World War II tank guns

Jonathan Beard's picture

There is a vast literature on the tanks of World War II and their armament. Two things mystify me. For the first half of the war, most British tanks were armed with two-pounder guns. These were 40 mm cannon that fired an armor-piercing shell that was effective against all German tanks at the beginning of the war, and pretty effective even after the Germans improved their tanks and armor in 1942. But in North Africa, British tanks were ambushed time and again, hit by antitank guns, including the famous 88 mm gun. They had no effective reply, because, the books say, “the two-pounder lacked a high-explosive round.” Why was this true? Other 40 mm guns at the time—such as the famous Bofors—fired nothing else. Was there something special about the two-pounder that precluded a HE shell?

In September 1942, just before El Alamein, American-made M-4 Sherman tanks arrived in North Africa. They had a 75 mm medium-velocity gun that fired a very good HE shell. I have read that it contained 1.5 pounds of explosive. It was excellent against soft targets such as antitank gun crews. But by June 1944, when M-4s landed in Normandy, the 75 mm gun’s armor-piercing shells could not penetrate the front armor of the new German Mark 5 Panther. Even the newly introduced 76 mm gun on later model M-4s had trouble with both the Panther and Tiger’s armor, though its AP rounds were considerably better than those fired by the 75 mm gun. I have recently read that many American tank units kept at least a few older Shermans, with their 75 mm guns, in service till the end of the war, because the so-called 76 mm gun (it was actually a 75, too) fired an HE round with only one pound of explosive, much less effective against soft targets.

What was there about the two-pounder that made it impossible to create an HE shell?  Why did the American 76 mm HE round contain less explosive than the 75 mm did?

Jonathan

There is a workable 2009 article on the 2 Pounder Anti-Tank Gun at the following link:

http://www.wwiiequipment.com/index.php?option=com_content&view=article&i...

...that has a table of what ammunition was produced for the "Ordnance QF 2-pounder" and when.

Short form: No H.E. ammunition was produced until 1942 and then in relatively limited quantities (40,000). The next two years sees ten times a much H.E. in 1943 trailing to half that number in 1944 and none in 1945.

It was not the UK Tank corps doctrine to use H.E. ammunition pre-war. Infantry support was what the BESA machine guns were for,

After Dunkirk in 1940, all UK industrial potential for improved 2-pounder ammunition was mortgaged against the immediate crisis replacement of the BEF's equipment set and the fighting in North Africa.

My American lend lease documents say much of that 1943-1944 production of 2-pounder H.E. was lend lease by the USA. Which makes sense because the better metallurgy steel available in the USA meant more high explosive content per shell with better fragmentation than what was available in the UK.

I strongly suspect most of the American lend lease 2-pounder ammunition went to Russia to support the Canadian 2-pounder Valentine tanks on the Eastern Front.

As for the failures of the American 75mm and 76mm versus the German "Big Cats" -- Tiger, Panther, Tiger II -- had to do with intelligence and armor piercing design failures.

The Big cats were death on tracks for Shermans when they were operating in areas of low operational tempo with few avenues of approach and long sight lines. The bocage in Normandy, Italian mountain roads and the French-German border battles in Sep-Oct 1944 all fit that bill.

Until the Normandy fighting Shermans had not faced Panthers in large numbers, with no flanks to turn, where the Panther's gun/armor/optics made a difference. This is when the Isgny France gun tests using service ammunition against captured Panthers showed the weakness of the 76mm service armor piercing ammunition.

In the Normandy break out the Sherman's automotive reliability and much better FM radios allowed them to move farther, faster, in a much more coordinated manner such that Shermans could flank Panthers on a regular basis.

It wasn't until in the Ardennes that the Big Cats could attack on a narrow front the Shermans, whether 75mm or 76mm armed, could not side step that the Big Cats strength in armor and gunpower really told.

The main Sherman problem was the 76mm AP shells were too sharp, too soft and had too big a volume dedicated to a high explosive burster. This was a really bad combination against German high hardness steel armor. US Army 76mm penetrator in a certain velocity range, against 80 to 100 mm steel plate tended to shatter like glass.

The term of art is "Shatter gap failure." It works to look at a kinetic energy penetrator versus armor impact event as an energy budget.

The kinetic energy has to go into structural failure and heat. Where that structural failure and heat ultimately reside is based upon the designed structure and material properties of both the penetrator and the armor.

This was found in 1940 in WW2 with British 2-pounder (40mm) high velocity tank gun shot versus German face hardened tank armor in North Africa and again in the 1944 Normandy campaign when M4 Sherman 76mm APHE shells hit German Tiger and Panther armor.

