British 75mm MkV tank gun

[kesh]

thanks for that. i'm a fan of the 6 pounder, and the six pounder got the first tiger kills of the western allies, both as an AT gun and tank vs tank.

[Marek_Tucan]

Why there was no APDS shot for 75mm? With some supercharge it might be pretty effective and give 75mm armed tanks somethign to fire at German heavies... Was it because APDS was developped by artillery for antitank guns and armored corps got it just as a by-product?

[kesh]

almost certainly because the barrel and breech wasn't designed for the pressures involved. that was why i was sceptical

the western allies developed similar calibre guns (17 pounder at 76.2mm and M1 76mm) to take high velocity rounds and they were much bigger heavier things.

[cbo]

Marek_Tucan said:
Why there was no APDS shot for 75mm? With some supercharge it might be pretty effective and give 75mm armed tanks somethign to fire at German heavies... Was it because APDS was developped by artillery for antitank guns and armored corps got it just as a by-product?

Dont know why, but it could well have had to do with the somewhat convoluted development history of British tank guns. They had always been high-pressure, high-velocity anti-tank weapons and when they were looking for guns for the next generation of tanks in 1942, it would appear that the weapons of choice were the 17-pdr and Vickers-Armstrongs high velocity 75mm L/50 gun. As the latter turned out to be too big for the Cromwell, something had to be cooked up fast and Vickers-Armstrong could offer a medium velocity 75mm that fired US ammunition and fitted in the 6-pdr mount. I dont think it was ever considered anything but a stop-gap solution until something better was on offer.

As the gun was a temporary measure and fired US ammunition, it might not have been considered worth the effort to spend APDS development time on it, particularily since the Americans were apparently working on the T45 HVAP round anyway.

Add to that the limited advantages you would get from APDS/HVAP in the 75mm gun. APDS would probably not be a much better performer than the experimental US T45 HVAP round, except at longer distances, which wouldn't matter because early APDS was so inaccurate anyway. Of course 117mm penetration is a lot compared with 66mm, but not enough to make a real difference in combat and a far cry from the 208mm of the 17-pdr or even the 157mm of the 76mm US gun.
Add to that the fact that APDS/HVAP was always in short supply, something which would probably have been clear even as APDS/HVAP was developed. Those rounds used strategic materials that was needed for many other purposes and always in short supply, even for the allies.

Then there is the issue of the guns design raised by Kesh. I dont know how much pressure the UK 75mm could handle, but the max. powder pressure of the US 75mm gun was 38,000 PSI, the same as the long US 3" M7 but less than the 43,000 PSI of the 76mm M1A1 tank gun. And a lot less than the always "hot" UK guns, the 2-pdr producing 44,800 PSI, the 6-pdr. 46,000 PSI and the 17-pdr 47,000 PSI.
The M7 and M1A1 fired the same projectiles and achieved the same performance, but the M1A1 did so using a a smaller cartridge with a hotter load, apparently.
The chamber capaciy of the US 75mm was 88 CUI vs 142 CUI of the M1A1 and nowhere near the 300 CUI of the 17-pdr. It was even smaller than the 6-pdr at 100 CUI.

I'm no ballistician, but I'd guess that the combination of a small chamber, shortish barrel and inability to raise pressure to the required levels made it rather pointless to persue APDS/HVAP for the 75mm gun.

Perhaps a similar argument could be made with regards to HEAT. That did not require velocity, but a 75mm HEAT would only raise penetration to 75-90mm, at least if you assume performance on par with German 75mm HEAT rounds. Better than the 66mm of the M61 APC(BC) at 500 yards, but still not significantly so.

cbo

[Marek_Tucan]

Thanks for detailed response!

[DRG]

Good to see you back Claus.

Don

[CharlesM]

I am Charles Markuss, one of the researchers for the ASL system. M72 AP was solid uncapped shot designed for use against homogeneous armour. By the time it was in service with the British in the M3 the Germans were using face-hardened armour against which the M72 often shattered, like the 40mm 2-ponder AP shot. Theoretically the round was APHE but at the time the USA had no suitable fuze for it. The British therefore simply filled the cavity with inert material to boost AP performance, and did so even after a fuze appeared because the first batches at least were very unreliable. M61 was, as stated, APCBC designed for use against face-hardened armour which was still in use on some parts of German tanks, especially the cats. The US army considered developing an APCR round for their 75mm but the performance increase would have been marginal and really a waste of precious tungsten. If they ever seriously considered it (doubtful) I suspect that the British felt the same way about attempting to develop an APDS round for their 75mm as factories were at full capacity producing 6-pounder and 17-pounder APDS. Moreover, as stated already, I doubt whether the guns would have withstood the chamber pressures of more propellant behind the projectile. APDS is of course also hazardous to friendly personnel. The British and US 75mm guns werre really designed for HE and WP.

Incidentally the US army was given 6-pounder APDS for their 57mm gun by Britain but due to the scarcity of targets only about 180 rounds were ever used in Italy, and something over 11,000 in NW Europe.

[chuckfourth]

Hi Charles
I would be verry interested to know which German vehicles had face hardened armour and on which surfaces. I have had some thoughts on the matter myself see.
http://www.shrapnelcommunity.com/thr...b=4&o=&fpart=1
I think that PZ IV turret is face hardened, and the cats side and rear armour was face hardened, also and I believe sdkfz 231 and 232 came in face hardened armor? do you know if this is correct?

[CharlesM]

Leave it with me for a few days.

Regards

[CharlesM]

I've done some checking, and what I said earlier about the cats is not quite right (see below). Face-hardened armour was used on the 4, 6 and 8-wheeled German armoured cars, i.e from SdKfz 221 through to 234 inclusive.

Pzkfw III Ausf G onwards and IV Ausf F1 onwards had face-hardened frontal armour, except for the glacis which was homogeneous, presumably because the slope was so shallow that the extra hardness was not needed, except for the glacis on the Pzkfw IV Ausf D, which had only this plate hardened, but throughout, rather than just face-hardened. PzKfw III Ausf G onwards and IV Ausf F1 onwards had face-hardened upper and lower hull sides, but not turret sides or on any rear armour plates. The last 50% of PzKfw IV Ausf J had only homogeneous plates.

For Panthers it is a bit more complicated, and made worse by the fact that the armour on many Panthers (about 50%) was of poor quality dut to bad heating and quenching processes. Bear in mind that all notionally on PzKfw IV and Panther were often actually 82-85mm thickness. The notional 60mm plates on the Panther nose were usually 65mm, later up to 75mm.

Panther Ausf D had glacis and nose armour face-hardened, aslo upper and lower hull sides. Nowhere else. Panther Ausf A had a face-hardened glacis (poor quality) and a face-hardened nose plate, and face-hardened upper and lower hull sides, but from 9/43 only homogeneous plate was used. From the sdummer of 1944 about half of the Panthers produced had flawed glacis armour. One other reason apart from poor heat treatment may have been the reliance on carbon as a hardener as non-ferrous metals like nickel and chrome dried up. The Panther Ausf G therefore had only homogeneous plate, and again with a glacis plate that often cracked under impact.

Tiger I armour was of better quality, as it was produced earlier in the war, and appears to have always been homogeneous. Tiger II armour was also only homogeneous, but of inferior quality for the reasons already given. Jagdpanther armour was softer that Panther armour, and so less prone to cracking.

Let me know if you want sources.