75mm T45 HVAP ammunition

source: https://apps.dtic.mil/sti/pdfs/AD0800469.pdf pg.64 + some scarce statistics/numbers in the following listings

 

Well 9 RTR did state that "Complete penetration was not obtained", which perhaps suggests that an incomplete one was.

 

Interesting explanation why T45 was not adopted:

(...)
75mm HVAP T45 Shot (APCR-T)
Cartridge Weight -13.50lb
Projectile Weight - 8.4lb
Velocity when Fired from 75mm Gun M3 and M6 - 2,850fps (869mps)
Maximum Powder Chamber Pressure 38,000psi

Muzzle Energy (my calculation) - 1,441,827 joules

Penetration of Homogeneous Armor at 30 degrees obliquity
4.6in (117mm) @ 500 yards
3.8in (97mm) @ 1000 yards
3.1in (79mm) @ 1,500 yards
2.5in (64mm) @ 2,000 yards

We can see real easy now why this tungsten was not adapted. It does make the 75mm Sherman capable of defeating a Tiger at 1,000 yards, but this is not functionally better then the performance of the 3in gun firing steel ammo. In fact at 1,500 yards the 3in gun is already superior due to the heavier shell weight keeping up velocity. (...)

SOURCE: WW2 Tank-Anti Tank Gun Muzzle Energies - StarDestroyer.Net BBS

 

For the sake of completeness, something about the M66
SOURCE:
https://ia902601.us.archive.org/22/items/Tm9-1901/Tm9-1901.pdf
pg. 125

 

Yes, I saw that post. That is the same fellow who reported that T45 rounds remaining after tests were allotted to units with the Jumbo. But he cites no sources for that assertion.

 

The data on the projectile itself correspond to those of the source I posted in post #21 (pg. 70-72).
I have not checked the data on the penetration performance.
Nevertheless, I found the approach convincing: tungsten is a rather demanding material.
If special rounds do not achieve significantly better values than an ordinary steel slug, then this does not justify the production effort.

 

That post compares 75mm HVAP against 3" AP though, the 3" gun (as fitted to the M10) being quite a bit more powerful IIRC.

So I'm not convinced of his reasoning for the 75mm T45's rejection, as the 3" gun was pretty much obsolescent by this time. Am I correct in thinking that the US Army was turning wholesale to 76mm armed Shermans by this time? That would seem a more rational explanation.

 

Well, both explanations boil down to the same thing: it wasn't worth the effort
In any case, the shadowy existence of the T45 explains itself

 

Thoughts turned to development of a 76mm armed tank in late 1942. Initially with Sherman but the original turret was deemed too small. Then during 1943 with the T20 series of tanks culminating in the T23 with a larger turret. Then in late 1943 the decision was taken to put the turret from the T23 onto the updated Sherman hull. The first 76mm armed Shermans began rolling off the production lines in Jan 1944.

But there was still a demand for 75mm Shermans which led to production of the M4A3(75)w continuing until March 1945 (over 3,000 of that model produced from Feb 1944) along with remanufacturing programmes for earlier 75mm Stateside training tanks.

On the tank destroyer front, the last 3” armed M10/M10A1 rolled off the production line in Dec 1943. Production of the 76mm armed M18 had begun in July 1943 with 90mm M36 production beginning in April 1944.

 

I wonder why. I thought Jumbos weren't used a lot against other tanks.

 

254 M4A3E2 Jumbo produced May-July 1944

On 31 Jan 1945 Eisenhower was looking for as many more Jumbos as he could get without disrupting the overall flow of tanks to the Continent. But he specified that they should have 76mm guns. In the short term a programme was begun to upgun existing Jumbos. Eventually about 100 were converted starting Feb 1945. They were photographed in action on from about 6 March 1945.

 

Some images of the round in question:
1. A disassembled T45 warhead, evidently copied from an official publication of some kind.
2. A purported T45 round in the possession of a British collector.

 

Though Jumbos were intended for the assault role rather than anti-armor, the fact that they were considered important enough to warrant re-arming with the 76mm gun is interesting and possibly relevant to the T45 story. SHAEF clearly wanted Jumbos to have as much hitting power as possible, so the allocation of T45 ammo to 75mm Jumbos would have been in line with this policy.

 

My understanding of the Jumbo is that it was mainly used as a point vehicle for armoured columns (i.e. it was the tank likely to be shot at first).

From what I recall its cross-country mobility was pretty poor (it weren't no Churchill) so I'm not sure if it was ever used purely as an assault tank.

 

They started arriving in Europe at the end of Sept 1944 and the intention was that they should go to the Independent Tank Batts supporting the infantry in First (105), Third (90) and Ninth (60) Armies (yes the US Army in Europe couldn't add! Or was optimistic in its projections of what it was to receive). Tracking their actual allocation has proved difficult as official records make little attempt to differentiate holdings of M4A3E2 from ordinary M4A3(75). Initial allocations were to such batts.

Problem was "Everyone wants the M4A3E2". In Nov Third Army gave 5 of its first allocation of 40 to the 10th AD with more from subsequent allocations going to the 4th & 6th AD. It was the Armoured Divisions that wanted to use them as point tanks due to their ability to absorb hits.

But there are records that 743rd, 745th, 746th Tank Batts in First Army and 702nd, 712th, 735th, 737th & 761st Tank Batts in Third Army received initial allocations of 5 or 15 Jumbos in Oct/Nov.

Track grousers were a standard fitting for them in the field to help spread the ground load.