penetrate 120-150 mm of armour at 730 meters. The 3 inch caliber (76.2 mm) was chosen. This caliber  has been in use by a British AA gun developed in 1914, but the 17-pounder had no connection to that gun.

The mass of the shell was 17 pounds (7.7 kg), which gave the gun its name. The muzzle velocity was set at 823 m/s, more than the AA gun. The final figure was even greater: 908 m/s for the AP shell and 1200 m/s for subcaliber ammunition. This high muzzle velocity was attained with a 55 caliber barrel and a very large casing.

OQF 17-pdr Mk.I, the most numerous variant, at the Gorohovets proving grounds.

Two experimental OQF 17-pdr guns were ready by September of 1942. Two versions of the gun were submitted for trials. The first, Mk.I, was a towed gun. The second, Mk.II, was designed as a tank gun. Both guns showed themselves well during trials, but there one small problem. There were no plans to begin production for a mount until 1943. Meanwhile, the Germans were unwilling to wait. On November 20th, 1942, Tiger tanks from the 501st Heavy Tank Battalion were sent to Tunisia.

Same gun, from the front.

The solution to the mount was simple. The first 100 17-pdr anti-tank guns were put on mounts from 25-pdr guns. This hybrid, dubbed 17/25-pdr gun, made its debut in February of 1943. To maintain secrecy, they were codenamed "Pheasant". The main modification, 17-pdr Mk.I, entered full production in 1943. The new mount lowered its height to 1600 mm, which is very low for such a powerful weapon. To compare, the BS-3 was 1800 mm tall, and the Pak 43 was 2 meters tall.

Trying Out New Toys

Unlike the 2-pdr and 6-pdr, supplied by Britain to the USSR, the Red Army did not use 17-pdr guns. Nevertheless, at least two guns with serial numbers #1926 and #5593 were tried at the Gorohovets proving grounds in Mulino. According to correspondence, GAU first found out about the guns in early 1944. By February 14th, a trials program was composed and sent to the proving grounds. Gun #1926 arrived on April 6th, 1944.

Its trials had to be postponed until the fall. The gun arrived not only without a limber, but without any shells, 254 of which arrived on August 31st. In addition, it seems that no sight was provided with the gun, as only one sight is listed (#5515) and it arrived with gun #5593 in October. As a result, trials began on September 8th and concluded on November 10th. 136 shots were made during that time, 15 of them with an increased propellant load. The gun was also towed for 40 kilometers during trials.

The gun is showings its maximum gun depression.

Trials achieved a muzzle velocity that we would expect, 908.7 m/s. Interestingly enough, the British manual was translated incorrectly, and the muzzle velocity was listed as 3000 fps (914.4 m/s). Based on this fact, the conclusion that the data in the manual is incorrect was made. The original manual published in 1943 lists the muzzle velocity as 2980 fps (908.3 m/s). The shells with increased propellant had a muzzle velocity of 930 m/s. It's worth noting that the gun only arrived with regular armour piercing ammunition, while the British were already using subcaliber ammunition with higher penetration.

Rear view, trails deployed.

Precision trials were made at a range of 1000 m. Trials showed that the British gun had superior precision to the Soviet 76 mm AA gun mod. 1938. A rate of fire of 8 RPM was achieved during trials. Only 3 shots from the fired 7 hit the target, but the mechanical accuracy was not the issue. Since the gun arrived without a sight, an attempt was made to equip it with an optical sight from a 2-pdr gun. That sight malfunctioned, and the trial had to be done using backup iron sights, which were not suitable at a range of one kilometer.

The trial record admits that the testers were untrained and that the real rate of fire could be as high as 8-10 RPM. When shooting at a moving target, 4 shots out of 5 hit at 500 meters. At 1000 m, 2 shots hit.

17-pdr gun in travel position, attached to a Studebaker US6 truck.

No trials of maximum penetration were made. Penetration was only tested against multiple plates positioned at a straight angle and at 30 degrees. A 100 mm thick plate could be penetrated from 1800 meters when flat, and from a kilometer when angled. A 90 mm thick plate could be penetrated from 2 kilometers, or from 1200 meters at 30 degrees. A 76 mm thick plate could be penetrated from 2200 m. This was higher than the 85 mm S-53 gun, and about the same as the BS-3 with BR-412 ammunition. The German 8.8 cm Pak 43/41 had better penetration, but it was much larger and almost twice as heavy.

