The Jumbo Sherman- Why weren't all US tanks outfitted like this?

It seems to be a very rational move that could have saved US lives and many US tanks.

With 100-150mm forward armor, the Jumbo Sherman could defeat fire from most German Antitank guns and the fire from the typical Panzer IV. This came at a mild reduction of overall speed.

"Since the overall tank weight increased from 34.8 tons to 42 tons, all "Jumbos" were permanently fitted with extended end connectors, commonly referred to as duckbills. Fuel economy stayed the same with a range of about 100 miles, but speed decreased by 4 mph to 22 mph."

I found some very informative posts from TA on the Jumbo Sherman (2003 thread) and its uses:

 

That extra weight pushed the M4's Running gear to it's absolute limits.
The duckbill end connectors were required on even quite firm ground to stop it sinking, and they proved fragile. It was a bit of a lumberer really, not suitable to as many roles as more conventional M4's, mostly only really useful in the assault, and severely limited by that loss of mobility.

The main reasons more M4a3e2s weren't manufactured were the war winding down and the usual process of obsolescence. They were knocked up from May to July '44 by Fisher and reached Europe by Autumn of that year, only ever being accepted as 'Limited standard' (essentially 'Stop-gap'). Also by the time their handiness in the specific business of picking through Germany was tested, designers attentions had already turned to an assault version of the Pershing (with 11 inches of frontal armour! ). In the end, the requirement for either ran down, Pershing was more agile and about as heavily armoured, and who needs a Sherman wheezing along with an extra few tons of weight for Pacific amphibious assaults.

"Outfitted like this" implies that the Jumbo modifications were just some sort of Bolt-on kit that could be easily retrofitted, and that's not really the case. That monstrous turret alone was an entirely new device. Look for shots of it from above to see just how different it is to any other M4 turret.

~A

 

That is what I was thinking as well, the "Jumbo" made the VVSS suspension run literally "bottomed out", and the newer HVSS suspension alone added many hundreds if not thousands of pounds to the overall weight of the M4 in the W (Wet Storage) version.

The HVSS allowed for wider tracks, and smoother rides in the Wet storage 76mm versions. Added armor weight, added wet storage weight, and added suspension weight might just have doomed the whole undertaking.

 

Thanks for the good info, Poop. The German heavy tanks seemed to have similar weight related problems and I wonder if these issues were worth it.

At 42 tons, this tank is around the same class as the German Panther. Since it was often used at the spearhead of an assault, I don't see how it would be problematic to produce and ship far more of them into the European continent.

Instead of having only one or two per medium tank company, it may have been worth it to outfit one or two entire platoons with it.

 

Not to mention allied Operational Research of Sherman losses found most were being KOed from hits in the sides and rear. The Brits did some calculations based on their reports, concluded increasing the frontal armor of their tanks to withstand Pak 40/75mm L/48 type rounds would only increase survivability some 35% (if I recall correctly). They concluded it just made more sense to put a bigger gun in their tanks that would allow them to blow away their enemy in one hit than fruitlessly try to increase armor protection, especially considering it was near impossibly to fit enough armor on allied Mediums to withstand Panther and 88mm fire without seriously compromising the tanks speed, ground pressure and reliability, much as the Jumbo did.

 

Very interesting.

What I do know is that in Normandy and the Ardennes, the Panther still suffered heavy losses thanks to side hits even with it's "invincible" front armor. The close quarters further negated the Panther's strength in long range shooting and forward positioning.

 

Tanks in general will take more hits their two sides and rear armor than the front armor, though individually the front plate takes more impacts than any other individual side. The Panther had formidable frontal armor, but in general its very vulnerable side armor meant that a majority of allied AP shot would strike armor that it could go through. Combine with the fact turret sides had similarly weak armor, simply traversing your turret to engage a target to the side could open your tank up to a turret crew killing shot.

Tank battles were not one on one affairs, and often allied operations took place across fronts some 1-2 kilometers wide (at the smallest) and generally more. During these battles it was entirely possible for panthers to have their frontal armor facing the immediate threat to their front but have their side armor exposed to tanks spread out across that 2-5 kilometer front who would be 500-600 meters away with a shot on the side armor assuming there was a clear field of view and assuming they were not engaging targets to their fronts.

In general I think tanks flanks are much more open to fire than most people imagine, to simply move anywhere but straight ahead or behind tanks had to reveal their side armor to the enemy, though at varying degrees. I remember reading of one battle in the British sector in Normandy where a Sexton Self Propelled Gun was driving through a town where a confusing battle was occuring, the German and British tanks were all mixed up. The sexton bumps into a Panther (not literally) who proceeds to start to traverse its turret towards the sexton when a Firefly appears behind it (had been chasing the panther) and put a round into the back of the turret. Things could get quite fluid, especially in western europe where engagement ranges could get quite close.

