# Up-armored M-10 and M- 36 tank destroyers: how much is too much?



## tomo pauk (Mar 18, 2013)

People,
The US Army was up-armoring some of their M4 Shermans into the tanks nick-named as Sherman Jumbo, with front and turret protected at Tiger-like levels. So how much would the tank destroyers (and their British siblings) been able to receive? Maybe going for HVSS suspension and wide tracks, in order to have a still maneuverable vehicle?


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## Shortround6 (Mar 18, 2013)

M-10s were _supposed_ to be able to be fitted with extra armor. That's what all those "studs" were for on the hull and turret. 







I have no idea how many sets of extra armor were manufactured (if any) but I don't think any were ever used in combat. 

Since the M-10's gun had the same performance as the 76mm Sherman I am not sure what the up armored M-10 would get you? Open turret if not upgraded and NO power traverse. No co-ax machine gun. Slugging it out with a Tiger was always going to be a loosing proposition until the 90mm M-36 showed up.


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## tomo pauk (Mar 18, 2013)

Up-armoring the M-10 gives the TD a better chance to shrug off the most common threat, namely the 7,5cm L43/46/48. The M10 was fielded, prior 1945, in far greater numbers than M4 with 76mm.


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## davebender (Mar 18, 2013)

U.S. Army doctrine stated tank destroyers were supposed to be fast. So I cannot imagine their being fitted with additional armor at the factory. This is something army workshops would need to do themselves when Ordnance Department inspectors weren't around.


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## tomo pauk (Mar 18, 2013)

Doctrines were there to be adhered until changed. See self-protecting bombers, or two-seater fighters. The doctrine was against 76mm armed Shermans, yet that was changed later.
Further, neither M-10 nor M-36 were fast, that was only M-18. So the M-18 stays as it is (fast tinclad), the other two receive additional steel.


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## davebender (Mar 18, 2013)

Much later. 

Most Sherman tanks were still armed with moderate velocity 75mm cannon during summer 1944.


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## tomo pauk (Mar 18, 2013)

The time line for the 76mm Shermans should start 1st with orders, then development, testing, production, transit over Atlantic, training, deployment in France... So the orders were given when, about a year before Overlord? No wonder most of the Shermans in action were of the 75mm variant, prior 1945.


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## dobbie (Mar 20, 2013)

I always thought the whole TD concept was flawed from the beginning, not so much from the idea, but the execution. Until the M36, the TDs werent much more effective than the M4 Sherman. The M18 had the speed but not the best gun, and the M36 had the gun but not the speed. Uparmoring some of these weapons would involve a lot more than just bolting or welding on extra armor. The drivetrain, especially the final drives has to be robust in order to handle the extra load. Add to all of this the logistics of support for another tracked vehicle that youre having to ship across the ocean and it all adds up pretty fast. If McNair and the others had not been dragging their feet about the Pershing, we might have had it sooner, or maybe at least a 90MM Sherman. Wouldnt have solved the weak armor issue, but at least they would have stood a better chance against Panthers, Tigers and such.


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## Shortround6 (Mar 20, 2013)

The Uparmored Shermans did use a modified final drive I believe, lowering their top speed. 

The US tank destroyer concept or doctrine was flawed as they were seen as a separate force or formation that was _not_ supposed to work with the tank formations but independently. Once an enemy armor thrust was identified the tank destroyers, using their superior speed, were supposed to intercept/ambush it without the need for tanks. 

Unfortunately the execution _never_ seemed to come up to the idea, 37mm guns on 3/4 ton trucks offered too little firepower and not enough protection, the M-8 armored car was originally part of the tank destroyer development line, Mounting a modern French 75 on a Half track chassis wasn't quite the answer either. The M-10 and M-36 had gun power but were no more mobile than the standard tank. Only the M-18 offered both speed and firepower. It did rather well against "normal" tanks but the bar had been moving. The Panther had originally been identified as another "heavy" tank and not a _standard_ medium tank.


