37mm Lend Lease Lost

[Mobius]

Someone on the Tanknet forum (WOT blog) posted data from Russian Archives on a few Lend Lease weapons. What is surprising was the data on the LL 37mm M5 gun. (Inserted data far right.) It seems the M51 shot virtually drops out of the sky (very high ballistic drag) because it loses speed so rapidly. In PCO the data for the 37mm M6 is from US sources. The M51 shot has a ballistic windscreen and it doesn’t lose velocity at anywhere near what the Russians were measuring. Even taking into account that the US measured the new round with 2900 f/s MV and the Russians must of gotten the old round with a MV of 2600 f/s there is a huge difference.

I also found something on another tech manual that indicated the windscreen of the M51 shot was threaded so was screwed onto the AP cap. Maybe the Russians didn’t have the windscreens attached to their rounds. Maybe they never made it to where the ammo was.

The only tank in PCO that uses the US 37mm is the M3 Stuart tank. And it doesn't appear very often. The gun would be over modeled if the Russians only received the early 2600 f/s round and didn’t have windscreens to the projectiles of those rounds.



The image on the left is the TM 9 1907 graph of the MV 2900 f/s ballistic curve. The green line shows what it would be for the same round with a MV of 2600 f/s. The blue line is a graph of the 37mm data from the Russian Archive.
In the right image the green line shows what the penetration of the 37mm round with MV of 2600 f/s would be with a windscreen. The blue line shows what the penetration would be using the Russian Archive data. The red line is taken from a graph of gun penetrations found at the Russian Battlefield website. This matches pretty closely with the blue line. So it may not be just a fluke that the Russians are measuring the 37mm M51 round without windscreens.

[Mobius]

I was wondering why the 37mm US penetration is so much higher than the Soviet (Russian Battlefield data)penetration. This can't be normalized by just multiplying one or both values by a small factor.

First to explain – every army had a different but often similar way of expressing armor penetration. The US seems to have had at least two during WWII. The method is to find the velocity limit where a plate is defeated. These are the Naval Ballistic Limit (NBL) and the Army Ballistic Limit (ABL).
The Navy criterion which demands that at least half the weight of the projectile shall pass through the plate.
The Army criterion which requires only that light shall show through the hole in the plate when the shot is removed.

I now have some US technical manuals with the actual ballistic limits of this gun. If I plot the points of the velocities where plates are penetrated I get some surprising results.
Plotting the points from the tables on to the graph of NBL 37mm M51 shot.
1) Blue squares are NBL values.
2) Purple diamonds are ABL values from upper right table.
3) Green and cyanic circles are ABL values and are from lower right table.

What is shows is that the plots for 0° incident angle penetration for ABL and NBL are indistinguishable.
That really shouldn't happen. The NBL should always be lower than the ABL. Armor of various hardness was tested and maybe that was normalized. Maybe armor thickness over shot diameter was also normalized. But it does look like the full penetration data is very optimistic.

Almost all the charts and graphs that appeared in WWII are for the NBL. A study in 1958 on wartime tests actually found that there was much more consistent testing done with the ABL.

I used to think there was something wrong with Russian data. Now I wonder about US data.

[Yoozername]

Does this square with this info you posted before?

[Mobius]

The 37mm (lowest line) is what I based the red curve line in the upper right panel of the first post.

I had to read through a number of WWII pdfs but found some surprising things. That the US tested their guns on a variety of different armor plate hardnesses (BHN) for the same thicknesses unlike probably the Germans and Russians. But then they normalized the result to what the penetration would be for a hardness of 237 BHN (115000 tensile strength). Which is not the best for armor plate.

This a post WWII review of some of the tests.
http://www.dtic.mil/dtic/tr/fulltext/u2/301343.pdf

[Yoozername]

http://www.ebay.com/itm/WW2-WWII-M51-37 ... 2ec6c0b1ed

Does look like it screws on to me.

[Yoozername]

That report looks like it is from Vietnam???

The data above in post #2 is very interesting in that it shows 1 inch plate of Brinnell hardness 402 being tested at 0, 20 and 30 degree angles. Just sloping or obliquity of 30 degrees seems to require over twice the KE. The 37mm does have a caliber to thickness advantage on a one inch plate (25.4mm). It's amazing how much protection that sloped armor gives. The hardness seems to be a factor as this seems to fall off with the first three tests of 1 inch armor.

I am referring to the chart on the lower right in post#2.

[Mobius]

ORIGINAL: Yoozername
That report looks like it is from Vietnam???
I am referring to the chart on the lower right in post#2.

No 1950ish, that comes from the same report that I found the graph.

Handbook of Ballistic and Engineering Data for Ammunition. Volume 1.
I guess it can be dl'd from scribed.

[Yoozername]

No, This is from Vietnam...

This a post WWII review of some of the tests.
http://www.dtic.mil/dtic/tr/fulltext/u2/a955097.pdf

Perhaps you mean this...

http://www.dtic.mil/cgi-bin/GetTRDoc?AD ... tTRDoc.pdf

[Mobius]

I corrected it.
http://www.dtic.mil/dtic/tr/fulltext/u2/301343.pdf

[Mobius]

ORIGINAL: Yoozername

http://www.ebay.com/itm/WW2-WWII-M51-37 ... 2ec6c0b1ed

Does look like it screws on to me.

http://www.inert-ord.net/usa03a/usa5/37mm/index.html
It apparently was alumimun as well. Maybe the Russians thought it more effective to melt down the caps and make aircraft from the alumimun than to shoot it at the Germans.
They got quite a lot of it in Lend Lease.

[Yoozername]

The Soviets would have been better off taking the turrets off the M3 and M5 tanks and melting them down.

