Allied Tank Gun Development.

[Enoch]

I was reading through the Appendix of Chamberlain and Ellis that discusses German Tank armament a few days ago. In it they mention that the Germans were able to increase the muzzle velocity, and therefore effectiveness, of several of their tank guns by increasing the caliber length of the barrel.

For instance, the short 75 was increased in length from 24 calibers to 70 over the course of the war. I don't know how much of the increase in muzzle velocity was due to an increase in the length of the barrel and how much was due to other factors. I also don't know to what extent lengthening the barrel requires other changes to a gun.

But, my question is why didn't the American's and British pursue a similar course in developing tank guns. I understand that standardization was a concern and perhaps longer guns would have taken up more space in shipping. Also the 76mm US gun and the British 17lbr solved some of the concerns about the armor penetration of their tank guns. Still, would a longer barrel on the US 75mm or 76mm gun have improved performance?

I'd be interested in what people know and any additional info people could provide on what improvement were made to German guns in addition to the lengthening of the barrels.

Thanks.

[ 09-10-2001: Message edited by: Enoch ]

[Maastrictian]

<BLOCKQUOTE>quote:</font><HR>Originally posted by Enoch:

But, my question is why didn't the American's and British pursue a similar course in developing tank guns. I understand that standardization was a concern and perhaps longer guns would have taken up more space in shipping. Also the 76mm US gun and the British 17lbr solved some of the concerns about the armor penetration of their tank guns. Still, would a longer barrel on the US 76mm gun have improved its performance?

<HR></BLOCKQUOTE>

The grogs will be here momentarily to give you the real answers, but here is what I know.

The 17lber and 76mm can both be thought of as improvement by lengthening the barrel of the 75mm standard Sherman gun.

For various doctrine issues the US designed the Sherman with the short 75mm to be an anti-infantry tank while tank-destroyers took the AT role. When it was realized that tactical realities often forced the Sherman to fight tanks the 75mm was upgraded as much as possible by lengthening the barrel. The barrel really couldn't be lengthened much more as the Sherman's turret was rather small

and a longer gun simply did not fit (note that the firefly (17lber) has a rear counter weight). As I recall, space considerations in oceanic shipping also played a roll in the origional selection of a short (and compact) 75mm gun.

Grog on.

--Chris

[gunnergoz]

I'm not an engineer, but other common-sense considerations in gun upgrades include:

- maximum turret diameter (which impacted recoil length and trunnion placement)

- cartridge case propellant capacity (larger cases for more velocity)

- complete round physical dimensions (impacted stowage, handling and loading)

When the cannon could be upgraded by a simple barrel lengthening, they usually took advantage of this. There were severe limitations as noted prevously, having to do with maintaining gun balance at the trunnions.

For instance, early Grants and the first Sherman prototypes had the short-barreled 75mm gun (they were designed for the longer barrel but none were available at first) and thus required a bulky counterwieght on the end of the barrel in order to balance to gun.

Gun design was a finely-balanced science and there was not too much room for improving a given design once the "system" (breech, chamber, barrel, round) was set. Altering one part of the system basically involved a complete redesign of the other components, making phased improvements less efficient than a complete re-design from the ground-up.

[Lordfluffers]

The 76mm is a completely different gun to the 75mm. It is not simply a longer barrelled version like the German 75mm gun on the MarkIV that replaced the shorter one. Thats why it is called a 76mm gun!!!

It is more probable I think, that the 76mm which was already being developed for the Sherman was considered a much better upgunning proposal than the costs of producing, designing and fitting a lengthened 75mm gun. Im sure some grog will confirm or deny this was the case later.

P.S. the Germans preferred to keep the 75mm calibre because most of their AT and field artillery were also 75mm. ALso when they discovered how obsolete their MkIII 50mm's and MkIV short 75mm's were against T34's and KV's they needed a speedy solution i.e. the long barrelled 75mm.

[offtaskagain]

As already mentioned the German 75mm round also went through some major upgrades through the war. The propellant case on a KwK 42 round is considerably longer than a early war round. Same with Pak 43 to Flak 18/36.

[Dirtweasle]

<BLOCKQUOTE>quote:</font><HR>Originally posted by Lordfluffers:

The 76mm is a completely different gun to the 75mm... ...Thats why it is called a 76mm gun!!!