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## tomo pauk (Mar 20, 2013)

The up-armored Achiles could also provide a well protected, self propelled 17pdr. Kinda erzatz-Firefly, adding armor being easier than adding 17pdr to the Sherman?



dobbie said:


> I always thought the whole TD concept was flawed from the beginning, not so much from the idea, but the execution. Until the M36, the TDs werent much more effective than the M4 Sherman. The M18 had the speed but not the best gun, and the M36 had the gun but not the speed. Uparmoring some of these weapons would involve a lot more than just bolting or welding on extra armor. The drivetrain, especially the final drives has to be robust in order to handle the extra load. *Add to all of this the logistics of support for another tracked vehicle that youre having to ship across the ocean and it all adds up pretty fast.* If McNair and the others had not been dragging their feet about the Pershing, we might have had it sooner, or maybe at least a 90MM Sherman. Wouldnt have solved the weak armor issue, but at least they would have stood a better chance against Panthers, Tigers and such.



There is no another/new tracked vehicle, if we up-armor the M-10 and M-36.


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## Shortround6 (Mar 21, 2013)

Again, what is the real object here?

an ersatz heavy tank? 

If you up armor an M-10 to the level of the M4A3E2 Jumbo you are going to be down to the Jumbos level of mobility. You have no more firepower than the Jumbo if the Jumbo is refitted with a 76mm gun, in fact you may have less because the M-10 carried less ammo and had no power traverse. The only MG on the vehicle is the .50 cal on top. 
The 3in/76mm guns were a bit lacking in power by mid 1944. 

You can't out run the Germans, you can't out gun them.


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## tomo pauk (Mar 21, 2013)

Shortround6 said:


> Again, what is the real object here?
> 
> an ersatz heavy tank?
> 
> ...



I reckon it you ask what is real objective? I've stated that in post #3:


> Up-armoring the M-10 gives the TD a better chance to shrug off the most common threat, namely the 7,5cm L43/46/48.



If you're in the M-10 or M-36, you cannot out run the Germans anyway. Your additional armor might manage to shrug off the hit by Pz-IV, or StuG-III, or 7,5cm PaK, so you're able return fire. No such opportunity with historic TDs. If one has up-armored Achiles or M-36, he is in a good position to out-gun Germans in general.

The Jumbo with 76mm is sorta Bigfoot - people talk about it, was it ever fielded? Not that it wouldn't be an useful AFV. The 76mm Shermans have had 55 rounds on board, vs. 54 at M-10, so the ammo count is a moot point.


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## Shortround6 (Mar 21, 2013)

M-10s had a MAX of 50.8mm on the front of the hull and 25.4mm on the side of the hull and turret. German 75mm L43-48 will go through 85-90mm at 500 meters at 30 degrees. You are going of need a lot of extra armor, unless you just armor the front. TD's are supposed to be used from ambush, not bull their way forward. 

M-10s were _supposed_ to be good for 48kph (M-36s 40-42kph?) Shermans ranged from 42-48kph depending on model. The Jumbo was good for about 36kph. 

According to Jane's the 76mm Shermans were supposed carry 71 rounds of ammo (86 rounds in a 1953 Army manual?) Down from the 97 rounds carried by the 75mm armed tanks. 

You need the Achilles or M-36 to bring the gun power up. 

A few photos of the Jumbo with in WW II do exist, just google for them, "Jumbo with 76mm" brings up several.


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## tomo pauk (Mar 21, 2013)

Shortround6 said:


> M-10s had a MAX of 50.8mm on the front of the hull and 25.4mm on the side of the hull and turret. German 75mm L43-48 will go through 85-90mm at 500 meters at 30 degrees. You are going of need a lot of extra armor, unless you just armor the front.



Yep, seems 50-70mm of additional armor plates might do the trick? The Jumbo received anything between 40-100mm of armor, vs. the regular M4A3, weight cost being 6,5 tons (from 31.5 to 38 ). The M-10 starting from 29.5t.



> TD's are supposed to be used from ambush, not bull their way forward.



Two things interfere wit that. Supposed deployment usage rarely equaled with historical. Second thing is that all M3/M4 based TDs have had armor, so they were supposed to be able to take some hits and keep going. Problem with that is that Germans have long time ago phased out the cannons the TD's armor is supossed to work against. So either ditch the armor (= M-18; new design production, not from M-10), or upgrade the armor, so it can withstand the most common threat of second half of the war.



