Cobra

Damn, right in front of my face. That is truly odd though, since I can think of no physical way that would occur, since the only difference is the muzzle brake and rifling twist? Nor have I seen any other reference to it in the Ordnance documentation?

 

I don't see how it explains the simultaneous development of 3" guns in the U.S. and Britain? Development of the 76mm gun for the Medium Tank M4 began in January 1942 and the first two 76mm Guns T1 were completed and tested by 1 August 1942. Development of the 17-pdr as an antitank gun began in April 1941 with the first completed in January 1942. However, development of the 17-pdr as a tank gun was not complete until August 1943. By that time, the development of the 76mm M1 Gun and mounting for the Medium Tank M4 was complete and only awaiting arsenal retooling as part of the "Ultimate M4" program for production to begin at the end of December 1943 and first acceptances in January 1944.

The explanation, such as it is, was that the Americans already had an indigenous gun in the class for both tanks and towed antitank guns...the issue regarding projectile performance was not realized until May 1944 and was never really resolved in the 76mm gun during the war (there was no wartime 90mm AP T33 equivalent for the 76mm gun, instead HVAP was the route followed for improved penetration).

Manic Moran has pretty well covered the Ordnance criticism of the 17-pdr in the Medium Tank M4, which was mainly engineering and ergonomic concerns linked to an attitude of "we already have the same gun, so why reinvent the wheel?" It wasn't really NIH, but misplaced practicality and benign ignorance (the USN tested their own 3" APC projectiles versus Army standard 3"/76mm APC only to find the Army rounds consistently shattered while the Navy ones didn't...because the Navy had learned the lesson of proper hardening in prewar testing, which the Army apparently never asked about).

 

The twist would impact how fast the projectile rotated would it not? That might mean some energy for the faster twist would be in rotational rather than lateral movement. At longer ranges any difference might be a bit more pronounced. Not sure how much difference it could make. Could easily be an error or a statistical anomaly that crept into things. Actually if based on test data I would expect some small differences just to random events.

 

This is an important point. I have read that the US used lower quality steel than the Germans in their AP shells, even if maybe this varied in different shell types. It is interesting however that, according to B. Kavalerchick in The Tanks of Operation Barbarossa American shells were superior to Soviet ones. He mentions Soviet tests at the end of 1944 and writes: The commission that conducted them came to the conclusion that 'the American 76mm armour-piercing shell penetrates the armour of German Tiger H tanks from a range 2-2.5 times greater in comparison with the armour-penetrating capability of the domestic 85mm armour-piercing shells.' (p. 167) This probably reflects problems in Soviet shell design and manufacture procedures.

 

..I thought I read the same thing about poor steel...I thought I was reading about the IS tanks vs the Tigers when I saw it ..but I forget if it was the shells, armor or both....

 

The quality of the steel was little different, if anything American steel benefited from access to alloys the Germans did not have available in quantity. It was the design and implementation of the final tempering that was faulty. The U.S. used simple "sheath tempering" which left a near uniform hardness on the body of the projectile. Given the near universal use of APC design by the U.S., the fuze pocket and HE cavity created weak points where sheer forces on impact tended to fracture, resulting in deformation and/or shattering of the projectile. Add to that the uneven action of the fuze and it created a recipe for multi-point failure.

The Germans used graduated tempering and avoided AP-HE designs, preferring solid shot in larger projectiles. The design insured the shoulders of the projectile supported the very hard point by yielding without shattering, distributing impact stress throughout the projectile. The result was probably the best AP design of the war.

The worst part was that American Ordnance tested and commented on the superiority of the German design on captured Ordnance from North Africa as early as April 1943, but did nothing to implement changes, instead relying on the outcome of its APDS and APCR designs. In the end, American APDS was a failure and APCR had limitations due to range attenuation.

 

Was sheath tempering quicker and simpler? Maybe it was chosen to easy production. Or was US engineering unable to perform graduated tempering?

 

Yes, it was quicker and simpler. Yes, it did ease production. However, it was not that U.S. metallurgical engineers didn't understand how to temper steel, it was that U.S. Army Ordnance considered sheath tempering was good enough...mostly because they literally did not know any better. Navy Ordnance conducted considerable experimentation with the physics of armor penetration and projectile design, thus the resulting "super-heavy" AP projectiles, which packed more penetration into a smaller projectile compared to other designs (the "super-heavy" 16" AP Mk 8 was 2,700 pounds compared to the 2,240-pound Mk 5...and the 1,764-pound German 40.6cm and 38cm APC L4/4).

The problem was the Army, prior to c. 1940 was mostly interested in projectiles going BANG - field artillery HE rounds - rather than armor piercing rounds. Aberdeen Proving Ground did zero experimentation in the dynamics of armor penetration interwar; one of the very few series tested the penetration characteristics of .50 caliber SAP and Ball rounds versus 1/4 and 3/8 inch RHA versus FHA...in 1939. They simply did not have the funding or technical staff to do such studies until well into the war. IIRC, it was 1942 before the labs got the ability to conduct radiographs of armor and projectiles. Worse was the habit of firing American rounds at American targets, which was excellent for telling how American tanks would perform when fired on by American tanks, but no so good for telling how well they would perform versus German tanks and guns. Ditto the reverse, it was 1943 before they began to develop a good understanding of the characteristics of German armor plate.