 

I recall an interview with a Tiger commander (both I and II) who opined that (paraphrasing); "we could handle four or five Shermans, or T34s, sadly for us, there was always a sixth or seventh with which we could NOT deal!"

 

Watch that one Clint - a very hot potato, there are other threads on the old '5-1' business .

It has been said that the desert taught a few false lessons on frontal armour and it's usefulness - Many engagements there were head-on and long-range (which fed into a lot of technical thinking at a crucial mid-point), but in most all other theatres armour Vs Armour and ATG was a far more confused affair carried out at the shortish ranges Wokelly mentions. Think of the high volume of German losses in the Normandy counterattacks, reinforcing that the very act of counterthrust is likely to expose both flanks to destructive fire,and even the rear in the fluid motions of real men & machines.

But Armour thickness was somewhat less relevant for the allies by Normandy anyway. The Churchill had the thickest frontal armour of any mainstream WW2 tank, and it was still little genuine protection there.

Lets take a troop of Jumbos into the Bocage for instance;
At those ranges against HV guns the extra armour will likely make no real protection difference, if both sides were equipped with Tigers they'd still be getting shredded.
You'd also have a far less agile vehicle sinking into the ground and wheezing through hedgerows. Firefly was a far more valid weapon than Jumbo, give them more of them and yes, I think you might conceivably make some difference. But as ever in Tank design & production, the magic wand to make it happen wasn't just lying around.

~A

 

How many of these were produced? I have not heard of them? So I take then that they did not see much action?

 

According to Hunnicutt:
254 M4a3e2 ordered and delivered.

Don't get me wrong, they were considered a successful and useful device, but not the potential panacea mooted here. A decent enough tool for a specific job.

 

Weren't some also jury rigged in theater? Or are those included?

 

There were certainly a fair few semi-official field mods involving large extra sheets of plate (as TA mentions above), but I don't think you can really jury-rig an e2, it's a rather too substantial modification.

I see the MVTF is/has restoring/restored one, 'gor bless 'em:
YouTube - Jumbo Sherman test drive.
(Caddydave's videos always worth a shufti btw )

~A

 

How did the Jumbo Sherman differ from the Super-Shermans used by Israel & other nations post WWII?

 

The "Super Shermans" ran on the HVSS suspension for starters, the old VVSS suspension used on the oversized Jumbo was running bottomed out with the extra weight of the extra armor. That is one difference, I can think of right off the top of my head.

 

M50 & 51 were essentially the best or most up to date bits of Sherman available bolted together to serve a proper BFG in the form of the French CN 75/50 on the M50, and a shortening of another French piece to form the 105mm D1504 on the M51 (Those designations from a raddled memory, so don't trust 'em).

To cut a convoluted story short, the 'Super Shermans' (Or 'Ishermen') were all about the BFG, whereas Jumbo was all about increasing armour.

~A

 

Either way, if you hit a tank in it's track its out for the count. No mobility means you're a sitting duck, so other tanks, vehicles etc. can out manouver you and hit you in the very vulnurable rear

 

Aye, but you could call track vulnerability a fairly equal 'given' across any tank of the period, so something of a level playing field in that regard. Even Churchill's 'over-hull' track design, though noted as a potential disadvantage in early German technical assessments, was rarely found to be an excessive vulnerability by it's users (excepting the removal of the track-guards near the turret to prevent fouling there, but that wasn't an issue caused by enemy action).

I'd say the ultimate 'mobility' arbiter by the time Jumbo came along was reliability, something many of the big German cats never quite achieved, and Sherman had in spades - though it does perhaps say something that the Jumbo was pushing even that legendary reliability past it's substantial limits.

~A

 

While the Jumbo certainly had its place..such as the way Von Poop mentioned in leading a convoy..it really was another kinda sideways step for American Arm. There really wasnt a need for a "hugely armoured tank" what was really needed was a better gun.

Sure the Jumbo's short 75 was good vs. Paks and other lighter targets..it wasn't very useful vs. tanks...As well its reliability was compromised as Poop mentioned.

Again its a interesting and novel approach to a "battering ram" technique but rather mis-guided in my opinion.

 

About 250 of these M4A3E2 Assault Tanks, nicknamed the "Jumbo" were produced:

Armor added was; hull 100 mm, turret 150 mm. Resulting in 84,000 lb, 42 tons (42,672 kg) weight. Grousers added to track to improve ride. They originally had the 75 mm gun but some were replaced by the 76 mm once in Europe.

This was an "added armor" unit which was intended to be used against the Siegried Line. It retained the weaker VVSS suspension, and that extra weight really put that system under maximum strain. The newer HVSS suspension was employed on the "Easy Eight"; M4A3E8, and that one served well after the war ended. (Tanks of World War II; Duncan Crow, 1979)

The "Jumbo" wasn’t designed as a tank destroyer, it was designed to be an assault tank for taking on fortifications, not other tanks.