<HR></BLOCKQUOTE>

Just wondering if that is actually true. Reason I wonder is because a .38 Special has the same diameter as a .357 Magnum round. As the lands in the pistol rifling are .357, and the grooves have a .380 diameter. Hence you can fire a .38 in a .357, but because of strengths in the mechanism / breach, etc. being different you should not ever fire a .357 in a pistol designed for .38.

[MikeyD]

When the 76mm gun was first developed it had a much longer barrel than the production gun (60 caliber lengths maybe?) but with the fancy gyro-stabilized sights the gun needed to balance properly in the turret. I believe a full two feet was lopped-off the end of the gun tube to get it to balance properly!

One Allied gun that did benefit from lengthening was the 6 pounder (57mm). The U.S. gun is notably longer than the original-design Brit gun, possibly done to match the 75mm M3 gun tube's barrel length so they could share the same machinery (my speculation).

[Mattias]

This subject truly is extraordinarily prone misunderstandings

[Redwolf]

You focus on the length too much. The length of the barrel s only part of the higher-velocity issues. More important is that the other components of the gun (the lower part) can withstand the higher pressure that you need for a higher velocity (no matter how you raise the velocity).

As people said, if you improve everything you need to improve to get a reliable higher-velocity gun, you end up with a different beast which usually requires a different mount (stronger, wider).

[MikeyD]

I believe the (modern) Germans just increased the caliber-length of their 120mm NATO-standard gun on the Leopard 2A5 in an effort to maximize the APFSDS dart's velocity. I'm awful at remembering numbers and I'm not near my references but I think it was a jump something on the order of 45 caliber lengths to 60... maybe.

[JonS]

The Brits did upgrade their main AT cannon during the war. Twice in fact, and each tiem by a factor of roughly 3.

2pdr:6pdr early in the war, then 6pdr:17pdr a few years later. I've always thought the consistency of the jumps was kind of interesting, though there is probably a very prosaic reason for it.

Regards

JonS

[Maximus]

Well according to Chamberlain and Ellis, the US 76mm gun had a lower muzzle velocity than the British 17 lbr. It also said that the gun was developed in 1942 when the US realized that the short 75 was not very effective in North Africa. However the 76 wasn't deployed until 1944 due to, I guess, the balancing issue.

[gunnergoz]

The main reason the 76mm gun wasn't deployed on Shermans sooner was the reluctance of the US Army Ground Forces HQ to accept the need for tanks to be adequate tank-killers. AGF was enamored on the tank destroyer concept and felt the 3 inch gun of the M-10 was good enough for killing German tanks. The Sherman was still seen as a weapon for exploiting breakthroughs and supporting infantry. When the tankers themselves clamored for greater parity with the German tanks they opposed the Army finally listened and the upgrade process to 76mm began. The 76mm and the 3 inch were different guns but had fairly similar characteristics.

[lcm1947]

Enoch. I started a post about this very thing back on 8/26/01 titled "American 76mm tank cannon-Why? It has 93 posts to it and will tell you everything you want to know and more. Very good reading I recommend it. Hope this helps?

[Dan Robertson]

I have been studing this for a little while.

Bascially a guns power comes from two properties. The volume of the gun, and the efficency with which it uses this.

There are two basic factors which infulence the efficency of a gun and that is the propllent burn characteristics and the pressure the gun can take. The ideal propellant would burn at a rate which stressed the gun to maxium pressure for all of the time for which the round was in the barrel.

I have found that if you take the gun's "throw weight" (what mass of shot it can throw at a certain speed) and divide by the volume of the gun you get a constant which is similar for all guns.

You can then group gun by their type.

0.32-0.33 (modern smooth bore guns)

0.29-0.32 (British late war to present high pressure rifled guns 17pdr-120mm)

0.27-0.24 (typical WWII AT guns German 88L70 has factor 0.268)

0.19-0.22 (early war or low pressure guns, like Flak 88)

the units are abritary and mearly serve to compare guns with each other.

If we look at two guns that have the same volume, one is short and fat one is long and thin. They fire with propellants which have the same characteristics and the gun barrels take similar pressure)

They guns will both have the same throw weight. However their uses will be very different, the fat gun will require a large shell to fit the barrel. It will project this at a lower velocity. The long thin gun will fire a lighter shell at much higher velocity.

The allied 75mm tank gun was an old weapon it had a low pressure and was also not very long. The 76mm was much longer and also with a higher pressure. The 17pdr was the same size as the 76mm but had a higher pressure and much better propellant.

The German 75 L70 and 75 l48 have very similar factors. But the longer barrel of the L70 allows it to push for longer and thus fire at a higher velocity. To do this it requires a larger cartrige.

