75mm T45 HVAP ammunition

This question is provoked by a recent discovery. Apparently the US produced a tungsten-cored HVAP round for the 75mm M3 gun, designated T45. As the designation implies, American ordnance finally elected not to standardize the round. I have seen a few penetration figures quoted (by Nicholas Moran, as I recall) but despite diligent searching I cannot find out anything else online about the T45. Was the round made only in prototype form, or was a larger quantity manufactured? Is there a good source anywhere which would give the T45 story? I've tried on the sister forum but have gotten no nibbles. Thanks to anyone here who knows.

 

I found this, but I can’t confirm “where” the information came from, so I’ll look further to see if I can find the document this may have originated from

 

Thanks. That comes from an article by Moran on his Chieftain's Hatch site which is the most informative thing I've seen so far about the T45. The article is here: The Chieftain's Hatch: HVAP Observations

 

A site with a bit more info or opinions

Sherman Tank Myths - Hyper-Shot (HVAP or APDS) Was Not Feasible For The 75-mm On The Sherman | PDF | Shell (Projectile) | Anti Tank Warfare

 

https://www.theshermantank.com/wp-content/uploads/75mm-M3-spec-booklet-MK-VI.pdf

75MM M3 Gun Information Page | The Sherman Tank Site

 

More interesting than the 75mm HVAP is the fact that there was a 75mm HEAT shell that was already in production and issued with the 75mm M1 Pack Howitzer. IIRC 9 RTR came across a batch of these and fired them from their Churchill 75mm at an abandoned Panther. The results were apparently encouraging but they didn't have time to do a thorough examination before they moved on.

 

Yes, I stumbled across that story years ago and then couldn't remember which unit had done it. It was not the only such experiment with the M66 75mm howitzer HEAT round. As I recall some USMC tankers in the Pacific fired the M66 from their Shermans, but as the case was shorter than the usual ammo for the M3 gun loading and extraction were difficult. The M66 was also tried in the US Army's famous ammo tests at Isigny. I believe on that occasion the warhead was mounted in the standard case for the M3 gun. Is that what 9 RTR did? Anyway, as a result of Isigny the army concluded that the M66 did not offer enough of an improved performance over standard 75mm capped AP to be worth proceeding with. And then of course the Germans developed their own 75mm HEAT for use in the Pak 97/38, which was nothing but the M1897A4 on a Pak 38 carriage. As the M1897A4 was the parent of the M3 I presume that such German ammo would have chambered in the M3. From what I have read the round had pretty good penetration but range and accuracy were not great.

 

The extract from the 9 RTR war diary is below. I got this from a transcription somewhere on the internet, rather than directly from the diary itself.

This has intrigued me for a long time, because it suggested that the Allies may have had a solution to the Panther/Tiger problem all along

 

A special feature of hollow charges is that the terminal ballistic effect decreases with increasing angular momentum.
Therefore, hollow charge ammunition is fired with a low V0, which has corresponding disadvantages in terms of range and precision.
Nevertheless, it is still far better than the best HE ammunition when it comes down to it.

 

The M66 supposedly could penetrate 3.5 inches of vertical homogeneous armor at any range. ("Vertical" and "homogeneous," I said.) The M66 apparently had some value against the Tiger, which had vertical front plates. I have read of 101st Airborne knocking out Tigers with their 75mm howitzers at Bastogne (range not stated). Alas, the July 44 test at Isigny showed that the 75mm M66 would not penetrate the frontal armor of the Panther at 500 yards, which was what the army wanted and was hoping for. This disappointing performance is clearly why the experiment with the M66 was discontinued. So, while the M66 might have helped some against a Tiger and perhaps (?) even against a Panther at VERY close ranges, it was not a wonder weapon. I still would have wanted some if I was in a Sherman. See First Army Anti-Tank Testing against Panther Tank, July 1944

 

The M66 supposedly could penetrate 3.5 inches of vertical homogeneous armor at any range. ("Vertical" and "homogeneous," I said.) The M66 apparently had some value against the Tiger, which had vertical front plates. I have read of 101st Airborne knocking out Tigers with their 75mm howitzers at Bastogne (range not stated). Alas, the July 44 test at Isigny showed that the 75mm M66 would not penetrate the frontal armor of the Panther at 500 yards, which was what the army wanted and was hoping for. This disappointing performance is clearly why the experiment with the M66 was discontinued. So, while the M66 might have helped some against a Tiger and perhaps (?) even against a Panther at VERY close ranges, it was not a wonder weapon. I still would have wanted some if I was in a Sherman. See First Army Anti-Tank Testing against Panther Tank, July 1944

 

Well, 9 RTR's shots didn't penetrate either, so there is some consistency there. What is interesting is that they assert that the Panther would have been knocked out anyway, so presumably something must have occurred inside the vehicle.