> M-10s were _supposed_ to be good for 48kph (M-36s 40-42kph?) Shermans ranged from 42-48kph depending on model. The Jumbo was good for about 36kph.



Think we can agree that, even when going 48 km/h, the M-10 was not some speeedy machine. The several extra km/h certainly will not help out if the German gunner has one in his sights.



> According to Jane's the 76mm Shermans were supposed carry 71 rounds of ammo (86 rounds in a 1953 Army manual?) Down from the 97 rounds carried by the 75mm armed tanks.



Yes, sometimes it pays off to look at sources other that WIkipedia. 



> You need the Achilles or M-36 to bring the gun power up.



No doubt that those TDs have had more chance to achieve kills. OTOH, in Europe there was still plenty of M-10s around. 



> A few photos of the Jumbo with in WW II do exist, just google for them, "Jumbo with 76mm" brings up several.



I've googled that, total of two wartime pictures come up under 'images' section of the search. It was more often sight than Centurion in ww2, but not more often than Pershing.
Hmm, Jumbo + 17 pdr, now that would be something.


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## Shortround6 (Mar 21, 2013)

The armor on the M-10 wasn't supposed to be for a tank to tank dual. It was supposed to stop shell splinters, small arms fire, and light weapons (20mm?) 25.4mm of armor won't stop 37mm AP shot at much under 1000meters. What 50mm AT guns would do to it doesn't bear thinking about. 

The speed isn't to "drive" out of enemy's sights ( that may only work in reverse) but to position the unit or individual vehicle in firing positions or to change firing positions or to withdraw. If you can't retreat faster than the enemy can drive you have little choice but to stand and fight. 

The entire US tank destroyer doctrine was built on mobility. Slapping a bunch of armor on the vehicles and slowing them down by about 25% is going to require a rethink and rewrite of the manuals.

There were plenty of M-10s but the gun was an identical ballistic match to the 76mm gun in the Sherman which was found wanting just a few weeks after D day.


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## tomo pauk (Mar 21, 2013)

Shortround6 said:


> The armor on the M-10 wasn't supposed to be for a tank to tank dual. It was supposed to stop shell splinters, small arms fire, and light weapons (20mm?) 25.4mm of armor won't stop 37mm AP shot at much under 1000meters. What 50mm AT guns would do to it doesn't bear thinking about.



The armor of M-10 was between 38 and 57mm in the front, well inclined. Too much for anything under 40mm, let alone the splinters, too little for 5 cm and above? 
I agree that side rear armor were of the variety you say.



> The speed isn't to "drive" out of enemy's sights ( that may only work in reverse) but to position the unit or individual vehicle in firing positions or to change firing positions or to withdraw. If you can't retreat faster than the enemy can drive you have little choice but to stand and fight.
> The entire US tank destroyer doctrine was built on mobility. Slapping a bunch of armor on the vehicles and slowing them down by about 25% is going to require a rethink and rewrite of the manuals.



The doctrine was calling also for the TDs to engage enemy tanks, therefore blunting the possible encirclements. If the TDs must run away from enemy tanks, that means enemy succeeded without shots being fired, and it is able to wreak havoc in the rear area. How is the towed artillery (from 75 to 203mm) able to run away?



> There were plenty of M-10s but the gun was an identical ballistic match to the 76mm gun in the Sherman which was found wanting just a few weeks after D day.



I agree that 76mm was not an over-achiever. For anti-armor task, it was a class above 75mm.


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## Shortround6 (Mar 21, 2013)

tomo pauk said:


> The doctrine was calling also for the TDs to engage enemy tanks, therefore blunting the possible encirclements. If the TDs must run away from enemy tanks, that means enemy succeeded without shots being fired, and it is able to wreak havoc in the rear area. How is the towed artillery (from 75 to 203mm) able to run away?.



The idea is to withdraw to another firing position and let them come to you. You should be several miles in front of the towed artillery. You fire several shots, withdraw several hundred yds (or move laterally behind cover) fire several more shots and keep repeating. Perhaps if in a good hull down position you could stay a bit longer. The "run away" part comes if your position is flanked. The unit next to yours has given way and the enemy is already starting to by pass you. Are you fast enough to get out of the pocket? or do you stand and fight to allow others to try to escape? 

