Radial engines favored for powering the tanks & AFVs, 1935-45

German Engine compartment was pretty filled up, some pics grabbed from web search of a model


Maybach and the Radial would be fairly similar in length, and while wider, doesn't need all that liquid cooled radiators and plumbing

I'm not seeing easy spark plug access here.

Rear Doors?
Easy.
Relocate the exhaust a bit, and borrow this from the sd.kfz 251

and then borrow the US idea for sliding out the engine like with the M-18 on rails


While the Germans had issues making enough BMW radials, They could use the Gnome-Rhone 14N twin row engines, a bit longer, and narrower and shorter, from the captured factories in occupied France.

Much more displacement, so will still run on lower octane gasoline than 87 if the C/R is dropped a bit.

The air cooled engines are going to require some extensive ductwork/fans. compact size may something of an illusion.
I will note that the Engine used in the M-18 (and many other American vehicles was the R-975.
from Wiki,
"The Wright R-975 Whirlwind was a series of nine-cylinder air-cooled radial aircraft engines built by the Wright Aeronautical division of Curtiss-Wright. These engines had a displacement of about 975 cu in (15.98 L) and power ratings of 300–450 hp (220–340 kW). "
A large number were made under license by Continental.

Just because you can use a 450hp engine in one vehicle does not mean you can use the same size engine to replace a 600+HP engine in another.
The Whirlwind was a 45in diameter engine of around 650-700lbs depending on model. Fan assembly not included.

The BMW 132 was 54in dia and over 1100lbs, granted the G-R 14N was smaller but a 51in diameter engine was still big and at over 1300lbs it is certainly not light.
Now the US did try to use the Wright Cyclone in the M-6 heavy tank.

These things had the size (or were made big to hold) the 54-55in diameter engine.

marathag said:

While the Germans had issues making enough BMW radials, They could use the Gnome-Rhone 14N twin row engines, a bit longer, and narrower and shorter, from the captured factories in occupied France.

Click to expand...

Appeal of the radial engines used on the tanks was that they were light, compact, simple (both to make and to maintain) and powerful. The 14N was powerful, but as a 2-row radial it was not a simple engine anymore. It was longer than the 1-row radials. Forced cooling of 2-row radials is ought to be more compicated and will require greater volume than for the 1-row radials.

Germans can tap on the production of Mercury engines from Poland (plus the tooling for the Pegasus in both Poland and CZ). That gives them perhaps 600 HP on the 80 oct fuel?

Further - the 2-row radials have a strong competition from V12 engines. Germans can 'dumb down' the Jumo 210 engine for purposes of fitting it in a tank; the G&R 14N is far more useful as an aero engine than the Jumo 210.

Shortround6 said:

The air cooled engines are going to require some extensive ductwork/fans. compact size may something of an illusion.
I will note that the Engine used in the M-18 (and many other American vehicles was the R-975.
from Wiki,
"The Wright R-975 Whirlwind was a series of nine-cylinder air-cooled radial aircraft engines built by the Wright Aeronautical division of Curtiss-Wright. These engines had a displacement of about 975 cu in (15.98 L) and power ratings of 300–450 hp (220–340 kW). "
A large number were made under license by Continental.

Just because you can use a 450hp engine in one vehicle does not mean you can use the same size engine to replace a 600+HP engine in another.
The Whirlwind was a 45in diameter engine of around 650-700lbs depending on model. Fan assembly not included.

The BMW 132 was 54in dia and over 1100lbs, granted the G-R 14N was smaller but a 51in diameter engine was still big and at over 1300lbs it is certainly not light.
Now the US did try to use the Wright Cyclone in the M-6 heavy tank.
View attachment 822988
These things had the size (or were made big to hold) the 54-55in diameter engine.

Click to expand...

Studies were done to improve the Sherman very early, and one of the early thoughts was to use that big Wright from the M6 in t he M4, along with the track and suspension



So this M4X really should have been done, even though would be over 40 tons, and could have had the 3" gunpower of the M6 in a far more compact and lighter package. The Wright G200 'Dry' weight was 1350 pounds, the GAA was 1560 pounds. The Maybach HL210 was 2310 pounds. The heaviest engine was the Chrysler Multibank at 5400 pounds, that just edged out the GMC twin 6-70 install. at 5110 pounds.

But the main takeaway, is a big radial could be fit in this medium tank weight range, American or German using BMW or G-R power

tomo pauk said:

Appeal of the radial engines used on the tanks was that they were light, compact, simple (both to make and to maintain) and powerful.

Click to expand...

Lack of a liquid cooling system probably makes them simpler to maintain, although on a ground platform you need fan(s). Simple if you can just mount a big fan on the crankshaft, less so if packaging requires the fans to be placed elsewhere?

