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I again hand over the keyboard to MG Barnes, the head of US Army Ordnance Branch's R&D department in WW2. The previous writing by him, post-war, discussed tank development; this document, however, focused on the guns mounted on those tanks.

Exactly why this memorandum was written is not explained. The date indicates it was after the "tank panic" of Normany was about over, so it may have been a little late for it to have been a 'witch-hunt' to discover why US tanks seemed to be undergunned: One would have expected such a document to have been demanded in July or August were that the case.

Anyway, I present the memorandum again without comment. The OCR didn't seem to like this document very much, so just click on the page images to expand.

Great Read, I love reading these old docs, keep them coming, Good Job,
Edited by jamesdoz, Jan 05 2013 - 14:54.

Great finds Chief!

Information on the experimental guns is interesting...


105mm T4 (predecessor to the T5E1): 42lb projectile, 2900 ft/s muzzle velocity, 5.5 inches of penetration at 30 degrees angle and 2000 yards range.

That's a 19.07 kg projectile at 884 m/s muzzle velocity.

That doesn't match up with the 105mm T5, which fired a 17.69 kg projectile at 914 m/s muzzle velocity, suggesting those were changes made with the T5.

5.5 inches of penetration at 30 degree angle.

5.5 inches = 139.7mm
Converting that to 0 degrees penetration = 175mm
Converting that to 100 meters range (using probably figures for a ballistically capped shell of that caliber and energy) = 219mm

That's strangely high compared to figures for the 105mm T5, which is in the 195-200mm range in testing. It is however, consistent with other USA guns like the 76mm M1A1 and 90mm M3.


Next is the 90mm T15... 3200 ft/s muzzle velocity, which converts to 975 m/s, confirming that as the right value for the T15.

Interesting the mention about 90mm re-boring of the 105mm T5, with 24 lb projectile at 3500 ft/s. That's a 10.90 kg shell (same weight as the 90mm M77 AP, and close to the T33 APBC and M82 APCBC), at 1067 m/s muzzle velocity.
I don't know of any other USA gun of 1945 reaching that muzzle velocity with standard steel AP projectiles!

The document doesn't name that version of the T5 though, which is a shame.


Lastly there's the 155mm Gun Howitzer mounted on the T30. 95 lb AP projectile that could penetrate 6 inches of armor at 30 degrees inclination at a range of 2000 yards.

That converts 43.13 kg projectile weight, matching the source I had for that gun.

6 inches = 152.4mm

Converting that to 0 degrees penetration = 185mm
Converting that to 100 meters range (using probably figures for a ballistically capped shell of that caliber and energy) = 232mm
Edited by Zergling, Jan 05 2013 - 15:38.

Great post Chief !

great read! though i do wish we could fire 2000 yards accurately in game now... whats that 1828.8m?
Edited by Wulfshark, Jan 05 2013 - 16:42.

Interesting, and definitely useful.

wow that's neat! is it odd that when I'm reading this I'm thinking "Oh! I almost have that tank (T29)!!" Makes me feel .. special xD

So by the numbers on this page and using a relative armor calculator the 105 on the T29 should have 278mm of pen at 2000 meters vs armor at a 90. I want my 278 pen for my T32


The US 155 on the T30 should actually have 304 mm of pen on a 90/

If my math is right.

I bet Campbell sent a letter back to Barnes saying "cool story bro".

I sincerely hope Wargaming gave you a nice holiday bonus or a New Year's raise. You've earned it.

I wanna 90mm on the M10

Dark_Eagle, on Jan 05 2013 - 16:59, said:

30 degrees from vertical, not horizontal.

It certainly seems that MG Barnes didn't work and play well with the infantry branch (the using service)... although from the sound of it I don't think I'd be able to either.

no wonder the M3Lee, melee, sucks! I always wondered why would they put the more powerful gun NOT on the turret. Thanks to this document, I can now go die in a Melee in peace......lol

good stuff Chief! I could always see that there was nomenclature difference for the 3" and 76mm and the separation became obvious after a while. But, I always wondered if it was planned or just us (Americans) not agreeing on standard or metric.

Because the Ordanance Department wrote it, I would expect it to put them in the best light

But it does sound like they had a better handle on what guns the Army needed than Field Commanders.     My guess is the Field Commanders were still stuck in the mindset that tanks were infantry support weapons and didn't grasp the concept of modern mechanized warfare yet.

To give them credit, they had been trained in an army of infantry and cavalry.   In most wars, when there has been a dramatic change in technology and tactics, it takes a long time for some Generals to catch up.

I want more information on the 90 mm gun and the earlier T20 program (T20, T23). Can the T20 and T23 turrets have the 90 mm fitted? Where there plans of T20/23 based tank destroyer? If so what where they like? Is the T25 TD an accurate representation of a T23 based TD? etc.

Somewhat surprising to see an endorsement of the T30, given the vehicle's size, weight, mobility, and rate of fire problems. I guess its from optimistic reports like this that the M103 was born.

Also, from my reading of it, shouldn't T29 have a 90mm with the same visual model as the 105mm? Or am I misreading it?

Hammer_757, on Jan 05 2013 - 21:43, said:

It's the same logic as behind the 17-pdr/77mm/3" CS, even though the barrel was the same diameter on all 3

While this document and the one previous are a very intersting read they definitely look like this person is trying to take full credit for U S Tank development immedietely prior to and during World War Two.


Ut would be very intteresting to see some documents that are not as biased in the writers favour as these.

Kharsis, on Jan 06 2013 - 10:31, said:

I think you are reading more into this letter than necessary and in reality, politics played more of a role in weapon developement than actual field requirements.