[Simon Fox]

<BLOCKQUOTE>quote:</font><HR>One Allied gun that did benefit from lengthening was the 6 pounder (57mm). The U.S. gun is notably longer than the original-design Brit gun, possibly done to match the 75mm M3 gun tube's barrel length so they could share the same machinery (my speculation).<HR></BLOCKQUOTE>I beleive this is incorrect. There were at least 2 marks (actually seems like there were possibly 9+) of the 6pdr, the earlier 57L43 and the later higher velocity 57L50 (not sure when this change occured, possibly Mk3-Mk5?). It seems that there were two US 57mm guns. The first was the 57mm M1 which seems to have a similar performance to earlier 6pdr types and the later 57mm M43 (seen in CMBO) was probably a copy of the later version. My understanding is that the Brit equivalent of the US 75mm gun (75mm QF) was actually a rebored 6pdr.

Interestingly some publications say there was a composite round (HVAP) for the US 57mmM43 which had intermediate performance between APBCHE and APDS. Wonder if it was ever issued?

{edited for additional info)

[ 09-10-2001: Message edited by: Simon Fox ]

[Redwolf]

Am I alone in this opinion, or was the original U.S. plan for TD units with "AT-capable" guns and keeping the normals tanks out of German AFV's way better?

We know it didn't work. However, it occurs to me that it didn't work because too many commanders didn't understand the roles of the TD's, abused the TD's and then naturally the tankers cried for other help. Being let down before, the most desireable help was getting their own AT capability.

What would have happend if TD units had been properly employed and the money spent in upgunning Shermans, new 76mm Shermans and more complicated ammunitions logistics had been invested in more tanks and TDs?

[Andrew H.]

<BLOCKQUOTE>quote:</font><HR>Originally posted by redwolf:

Am I alone in this opinion, or was the original U.S. plan for TD units with "AT-capable" guns and keeping the normals tanks out of German AFV's way better?

We know it didn't work. However, it occurs to me that it didn't work because too many commanders didn't understand the roles of the TD's, abused the TD's and then naturally the tankers cried for other help. Being let down before, the most desireable help was getting their own AT capability.

What would have happend if TD units had been properly employed and the money spent in upgunning Shermans, new 76mm Shermans and more complicated ammunitions logistics had been invested in more tanks and TDs?<HR></BLOCKQUOTE>

Well, the TD concept wasn't as bad as it looks in retrospect. At the beginning of the war, the main combatants all had what could be described as a Tank/TD dichotomy. The German had their 37mm main battle tanks for anti armor purposes, and their PzIV for anti infantry purposes (the Pz IV with the short 75mm gun had less penetration and accuracy than the 37mm). If you were fighting a bunch of infantry, you wanted PzIVs. A bunch of tanks, you wanted Pz IIs and IIIs and 35(t) and 38(t). Of course, the British 2 pounder didn't have a HE shell at all.

And even later in the war, both the Germans and the USSR fielded what could be called TDs with some success.

The biggest problem was not the TDs per se; it was that the existence of TDs was used as an excuse not to upgun the Sherman or make new tanks.

If there were Sherm 76s and M10s in 1943, I don't think that anyone would complain about the existence of TDs.

If Pershings and M-36 Jacksons had come ashore at Normandy, no one would have complained about TDs; even if logistics prevented the Pershings from being produced in large numbers by 6/44, 76mm Sherms plus M-36s would have been fine.

The Germans never complained about their TDs because, as many dumb decisions as German arms designers made, they never did anything like refusing to upgrade the PzIV to the 75mm L/48 on the basis that this gun was already used by the Marder, and the PzIV should be fighting infantry, not tanks.

But some reasons that US tanks were undergunned had nothing to do with TD doctrine. The M-36 probably could have been produced in goodly numbers by June '44; the reason it wasn't was because a lot of people felt like having such a well armed TD wasn't a priority. (It's not clear that this could have been done with the Pershing even if there had been the desire; it was sort of a buggy tank even by the time it was finally introduced, for normal design reasons).

Some commentators have also said that the TD doctrine wouldn't have worked by 6/44 anyway because allied air superiority prevented the Germans from having large masses of armor for the TDs to go and stop. This seems a little simplistic, both because (1) there were many other reasons that could and did prevent panzers from massing; and (2) notwithstanding (1), supra, German armor did mass, on several occasions, to little effect.

