Small tank guns?

[BlairWitch749]

the main limits where weight on all other materials

big guns require big turrets which are heavy, which in turns puts additional demand on suspension and other key components

tank engine design lagged aircraft engine design significantly throughout the 30's, and it just wasn't feasible to produce things over 25 tonnes and have any sort of reasonable power to weight ratio

that's part of the reason the t-34 was so revolutionary... not just the cannon and the thickish (for the period) armor, but it had the power in it's engine to go on road and cross country at medium speed; it was a combination of speed,armor and firepower a full generation beyond any tank on earth in 1941

 

[Wet Coast]

A third, very British, problem was the mental divide between "cruiser tanks" and "infantery tanks" with totally different roles and weapons.

As mentioned this wasn't really just a British problem. The US divided the two concepts into tanks and tank destroyers where tanks were expected to be the "infantry" vehicles and not fight other tanks.

 

[TyranicusMaximus]

Of course, although the implementation was far from perfect, and they were a tiny minority of the tanks fielded at the start of the war, but the Soviets had the right idea with the 76mm gun fielded by the T-34 and the KV-1.

 

[iddt3]

You had two types of tank guns. Anti-tank guns which had to have a lot of kinetic power to punch through enemy armor, this were the small calibre guns, long barrel giving them enough energy to do what was required of them. Then you had anti-infantry guns which had to be big so they could pack a lot of explosives and could do serious damage, those were large calibre guns. So you had two guns and two types of tanks. Pz III was anti-tank, Pz IV was anti-infantry.

It wasn't until later (1943ish) that you get guns that could do both, have large calibre for AI rounds and create enough energy for AT guns to be effective, thus creating a new class of main battle tank which could do both jobs. Multi gun tanks, AI and AT, were mostly failures.

It's worth noting that US resisted Sherman Firefly upgrades because they thought it will only marginally improve their AI capability, which was seen as main task for their tanks, tanks would be handled by SP AT guns.

And it's also worth noting that IS series of Soviet tanks were designed with AI in mind, though the sheer ammount of explosives in round could knock out most German tanks even if round sucked at AI.

The 76mm cannon on the firefly actually represented a mild decrease in explosive power, due to the increased thickness of the rounds casing.

 

[aktarian]

The 76mm cannon on the firefly actually represented a mild decrease in explosive power, due to the increased thickness of the rounds casing.

More reason for to stick to their Shermans as they considered them to be used against soft targets.

 

[bsmart111]

I don't think we can say that was a uniquely British idea. As mentioned earlier in the thread, the Panzer III and Panzer IV were another example of that sort of thinking - consider the differences in armament there.
A good example of a similar philosophy is the Grant - a 75mm gun in the hull for infantry support, and a 37mm AT weapon in the top turret. That's combined in the same vehicle, of course, but there weren't many truly multi-purpose weapons early in the war.

The Lee/Grant was not a philosophy driven design but a production one. The U.S. Army wanted a 75mm gun armed tank but there was not enough production machining capability to produce turret rings large enough in volume to support tank production. So as an interim design the 75mm was mounted in the hull and the 37mm (which required a smaller turret ring) was put in the turret. As enough machining capacity became available the Sherman was put in production with a minimum of production disruption (The Lee/Grant and the early Sherman has a very high level of commonality from the tracks down) I have seen a picture of a tank factory where there are Lees in the foreground and when you look very closely you can see Shermans following them down the production line with less disruption than a normal 'model year' change would require.

 

[bsmart111]

The 76mm cannon on the firefly actually represented a mild decrease in explosive power, due to the increased thickness of the rounds casing.

The 17pdr represented a MAJOR decrease in HE capability. I used to have a chart showing HE capability of various rounds. of guns used on the Sherman chassis the 75mm & 90mm were almost equal, the 3" and 76mm were about 15-20% behind and the 17pdr was something like 40% behind if they could get HE rounds for it. the British did not plan to use HE rounds in AT guns. In fact they did not use an HE filler in any AT rounds. Most were solid shot (both capped and uncapped) American and German AP rounds of 75mm and larger used an HE filler to enhance the damage when it penetrated. The British had American made rounds for their 75mm armed tanks but insisted that the rounds be delivered without the HE filler

 

[MattII]

More reason for to stick to their Shermans as they considered them to be used against soft targets.

However, the 75mm guns are pathetic front-on against Panthers, while the 17pdrs were real killers. The British solved the problem by bracketing a single Firefly with 3-4 normal Shermans. This didn't end up complicating the supply trains much since the 17pdrs were in pretty widespread use by that time.

 

[aktarian]

However, the 75mm guns are pathetic front-on against Panthers, while the 17pdrs were real killers. The British solved the problem by bracketing a single Firefly with 3-4 normal Shermans. This didn't end up complicating the supply trains much since the 17pdrs were in pretty widespread use by that time.

Yes, but as I said earlier, US expected tanks to fight soft targets and TDs to fight tanks so increase in Sherman AT capability was seen as nice but not something that was neccesary or even desired. Plus US never made that calculation "If Germans had Pz IIIs and IVs in 1939, had long barrelled IVs in 1942 and few Panthers in 1943 they'll get heavier tanks and more of them in 1944."