 

I was somewhat puzzled by the assumption that a non-penetrating hit would still have disabled the tank:
A shaped charge hardly brings any kinetic energy to the target, which rules out a shock wave, burst armour debris or the like.
It would be interesting to know whether a conclusive explanation was added for this rather curious statement "Complete penetration was not obtained but in all cases the tank would have been knocked out".

 

The most obvious explanation is spalling of the armour plate. Put simply the shock wave from the non penetrating hit travelling through the plate itself is sufficient to blast fragments off the interior side. With those flying around inside the tank, both crew and equipment will get damaged so disabling the tank. The same thing could happen with warship armour.
Spall - Wikipedia


In WW1 tank crews wore metal and / or chain mail face guards to protect themselves from spalling caused by machine gun bullets hitting the outer skin.
http://www.fiddlersgreen.net/vehicles/Renault-FT17/IMAGES/WWI-Tank Operators-German-AV7-Crew.jpg

How much spalling will occur is dependent on the quality of the plate being used in the vehicles. Today there are companies that supply anti-spall coatings and liners to protect against this occurrence.

 

That was my first thought - but a debris cloud is only created after a penetration has taken place.
But the plasma spike has practically no mass that could cause any significant deformation. At least not with a 75mm shell, which leaves the barrel at a maximum of 500m/s. I only know that effect from HESH or large-calibre HE.

For better illustration, the effect of different projectiles on a T-55 turret is shown here:
Shell Impact
The HEAT punctures (No 7) were achieved with a 100mm gun and seem tiny compared to kinetic penetrators.

That's why I'm so curious about how the statement came about. After all, you don't claim something like that if it doesn't correspond to the facts.

 

But it seems that you can get spalling without penetration of the plate simply from the shock wave generated by the explosion passing through the plate itself. See the box top right of the Wiki article I posted. Also a longer explanation in this article when you scroll down it.
https://journals.sagepub.com/doi/full/10.1177/1464420718759704

 

I have been in a tank long enough to have learned a lot about enemy weapons - but I was completely unaware of the destructive effect of a non-penetrating shaped charge inside the vehicle:
If the shaped charge was not in the optimal position to the target, a notch formed in the armour after the explosion without breaking it - in the jargon of the Soviet tank drivers this was called "witch's kiss".
But the tank was definitely not knocked out.

At the moment, I could only imagine a secondary effect caused by bad steel: From about 1942 onwards there was a shortage of alloying elements which made the armour increasingly brittle.
But I would find the original test evaluation more substantial than such speculations.

 

Just a WAG but maybe these tankers (not ordnance specialists) would only call an impact complete penetration if it made a 75mm hole. Maybe the hits made a 20mm plasma penetration? Lt Dan's suggestion that a low velocity HEAT round, about the same mv as a hot pistol round, wouldn't have enough kinetic energy to cause spalling sounds reasonable to me.

 

I would think that after a number of months in the field fighting actual German tanks the guys in 9 RTR would be pretty good judges as to what would knock one out and what wouldn't.

Getting back to the T45...I still have had no luck coming up with a connected story on this round, but there are a few tantalizing hints. It crops up on some wargaming fora since apparently there are games where they let you use just about anything, experimental rounds included. One wargamer who seems reasonably well informed says that T45 rounds remaining after tests were issued to units equipped with the M4A3E2 'Jumbo' assault tank. This guy cites no sources, unfortunately, but a British ordnance collector seems to think the same thing. He also has what he thinks are some actual T45 rounds. Also, some ballistic and aerodynamic info about the T45 is included in a US ordnance guide dating from 1950. This suggests to me that while the T45 was never standardized for service issue or mass produced, more than just a handful were manufactured.

 

I agree. I was trying to say that the HEAT round might have only made a small hole that would have still knocked out the tank, in their opinion.