The Soviet 45mm was a much superior weapon as far as AP or HE. Even the Germans used them on command halftracks. Perhaps not easily adapted to the 'Stuart', but perhaps something like a 20mm autocannon might have been more usefull. Actually, just taking off the turret and using as a APC or tractor might have been even better.

The Soviets, like the USA, held onto the light tank theory for quite awhile. They liked the Brit tanks with the 57mm. The Stuart just didn't cut it. Not sure if the Soviets received M-8 armored cars.

[Yoozername]

ORIGINAL: Mobius

I corrected it.
http://www.dtic.mil/dtic/tr/fulltext/u2/301343.pdf

Amazing information there.

[Yoozername]

37mm AP {test shows constant armor thickness and constant hardness of RHA with armor angle varied}
deg. inch. hardness. velocity. (?) notes

30 1.50 255 1617 6R(179) 7 SI&S
37mm attack 1.5 inch RHA @ 30 deg.
'Energy'=2614689

40 1.50 255 1808 2R(28) 6
37mm attack 1.5 inch RHA @40 deg.
'Energy'=3268864

45 1.50 255 2212 2R(36) 6 SI&S
37mm attack 1.5 inch @ 45deg
'Energy'=4892944

It takes 1.87 times the energy to attack a similar plate at 45 degrees than 30 degrees. This is for a M74 37mm AP round (pictured below). Just going from 40 deg to 45 deg yields an extra 50% more energy needed to penetrate the 45 degrees! This has to be such an enormous payoff compared to the amount of armor and space it would take. The Germans thickened the side armor on Panthers in the G model since they reduced the angle of the side armor itself to fit the new design. I bet it wasn't worth it. But this is for an uncapped round.

[Mobius]

What is kind of nice is the information in the form of tech manual pdfs are available online. What used to take going to Aberdeen, getting librarians to retrieve and rifling through all number of old reports can be found by most anyone. I found this as well.
http://www.dtic.mil/dtic/tr/fulltext/u2/310022.pdf

Which may be the data and formulas Nathan Okun used to develop his M79APCLC program.

I plotted out many of the points from it and the Naval Limits do differ by from 65%-88% from the Army Limits on the 301242.pdf. So there is no confusion between ABL and NBL of the 3" M79 shot.

[Yoozername]

ORIGINAL: Mobius





http://www.inert-ord.net/usa03a/usa5/37mm/index.html
It apparently was alumimun as well. Maybe the Russians thought it more effective to melt down the caps and make aircraft from the alumimun than to shoot it at the Germans.
They got quite a lot of it in Lend Lease.

It appears they got 3 different 37mm AP rounds? M51, M74 and M59? I suppose these are plain AP, AP capped and AP capped and ballistic capped (maybe not in that order)? These would be used in the M3 stuart (they turned down the M5) and M3 Lee. Not sure if the 37mm ATG was also supplied to them or what they thought of it.

The ammo listed also is for the Aircobra 37mm. These were separate ammunition types and lower velocity. Supposedly, the Soviets liked this aircraft. They also got the AA halftrack, M15A1 MGMC (37mm AA).

http://p63kingcobra.com/m4_37mm_auto_cannon.html

The US tanks also presented fuel issues and the Soviets liked things simple. The Brits made diesel 'Stuarts', not sure if these were delivered to the Soviets.

[Mobius]

These are the 37mm shot sent the Soviets. The M59 was used in the 37mm automatic cannon. It has no windscreen and lost velocity rapidly.

[Yoozername]

You're right. The M59 was used in the 37mm AAA halftrack. The Aircobra (or SuperCobra?) was not supplied AP ammunition (M80) so if it was used as a tank-buster, it was firing HE.

M80



Edit: Supposedly, the US only sent over a handfull of 37mm and 57mm ATG. So, the majority of the 37mm M51/M74 ammunition supplied would be for the tanks, M3 Stuart and M3 Lee. That is a lot of ammunition for a couple thousand tanks.

The US sent over 37mm/50 cal. AAA halftracks and also 37mm AAA guns. Maybe 100 halftrack and a few hundred guns.

It seems that the 37mm autocannon used in planes had no AP. The M80 round pictured above may have been a 'cap-less' M51 or M59 projectile.

The plane cannon rounds are obviously used specifically in the 37mm autocannon. The AAA 37mm appear to be longer brass and similar to the ATG rounds but they have lower charges and velocities.

I suspect that after the tanks were used initially, they were put in quieter areas. The AAA weapons were needed and they probably liked the M15 halftracks and perhaps modified other vehicles to take the ground mounted version. Perhaps they should have taken the Stuart turrets off and mounted the 37mm AAA gun atop it to give it tracks.

[Yoozername]

Similar info in a readable form. Interesting to cmpare how the ammo was doled out by the USA.

[Mobius]

The British got a mixture of AP shot types. That is why sources differ so much when they describe the effectiveness of the shot.

Here is some sources for the 37mm penetration:

"Anti-Tank Weapons" Peter Chamberlain and Terry Gander, MacDonald and Jane's, 1974
37mm M3A1 AP 1000yd 25mm @20º
APC 1000yd 53mm @20º

Tank Battles in Miniature: A wargamer's guide to the Western Desert Campaign 1940–1942", Donald Featherstone, Patrick Stevens Ltd, 1973,
37mm 1000yd 29mm @ 0º

"British & American Artillery of World War 2", Ian V. Hogg, A&AP, 1978.
37mm M3 AP M74 500yd 36mm 0º
37mm M51B1/2 500yd 61mm 0º
37mm AA AP M59A1 500yd 25mm 0º

Not much fun out on the Western Desert if all your tank had was the M74 round.