During trials, the automatic mechanisms worked flawlessly. The ability to regulate the recoil length using special markings on the front cover of the mount was commended. It turned out that the indicator was positioned inconveniently and could be covered up by the gun shield, the design of which was also judged to be good. The spaced armour design reliably protected the crew from rifle caliber bullets.

The gunner's station. The flywheel handles were made from metal, which caused discomfort in the winter.

However, the 17-pdr gun had its drawbacks. The effort to fire the gun was as high as 20-30 kg, which was very high. The effort to open the breech was as high as 15-20 kg, also high. The testers also did not like the fact that the flywheel handles were made from metal, which resulted in discomfort when using them in the cold. The work of the trigger mechanism was also found unsatisfactory, as the levers snagged on each other and impacted when the gun was brought back from recoil. A sizeable drawback was the presence of a muzzle brake. After firing, it kicked up a cloud of dust, made the crew's job more difficult, and revealed the position of the gun. However, muzzle brakes were installed on most medium and heavy AT guns, so this problem was common.

Low Mobility

The trials didn't end there. No matter how well a gun can shoot, other characteristics are important as well. Unlike heavier artillery, anti-tank guns fire directly at their target, and have to be moved often.

The gun shield, composed of two 6 mm thick plates.

An issue arose even before this procedure. Gun #1926 arrived with a dent on the inner side of the left trail. The dent was relatively small (30 cm long, 5-7 mm deep), but after 20 shots the trail started to deform and a crack appeared. After firing trials, the trail was so deformed that it could no longer lock in travel position. Deformation of the spades was also recorded. The right trail did not deform, so this was most likely a manufacturing defect, but this incident was recorded as proof of an insufficiently robust mount.

If the problems with the mount were unclear, then another problem was quite obvious. The mass of the OQF 17-pdr Mk.I was 2862 kg, and the crew consisted of only 7 men. It's worth mentioning that the Soviet BS-3 weighs 3650 kg with a crew of 6. The author's personal experience in pushing the gun along even asphalt suggests that 7-8 people are ideal for this task, one of which hangs off the barrel as a counterweight. However, the Germans managed to outdo everyone, with their 4.5 ton Pak 43 and an 8 man crew. It's nearly impossible to push around such a heavy gun on the battlefield, and it's no wonder that these guns were frequently left behind due to a lack of things that could tow them away.

Gun shield from the back.

It took between 40 seconds and one minute to bring the British gun into fighting position, and about the same amount of time to bring it back to the travel position. It took 10-13 second to turn it 90 degrees, and 30-40 seconds to turn it 180 degrees. The biggest trial was pushing the gun over a field covered in 20-30 cm of snow. The gun was pushed barrel forward with joined trails. It took almost 3 minutes to travel 100 meters.

Muzzle brake.

It can't be said that this torment of the gun was an attempt to discredit the British gun. These situations happened very often at the front, and not only on the Eastern front. If the Allies didn't have to push guns through snow as often, mud was still a common occurrence. The verdict of the Gorohovets testing crew seems fair when you consider this fact.

"It is impossible to transport the gun over 500 meters off-road with only the crew's strength. The 7 man crew can push the gun over only 100 meters on even terrain. Transport by hand is also difficult due to a lack of comfortable handles.
...
The penetration, stability, and precision of the 17-pdr gun made it a powerful anti-tank gun that matches modern requirements.
However, the weight for this caliber is high (2862 kg), the coefficient of metal use is low (112), and there are many other drawbacks, noted in section 3 of these conclusions."

It's difficult to consider these conclusions sensational or unfair to the 17-pdr. The issue of excess weight was not sudden, and the Germans were the first to encounter it, not the British. The Pak 40 which inspired to British to make their own powerful AT gun could only be moved across the battlefield with great difficulty. This was one of the few reasons for the development of self propelled gun mounts on light tank chassis. The aforementioned towed Pak 43 made its debut alongside vehicles which carried the same weapon.

Deformed trail after firing trials.

The British were perfectly aware of the fact that the gun was too heavy to push around the battlefield. The simultaneous development of the tank and towed versions of the gun was no accident. Of the seven modifications of the Ordnance Quick-Firing 17-pounder, five were for tanks or tank destroyers. This highlights the fact that the British tried to compensate for the weight of the gun with a self propelled chassis. However, the towed version persevered, as it was still much easier and cheaper than a tank destroyer. Its mass, penetration, and size put the British gun above its foreign analogues, and these are much more important factors than the speed at which its crew could push it around.