[Simon Fox]

Andrew,

Good post. Of course there is nothing inherently wrong with a tank destroyer. All sides used them it's just that most of them saw them realistically as more mobile AT guns (SP guns). It always strikes me as weird when a US publication refers to towed AT guns as "tank destroyers". A designation that could only have been dreamed up by some marketing git who was press ganged for the duration.

Not wanting to detract in anyway but strictly speaking there was a HE round for the 2-pdr. It just wasn't widely issued ("The Gunners" David Horner).

[Kim Beazley MP Ma]

<BLOCKQUOTE>quote:</font><HR>Originally posted by Enoch:

For instance, the short 75 was increased in length from 24 calibers to 70 over the course of the war. I don't know how much of the increase in muzzle velocity was due to an increase in the length of the barrel and how much was due to other factors. I also don't know to what extent lengthening the barrel requires other changes to a gun.

[ 09-10-2001: Message edited by: Enoch ]<HR></BLOCKQUOTE>

Quite a lot. In order to increase the muzzle-velocity you either increase the amount of propellent or allow a longer burning time for the propellent you have. The first can be fulfilled by increasing the chamber size, the second by increasing the length of the barrel.

Eitherway, you will increase the recoil, as more pressure is developed behind the shell in order to throw it out the end of the muzzle faster (remember Newton's little laws?).

With an increase of recoil, you get a need to absorb the recoil so the recoil system must be beefed up. In turn, so must the mounting.

When the Germans increased the barrel length of their 75mm tank gun, they also increased the chamber size. Initially, they over-engineered it. The increase from L/24 to L/43 didn't mean the mounting had to be improved but the recoil system did. Once they increased it from L/43 to L/48, the mounting had to be reinforced and the increase from L/48 to L/70 was made possible. The planned move to an L/100 piece though, required a major upgrade of the recoil system and the mounting, as well as an increase in chamber size - which is why it did not occur before war's end.

The US on the otherhand, decided that it was preferrable to move to a gun which was in the middle of its development cycle, rather than at the end. What must be remembered is that the 75mm M2 gun was a development of the venerable French '75, a design which in 1940 was already over 40 years old. They could have developed it further, as the Germans did with their gun but decided to leapfrog to the 3in, then the 76mm and beyond to the 90mm and 105/120mm guns.

Essentially, one gets the feeling that the US and British were frantically searching for a solution, of being able to put the highest velocity gun available into a tracked vehicle, rather than as the Germans did, which was to stop and say, "hey, there is still a lot of potential in this gun..." and working from there.

[Dogface21]

My girlfriend always says:

" Its not the length of your barrel honey, it how you use it."

Sorry, couldnt resist.

[Mark IV]

German and Russian TDs were designed with the ability to stand and slug it out with tanks... US TDs were not. The doctrine for their employment was for an aggressive commitment in force against massed enemy armor, as FM 18-5 put it:

"Tank destroyer units are employed offensively in large numbers, by rapid maneuver, and by surprise. Offensive action allows the entire strength of a tank destroyer unit to be engaged against the enemy. For individual tank destroyers, offensive action consists of vigorous reconnaissance to locate hostile tanks and movement to advantageous positions from which to attack the enemy by fire. Tank destroyers avoid “slugging matches” with tanks, but compensate for their light armor and difficulty of concealment by exploitation of their mobility and superior observation.

"Rapidity of maneuver enables tank destroyer units to strike at vital objectives, fight on selected terrain, exercise pressure from varied and unexpected directions, and bring massed fire to bear in decisive areas. Tank destroyer units obtain results from rapidity and flexibility of action rather than by building up strongly organized positions. Tank destroyers depend for protection not on armor, but on speed and the use of cover and terrain. When maneuvering in the presence of the enemy they habitually move at the greatest speed permitted by the terrain."

One problem was that conditions for their doctrinal employment almost never occurred in ETO. Commanders who did not understand the TD "theory" but desperately needed fire support, and general dispersal through the theater, were partly to blame, but TDs could not simply be rushed en masse through the choked American road network as a fire brigade most of the time. There were relatively few mass German armor assaults for them to be employed against. The mobility was wasted, when what the crews needed was more armor and more gun... like their German and Soviet TD counterparts.

The open turret and thin armor were negated by the combined arms threat of WWII reality... mortars, artillery, and grenades made all that "superior observation" into a two-edged sword. And when the TDs finally had tank targets to destroy, they had to tiptoe around for flank shots because they couldn't risk a single hit from the enemy.