By 1944, much of the technology was in place, but that only meant that postwar projectile design was considerably better. There though, Ordnance decided to focus on the improving the 90mm gun, rather than the 76mm gun. As late as the Korean War, the main 76mm AP projectile versus heavy tanks was HVAP, with APC as a back-up. While Ordnance did develop an AP round for the 90mm based upon the German graduated hardening techniques and without an explosive cavity, the T33 AP Shot, a comparable round for the 76mm was never developed insofar as I could find.

 

Yes, Kavalerchik in the above quoted book writes about cutting corners to speed production, for instance by partially replacing rivets with welding in some designs in order to speed production, even if at the time Soviet welding techniques weren't as advanced as in some other countries. First KV tanks required to drill 1100 holes for rivets, and then tap thread in 600 of them. This was labor-intensive and time-consuming, so a large amount of rivets were replaced by welding. It seems that a certain lowering of quality standards was consciously accepted in order to increase production.

 

Thanks Rich, you are a "mine" of info! I didn't know Americans were pursuing APDS research too, I supposed that they just borrowed the knowledge from their transatlantic cousins but the design didn't fit their gun models. Do you have some links about it?

It seems tricky to judge shell performance in actual battle from test trials. According to a version of the morning action at Villers Bocage a Firefly hit Wittmann's Tiger on the side from about 200 yards but didn't penetrate. Yet it should have according to the penetration tables.

 

NDRC began research into "hyper-velocity" projectiles in the summer of 1942. HVAPCR (High Velocity Armor Piercing Composite Rigid) was considered so simple that little real effort was put into it, since a functional HVAPDS (High Velocity Armor Piercing Discarding Sabot) would have all the advantages of HVAPCR and non of the disadvantages, so they concentrated research there. The University of New Mexico was contracted to develop a DS projectile for the 75mm gun, 3"/76mm, and 90mm gun, and 75mm and 105mm howitzer (it was the beginning of what is now known as the Energetic Materials Research and Testing Center). Unfortunately, they soon found - like the British - that it was a pretty sticky engineering problem. If the sabot did not separate cleanly, it affected range, penetration, and accuracy. If it separated too soon it did that, plus potentially damaged the muzzle and anyone in the vicinity. Sometimes it didn't separate at all, which resulted in the flight characteristics of a dead pigeon. Work continued, without much success, through September 1944, when it was decided to cancel the research given HVAPCR was proven successful...and much simpler, the 3"/76mm project took about six weeks from initiation to the fielding of the first 1,000 rounds of 76mm for the Isigny test in August 1944.

The British design was only marginally more succesfull, but it took the Canadians postwar to complete an effective design.

Pretty much anything about Wittmann at Villers Bocage that does not stem from the research of a small group of people, principally Michael Kenny or Daniel Taylor, is essentially worthless. It is either hagiographic pap, thinly disguised glorification of the Nazis and SS, pre-digested pap suitable for comic books, or all three. No Firefly hit Wittmann's Tiger from the side, although one reportedly struck the front of it, before it withdrew from the town center and was then knocked out by a 6-pdr AT gun firing from the flank as it attempted to rejoin the main body of Wittmann's company on Point 213.

 

Yes, that's why I added the qualification "a version of..." But it wasn't at long distance engagement, so a 17pdr theoretically should have been able to penetrate the front too.

I've always found Wehraboos irritating. From what I have seen from forums, blogs etc most of those ppl aren't Nazi sympathizers. They seem more like the kids who like the villains from superhero comics bc they are "so cool". Worshiping the German army because you are a far-right sympathizer doesn't make any more sense than worshiping the Soviet army because you are far-left - unless you are German or Russian. And many Wehraboos seem to believe that anything German related to military matters or even to technology - not only from WW2 - is automatically superior to other nations.

 

It reportedly struck the "edge of the driver's visor", which could cover a multitude of sins...especially since AFAIK no photo of it was ever taken.

I did say it was either one of the three or all three. but yes, the typical Wehraboo apparently was emotionally and intellectually stunted about the age of twelve.

 

There is an interesting British statistical analysis (Military Operational Research Report No 33, Tank Battle Analysis) from 1946, which investigates about 200 small scale engagements involving Western and German tanks, SP and towed AT guns from the Tunisian campaign to 1945. With few exceptions the engagements involved no more than 15 vehicles on each side. It gives interesting conclusions, some not unexpected: for instance in most engagements the side who fired first was successful, and SP/TD were much more successful than towed AT guns, especially for the Allied side.
They also calculate effectiveness values (without considering stance or terrain however) and conclude that German tanks were about 30% more effective than Allied tanks, i.e. Allied tanks needed about 30% numerical superiority to have the same chances of success as their opponents. German tanks on average were successful at longer ranges than Allied tanks, while the opposite was true between German and Allied SP/towed AT guns.
The study also breaks down the engagements according to different types of vehicles used. A surprising result are the engagements between Sherman and Cromwell tanks (both armed with 75 mm) against Panthers and Tigers. Of 17 engagements, totaling 37 Allied and 24 German tanks, the former won 12 and lost 9 vehicles, while the Germans won 5 and lost 15 tanks. The Allied were the attackers in 14 cases, the Germans in 2 while in one case the stance is unknown. One caveat is that probably at least some of the German machines were misidentified and were in reality PzKpfw IV with long 75. I think also that 17 actions are too few to allow strong conclusions. The analysis also don't consider eventual factors that could have influenced the engagements, like artillery support (even if in most of the actions analyzed there was no infantry support present).