US was in different position regarding logistics so anything that would interfere with it (and adding another gun to arsenal wold) had not only had to be nice but neccesary.

Fireflys in US service had everthing working against them.

 

[Riain]

The US found out that HE content wasn`t as important as armour penetration, tanks needed to slug it out with other tanks. Hence the E8 with the 76mm gun which was a reversal from prewar doctrine.

 

[aktarian]

The US found out that HE content wasn`t as important as armour penetration, tanks needed to slug it out with other tanks. Hence the E8 with the 76mm gun which was a reversal from prewar doctrine.

But not before Normandy.

 

[Riain]

The US wasn`t particularly heavily engaged in armoured operations before Normandy, whereas the British had been fighting in the desert since early 1941 and were upgunning their tanks soon after.

 

[aktarian]

The US wasn`t particularly heavily engaged in armoured operations before Normandy, whereas the British had been fighting in the desert since early 1941 and were upgunning their tanks soon after.

True, but it's not as if Brits were hiding this stuff from Americans.

 

[Sior]

True, but it's not as if Brits were hiding this stuff from Americans.

There's none so blind as don't want to see!
If Britain was beset with Col Blimps at the start of WW2, America had General Blimps the evidence disproved their theories so they just ignored it and hoped it would go away.

 

[wietze]

But not before Normandy.

or to be more precise, only after the main obstacle for progress for the US armored forced was kindly removed by the the US Airforce (= killing gen lesley Mcnair with a direct hit). McNair was the major obstacle for changes from the doctrine, and it was him who blocked all attemps at developing a heavy tank. Only after mcnair perished they were able to pick up develop of heavier tanks.

 

[Slowpoke]

Another reason for the small guns was tank size itself.

Interwar tanks were quite diminutive compared to late designs. As technology progressed, larger, more powerful engines were developed, able to push the extra tonnage.

 

[NothingNow]

Another reason for the small guns was tank size itself.

Interwar tanks were quite diminutive compared to late designs. As technology progressed, larger, more powerful engines were developed, able to push the extra tonnage.

Well, the engines were there, as were the guns, it's just that no-one besides the Russians and French really gave a fuck about anything larger than 8 tonnes right up till the mid 30's (baring half-hearted british experiments with the Medium MkI-III,) and the French didn't see a role for Medium/Heavy tanks that required much in the way of speed, so a Medium or Heavy tank putting out less than 10hp/tonne was just fine, and the engines were optimized for torque over horsepower (which is actually very nice for everything except aircraft.)
Which considering that everybody also wanted to keep things cheap, meant that light armor was also the order of the day, thus a fairly small gun could do the job required of it.

All leading in to the odd period where Japanese Medium tanks were actually very competitive, especially the Type 97 Chi-Ha (with a passable power to weight ratio, effective gun, and less dangerous diesel fuel,) right up until it met the all around superior BT-7.

Now, if anyone had actually run the numbers, and decided to develop their own tank for defensive use in the period, especially while reading JFC Fuller and Stavka publications (especially those by Triandafillov and Tukhachevsky regarding Deep Battle) they likely would've built something like a value engineered Panzer IV Ausf. F with a french 75 as the main gun (cheap, plentiful, and very, very effective. )

Incidentally, regarding armor and all that, does anyone have information on Loading gauges for Spain, Portugal and Latin America? It's for my Latin Pact thing.

 

[Riain]

I`ve often wondered about early war tank engines, if good ones could have been designed instead of just finding an existing truck engine or a libery aircraft engine.

 

[NothingNow]

I`ve often wondered about early war tank engines, if good ones could have been designed instead of just finding an existing truck engine or a libery aircraft engine.

So, like the Soviet Diesel model V-2? Which was used in pretty much every Russian AFV produced from the introduction of the BT-7M until the introduction of the T-54. And displaced something like 38-39L and put out between 450-700hp in a very nice V12 engine, which is a very virtuous layout, (given it's inherently perfect balance, relative simplicity, high reliability, low idling speed and longer engine life.)

That's pretty much the answer right there (although fitting it with spark plugs incase you need to run petrol through it might be nice) and it might need to be shrunken down a bit depending on the vehicle, but a displacement under 12L seems like it'd be too small for an AFV, and a truck could get by with a 6-9L straight 6 derivative, which would allow a pretty extreme level of parts commonality, since everything short of the crankshaft and belts and several parts not likely to be replaced in the field would be shared, and you wouldn't have to train the mechanics on so many different engines.

 

[Riain]

I thought that as well, but of course that lack of cash is the major obstacle which is why the Brits used such shitty engines in the first place.

What about the drivetrain? As discussed earlier the width of a tank is set by the loading gauge of the railways, 2.85 metres in the British case, 3.1m for Germany and 3.35 for the Soviets. Tanks must also be within certain length/width parameters, so you can`t have a narrow but very long tank. British and Soviet tanks had their drive sproket at the back, whereas German and US tanks had it at the front. I tend to think a front drive sproket makes for a more compact tank which is what the pre-war planners wanted, but that`s just my non-engineer opinion.