The German and Soviet designs were built as sloped, turretless, slow, head-on sluggers and those were the TD designs which proved themselves in their intended role: as destroyers of tanks. The American TDs made great contributions to the US effort by virtue of being around with cannons and motors, but only secondarily as destroyers of tanks. They seem to have mostly served as under-armored infantry support tanks and SP artillery, not so much because they were mis-employed, but because they were another answer to a question no one was asking.

[JasonC]

"they never did anything like refusing to upgrade the PzIV"

Hmm. The German quartermasters prevented upgrades of the Pz III from 37mm to 50mm because they wanted to standardize ammunition, and the infantry already had loads of towed 37mm anti-tank guns. When the upgrade was made, the 50L60 was not at first used because the 50L42 was considered adequate, since after all tanks were supposed to exploit, and fight infantry and guns, not armor. Then the move to 75mm long was resisted because so much had been invested in the Panzer III chassis, and it couldn't take a large enough turret to hold the gun. Instead they tried 75L24 in the last model Pz IIIs, while switching the Pz IVs to L48 - hoping to reverse the two roles of GP anti-tank and anti-infantry between the two chassis. They didn't decide to abandon everything with a less than long-75 gun, which meant switching Panzer III chassis production to turretless StuG instead of tanks, until 1943. German tankers had asked for a better gun in the summer of 1940, when they found 37mm couldn't kill British Matildas.

In the meantime, they dealt with enemy heavy armor by use of a PAK front, mobile heavy FLAK batteries, and field artillery firing HEAT ammo. In other words, they used tanks to attack and exploit, and massed towed guns to stop enemy tank attacks. When availble, self-propelled PAK were used to create these defensive fronts more rapidly, to meet threats. These methods were not used by nabobs who didn't understand mobile warfare; they were used by Rommel and company.

The Germans had exactly the same attitudes and problems. They just had them 2-3 years earlier, because they were in action longer and encountered their first tank-killing problems long before the US did. That long after the German tankers first asked for something better than a 37mm, they finally had a Panzer IV with 75L48 that could really do things. That long after US tankers saw action at all, they had Sherman 76s. Bureaucrats and planners and logisticians are always trying to solve their own problems, and only reluctantly realize that their job is to solve "line" tankers and grunts problems, instead. The same is still true today.

One fellow said that there was nothing wrong with the US TD idea except that they were used as an excuse to not field upgunned Shermans sooner. I quite agree. Easy Eights with tungsten would have been plenty, and Hellcats or Jacksons would have worked fine as suppliments to them, in the TD role.

Another fellow said that US TDs didn't kill many German tanks, but if he is talking about the cases when the Germans did attack, this is simply not true. They did very well whenever the Germans had tanks to counterattack with. Panzer Lehr's effort in July in Normandy, and the Mortain attempt, and the Bulge, all saw TDs perform very well in their intended role.

It is true at the time of the force design, the army thought the Germans would be attacking them with armor more often than they actually did. They also thought they'd be attacking them with planes more than they did, which is why there was so much AA too. The force was designed when the Germans were still on the offensive and blitzkrieg was all the rage. Coordinated use of planes and tanks in a rapid, mechanized attack was considered the threat. Independent TD and AA battalions were planned in tremendous numbers to counter these expected hurdles. The numbers of both were progressively reduced as the war went on, because the Germans simply never had the tanks or planes to throw at them.

This is the sort of problem only winners encounter. "Oh dear, I planned all this stuff to beat his attacks on me, and its going to waste because the front is moving monotonically towards his capital at a rapid clip". LOL. (Which is not to say, said lack was -due- to the US. For the planes it was - with British help. For the tanks it was due to the Russians of course).

None of which excuses the boneheaded delay in upgunning the Sherman, or the paucity of tungsten for the 76s they did have. But the idea that this sort of delay and muddle about upgrades to the main battle tank most commonly used, was unique, does not withstand scrutiny. The Panzer III had an equally muddled trajectory. And the German ending point - Pz IVs and StuG III with 75L48, which were by far the most common AFV types in the German force mix from their introduction on - was pretty darn close in capabilities to the Easy Eight Sherman. The US was just several years behind in overcoming such muddles, because it was late to enter.

[Redwolf]

Speaking of open-top allied TDs, shouldn't they have a better rate of fire than a tank with the same gun?

Not neccessarily because of the less cramped gun mount, but they had a gun crew of three men, which mean for me they had two loaders, correct? What's the use if not higher ROF?