British 75mm MkV tank gun

[kesh]

read on wikipedia, that an apcbc round was produced for this, with a higher muzzle velocity. spww2 only has ap at penetration 8 for all versions of this gun, as far as i can tell.

Ordnance QF 75mm

sounds fishy to me.

traced this source though, go to page 7

fire and movement

is there any truth in this? i hate that damn gun and it would be nice if cromwells got some decent firepower

[Mobhack]

The values for the UK 75mm were discusses many years ago. It's chief value is as an HE thrower, just like the equivalent Sherman 75mm. Most targets were dealt with by HE, not AP.

UK armoured formations did retain some 6 pdr armed units, because the plain 6 pdr AP was better then the 75mm, and the APDS vastly superior, for the limited times armour needed engaging. In addition 17 pdr specialist tank-killing vehicles were also available. Not to Churchill units - hence the keeping on of some 6pdr armed ones in some formations.

Cheers
Andy

[kesh]

yes i know all that, except the old discussion. i'm curious to know if there's any truth in this second type of ap ammo.

[cbo]

read on wikipedia, that an apcbc round was produced for this, with a higher muzzle velocity. spww2 only has ap at penetration 8 for all versions of this gun, as far as i can tell.

is there any truth in this? i hate that damn gun and it would be nice if cromwells got some decent firepower

I think you are right being sceptical about this "magic bullet" for the British 75mm gun. They had available the range of US 75mm ammunition, meaning the M48 HE round, the M61 APC and the M72 AP (see this one: http://wargaming.info/armour04.htm).

- The M61 was in reality an APCBC round, the Americans didn't record the ballistic cap in the nomenclature for their rounds. The British appears to have used this both with and without its explosive filler. The British were never very keen on explosive fillers in armour piercing rounds and while not having the filler would reduce the destructive effect post-penetration effect, it would avoid problems with premature detonation.
- The M48 came in several different flavours, with three different propellant charges and two different fuzes. It would appear that only the supercharge round was carried in British tanks.
- It seems doubtfull, that the British actually used the M72 uncapped, solid round in combat.

It would appear that they also carried a British made smoke round.

That leaves us with the "magic bullet", an APCBC round with a muzzle velocity of 2,600 ft/s (790 m/s) and penetration of 103mm at 500 yards. The only thing I know of which comes close is the T45 HVAP round, which had a muzzle velocity of 2850 ft/s and penetrated 117mm at 500 yards. But that was an experimental round, never used in combat AFAIK.

Whether there was some sort of "supercharge" APCBC round available is hard to tell from the limited evidence you've found, but it is not something which has found its way into manuals and such, nor is it something I've ever read about in unit histories etc. So if it ever existed, it was not likely fielded.

If you Cromwells run into enemy armour, better use the speed to get away or keep some Challengers or Fireflies nearby - after all, they were included in the TO&E at one per platoon for that exact reason

cbo

[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