5 comments:

  1. Was this thing unwieldy unside the Firefly, has the Chieftain said it was?

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  2. This was higher than the 85 mm S-53 gun, and about the same as the BS-3 with BR-412 ammunition.

    The WWII Gun vs Armor Calculator has the APCBC round of of 17-pounder penetrating 177 mm of armor at near point-blank range, inferior not only to the German 88 mm/L71 as this article cites, but also the Russian 100 mm D-10 and the Russian 122 mm A-19 by considerable margins (about 30 mm or more), and marginally inferior to the German 75 mm/L70 (about 15 mm).

    I assume the article is citing the standard APCBC round because the APDS round's penetration is slightly superior to the German 88 mm/71.

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    Replies
    1. Yes, the Soviets never received APDS ammunition to test with.

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    2. WW2 Gun vs Armour calculators does not reflect reality well because it presumes ideal projectile quality (unbreakable). The reality shows a large span of variation in contemporary projectile qualities, and their respective sensitivity to break up at various velocities and obliquities.
      Performancewise, and using AP ammunition, the 17pdr is about the equal of the 75mmL70 KWK42 / PAK42.
      However, the penetration performance at high striking velocities did require also a demand for highly alloyed steel, capped AP-shot projectiles, to prevent projectile break up striking at low or moderate obliquities.
      This was not an option for the Soviets during ww2, consequently, this whole system was not going to be adopted, ever.
      With domestic, low grade and uncapped AP ammunition, the performance would be the same at high obliquities, where projectile break up occurs nevertheless but decidedly inferior at low obliquities and ranges where the velocity is high enough for break up (presumably, down to levels approaching the 0° short range performance of the 75mm PAK 40 because complete projectile break up causes a roughly 1/3 reduction in penetration at 0°).

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    3. WW2 Gun vs Armour calculators does not reflect reality well because it presumes ideal projectile quality (unbreakable).

      That is simply untrue. If you look at the predictions based on their site, they *do* predict likely failure due to round shattering, especially at oblique angles, and especially for uncapped AP rounds. Capped rounds perform better, as you say. But even allowing that, the BS-3 and D-25T Soviet guns are still more potent than the German 75 Kwk42/L70, which in turn is marginally better than the 17-pounder. If you take a Sherman Jumbo hull as the target (chosen because it's a reasonably tough target but not impossible target for all these guns, so that you can see the differences) the frontal penetration for the BS-3 is 900 m (uncapped AP round), for the D-25T 800 m (uncapped AP round), for the German 75 mm Kwk42/L70 600 m, and the 17-pounder 500 m. That's almost a 2-1 difference between the BS-3 and the 17-pounder range-wise for penetrating the same armor plate. And mind you, that's comparing uncapped Soviet rounds versus the capped German and British; use the Soviet capped rounds for both guns, and the difference is huge.

      I have quibbles with the WW2 gun versus armor calculator site too--but that's because it appears too reliant on German sources. Take the Panther's frontal hull--with it, the calculator predicts that all these rounds (BS-3's uncapped, D-25T's uncapped, and German 75/L70's and British 17-pounder's capped) all will bounce, even at point-blank range. But that's not the experience of Soviet tankers, who reported that their uncapped BR-471 122 mm *COULD* penetrate the Panther's frontal hull at ranges closer than 700 m (the turret could be penetrated much farther away). Here it wasn't the thickness of the Panther's hull armor that was the problem, but the hull's slope (after all, the Tiger I's thicker armor could be penetrated up to 2k) and the fact that the pointed BR-471 round had a hard time with sloped armor.

      This concerned Soviet designers, who labored to either put a BS-3 on the IS-2 or to upgrade the BR-471 round. Finally, Soviet designers decided on taking the latter tack with the BR-471B, which solved the problem. Before that solution was implemented, the Geramns' lack of good alloys even before then "solved" IS-2 crew's problems when the D-25T's uncapped round suddenly started penetrating now-brittle Panther hulls even at 2500 m.

      So who do you believe regarding the performance of the BR-471 versus the Panther's hull? I believe the reports of Soviet tankers, if for no other reason because of the overmatching effects of a large, massive, round like the BR-471 hitting armor considerably thinner than the thickness of the round. You can only get so much protection from sloping armor; actual thickness counts too.

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