In real life there were not always enough alternative firing positions and/or the terrain did not allow for easy movement between them.

The M-10 had a problem with turret traverse. 

Early ones looked like this.






Most of the ones that saw actual service looked like this:






The two "blocks" on the back of the turret were solid steel, not boxes, they were counter weights as the turret would up too nose heavy and being manual traverse had problems being trained (turned) on slopes. There were several different shapes of counter weight. Sticking hundreds of pounds of armor on the front of the turret would require several hundred more pounds on the back and some really strong gunners to rotate the turret.


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## fastmongrel (Mar 22, 2013)

I have often wondered why no power traverse on the M10. I can only imagine as it was a four man turret there wasnt the room.


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## tomo pauk (Mar 22, 2013)

M-36, photo probably taken during the liberation of Southern Dalmatia, Croatia, in late 1942. Boy, what a victory that was.

http://www.oklop.net23.net/m36/m36-1.JPG

Interesting hybrid, M-36 turret on M4 hull:

http://www.oklop.net23.net/m36/m36-23.JPG

More about the ex-Yu M-36, text pics, can be translated:

http://www.oklop.net23.net/m36/m-36.HTM


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## dobbie (Mar 22, 2013)

If we are stuck with what I consider to be a very flawed philosophy concerning TDs and tactics, the only TD which met the standard was the M-18, and it didnt have enough gun. Instead of all this additional armor which is going to slow down any vehicle you put it on, upgun the M-18 to 90MM so it can engage at ranges longer than knife fighting distances, and maybe put a roof on the turret in order to give some protection from airburst artillery and the locally tossed hand grenade.

Either that or up-engine the M-36. Seems wasteful to me to make 3 or 4 different TDs which you have to build, ship across the ocean and support. If speed and mobility is the criteria, then armor is going to be sacrificed. True, adding a 90MM is going to put on some weight to the vehicle, but not as much as putting on effective armor.


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## yulzari (Mar 22, 2013)

Tomo

These M36/M4 hybrids. Did they have the powered traverse of the M4 or the hand traverse of the M36?

The M36 had Russian T55 engines. Were any M4s so updated?

Were any ex British Achilles 17 pounder M10s? The British used these as self propelled anti tank guns like the Valentine Archer. I know the Achilles all had to be given back the the US after the war like the M4s.


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## tomo pauk (Mar 22, 2013)

The M-36B1 ('hybrid') was received from USA as-is, ie. it was not some kind of Yu modification. From what I can read at the article, only the M-36B2 (hull of M-10A1) were modified by adding the Soviet diesel engine. The M-18s were also updated like that.
The modification of the M4 was a failure, it was being tested with Yu copies of the V2 engines (as those used in T-34 and derivatives). It was being tried from 1964 , and terminated in 1966. Minister of defense said that M4s are to be used as-is, later eventually their parts to be used in M-36s, those regarded as more useful AFVs.
M4 with V2 engine:

http://img62.imageshack.us/img62/9302/m441.jpg

There were no Achiles in ex-Yu, not that I know about them.


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## Shortround6 (Mar 22, 2013)

When re-powering things like tanks you have to take the transmissions/steering gear into account. 

The V-8 Gas engine in the Sherman was good for about 450hp at 2600rpm. The diesel in the T-34 was good for about 500hp at 1800rpm. The power sounds like a good match but but it practice there are at least 2 sources of trouble. 

1. The Max governed speed of the gas engine is 2800rpm which equals about 26-29mph in high gear. The diesel doesn't turn as fast which means that unless you replace the final drive gears top speed will be limited to around 20-22mph? 

2. The max torque of the gas engine (an 18 liter engine) is 950ft lbs at 2100rpm. The diesel is making about 1460ft lbs at 1800rpm (and perhaps a bit more lower?). Gears and gear shafts don't really care about horsepower, they do care ( are affected by) torque. Increasing the torque the gears and gear shafts have to handle by over 50% is going to lead to a lot of blown transmissions.


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