This was heavily detailed in Lorrin Bird and Robert Livingston's out of print book "WWII Ballistics Armor and Gunnery." This is a 2001 post by Lorrin Bird on the subject of "Shatter gaps."

lorrin Matrix Recruit Member # 3519 posted October 29, 2001 07:36 AM

During WW II, a phenomenon known as shatter gap resulted in hits with too much penetration failing to defeat the armor.

The British noted this oddity in Libya and other North African areas, where rounds that could penetrate beyond 1000 yards would fail at shorter ranges, or hits would fail at short range and then start to penetrate further out.

The theory on shatter gap is that when hits penetrate on half the hits at a given velocity (the basis for most penetration data), there are certain impact forces on the projectile nose. If the velocity is increased and the armor thickness is held constant, the round moves armor out of the way faster, which leads to increased inertial forces on the ammo nose.

If the projectile nose is too soft, such that it absorbs much of the impact energy, the nose can shatter and break up. U.S. and Russian ammunition fell into the shatter gap nose hardness range (less than 59 Rockwell C). While British ammunition was harder than the threshold, some characteristic of the projectiles made it vulnerable to shatter gap.

With regard to Tiger armor, shatter gap normally occurs when the armor thickness is close to, equal to or thicker than the projectile diameter. U.S. 76mm APCBC hits on Tiger armor would fall into this category.

If 76mm APCBC hit the Tiger driver plate at 12° side angle, the resultant resistance would equal 109mm at 0°. With shatter gap, rounds fail when they have 1.05 to 1.25 times the armor resistance, which would result in M10 failures from point blank to 550 meters range, and then penetrate from 550m to 750m.

On M10 hits against the Tiger side armor at 30° side angle, the resistance would equal 103mm at 0°, and M10 hits would be expected to fail from point blank to 800m, and then penetrate from 800m to 1000m.

U.S. Navy tests during WW II against 3" armor at 30°, using 76mm APCBC, resulted in 50% penetration at about 2069 fps impact, and then the hits failed from 2073 fps through 2376 fps.

Firing tests with 75mm APCBC did not appear to result in shatter gap failures, suggesting that impact velocities above 2000 fps would be required for nose failure.

Prior to Normandy, the Americans calculated that their 76mm gun would be sufficient to stop Panthers and Tigers, since the 100mm frontal armor on those panzers could theoretically be penetrated to 1250m by M10's and 76mm armed Shermans. Shatter gap may be responsible, in part, for the sorry showing of those guns in France against heavy German armor.

Regarding the 2-pdr not firing an HE shell, I'm not sure on the technical specifics, but I know that from the doctrinal standpoint British command did not want/think anti-tank units should be wasted on engaging soft targets (at least before 3rd Alamein). They thought that commanders, lower infantry commanders in particular, would be apt to waste them as close-support weapons thereby stripping them of their real purpose. True their Bofors could have offset this somewhat but their conceptual approach to combined-arms normally precluded it from happening effectively.
The lack of an HE shell meant that the anti-tank units had to operate alongside infantry if they were not to be destroyed by enemy HE fire themselves, which then contradicted how higher command expected anti-tank guns to be used and the circle continued....

According to the online Tank Museum "HE was available to the 2-Pounder gun, but British military thinking was that firing Explosive Shells was the job of the Artillery. As such, towed 2-Pounder crews deployed by the Royal Artillery were equipped with HE ammunition, but Tanks, designed for infantry support such as the Matilda II, were not equipped with them."

For more detailed information the 2-pdr HE controversy see https://tanks-encyclopedia.com/ww2/gb/AT-guns/2-pounder.php

There is a good resource that discusses many aspects of armored warfare from the first days to present times, that is Youtube. Fate would have it that I just watched a video between two of my favorite Youtubers Ian from Forgotten Weapons and "the Chieftain" where they discussed your last question specifically: https://www.youtube.com/watch?v=yF4xxYXwLok @ 45:08.

I have watched the vast majority of both of their channel's content, and trust their evaluations, as they never back down from citing legitimate sources for their facts when asked. I think that this is a soft spot in the historical field between the popular historian and the academic historians, as many (myself included) often dismiss social media and popular histories as not being reliable.

Hi

About 2 PDR HE. Australi produced its own version - mainly for use in Staghound Armored cars (post war) and Matilda and Sentinal tanks during the war.

They found that (particularly in the tanks) against Japanese bunker positions they needed a base fused HE round to allow the necessary delay to penetrate the bunker before initiating.

A goood source on the ammunition in Australian hands including illustrations of the ammunition is here => https://www.defence.gov.au/UXO/_Master/docs/Types/Projectile2prRev02.pdf

Cheers
Daniel Ross
Daniel,Ross at Adelaide.on.net