But simple to produce? As S Shortround6 likes to point out, manufacturers went through several iterations of the engine designs to increase fin density. And the manufacturing methods of the fins were also changed multiple times, some of which sound very labor intensive. A liquid cooled inline engine, in comparison, can make use of monobloc construction where only a few castings make up the major structural parts of the engine.

Looking at the unit costs of US engines, for $/hp there's a huge amount of variation but it doesn't seem as either engine type has a big advantage either way.

Further - the 2-row radials have a strong competition from V12 engines. Germans can 'dumb down' the Jumo 210 engine for purposes of fitting it in a tank; the G&R 14N is far more useful as an aero engine than the Jumo 210.

Click to expand...

Germany had several options that could have been developed into excellent tank engines. On the diesel side of the fence, for heavy tanks what about a V-12 version of the mid-1930'ies V-16 DB 602 airship diesel (used on the Hindenburg, for instance)? And do a V-8 version of it for medium tanks? Or somewhat later, the MB 507? For lighter tanks, there was the excellent Tatra 103 of which a variant remained in production for decades after the war as a truck engine (Tatra 111 - Wikipedia ).

z42 said:

But simple to produce? As S Shortround6 likes to point out, manufacturers went through several iterations of the engine designs to increase fin density. And the manufacturing methods of the fins were also changed multiple times, some of which sound very labor intensive. A liquid cooled inline engine, in comparison, can make use of monobloc construction where only a few castings make up the major structural parts of the engine.

Click to expand...

Engines consist from many other parts, too. A 1-row (and even a 2-row) radial needs a much simpler crankshaft, only two bearings*, only one carb (non-supercharged V12s sometimes used 2, 4 or even 6 carbs) while the crankcase is the only part needing to be cast. Number of small parts is also smaller, like the pistons, valves, wrists and pins, springs.

The predominance of 1-row radials on the aircraft made between 1925-35 is to be noted. Bristol, Wright and P&W, plus their licensees were everywhere, and a number of companies making liquid-cooled engines were switching to the radial engines' production. Granted, a good V12 on a new fighter is a better choice when that extra 10, 20 or 50 HP is required, together with that extra 10 or 20 mph, but bombers, transports and trainers were happy with radials of the day.

Need for extra finning was indeed there when the ~500 kg radial aero engines were pushed towards 800, 900 etc. HP, but for a tank engine, where a radial with 500 HP is a great choice, the tech of yesterday is still a good thing.

Specifically for the Germans, a V12 engine on a 20 ton tank strikes me as a luxury.
A radial on a Panther tank can save close to 1500 kg vs. the HL.230, the weight allowance better used to bulk up the side armor.

* that is the big end bearings, plus just one for where the crank throw is; compare with a V12 needing 7 bearings for the crankshaft laying in the crankcase, and 6 for where the crank throws are

tomo pauk said:

Engines consist from many other parts, too.

Click to expand...

Obviously, yes. My point was that considering historical engine costs were all over the map, you can't really say that a radial would be significantly cheaper to produce than an equivalent inline. Production productivity improvements driven by volume are probably more important, see e.g. Wrights law.

only one carb (non-supercharged V12s sometimes used 2, 4 or even 6 carbs)

Click to expand...

If you want to use more carbs for an inline, in order to get more even mixture, certainly the same applies to radials? Or you can just do what most radials did, have the mixture rich enough for the cylinder with the leanest mixture, and accept that the other cylinders run richer? Simplicity vs. fuel consumption is a tradeoff not unique to either type of engine.

while the crankcase is the only part needing to be cast.

Click to expand...

Indeed, and that's not an advantage. Casting is well suited for cost effective mass production. The more parts that need to be intricately machined, the more expensive the engine is going to be.

The predominance of 1-row radials on the aircraft made between 1925-35 is to be noted. Bristol, Wright and P&W, plus their licensees were everywhere, and a number of companies making liquid-cooled engines were switching to the radial engines' production. Granted, a good V12 on a new fighter is a better choice when that extra 10, 20 or 50 HP is required, together with that extra 10 or 20 mph, but bombers, transports and trainers were happy with radials of the day.

Click to expand...

Radials being a very good choice for aircraft, doesn't mean they are a particularly appropriate solution for non-aero use. Apart from the US WWII era tanks, which used radials largely due to failing to develop tank engines in the interwar period and thus had to resort to whatever was available off the shelf, you'll note a distinct lack of success of radials in ground vehicles, before and after WWII.

Specifically for the Germans, a V12 engine on a 20 ton tank strikes me as a luxury.

Click to expand...

I don't know. The Tatra 103 which I previously mentioned was used on armored cars and heavy trucks, certainly cheaper vehicles than a tank.

* that is the big end bearings, plus just one for where the crank throw is; compare with a V12 needing 7 bearings for the crankshaft laying in the crankcase, and 6 for where the crank throws are

Click to expand...

If you're going to include the crank pin journals for the V12, certainly you'll need to include the equivalent journals on the radial as well, as they'll need the same kind of conrod bearings (except for the master rod, of course)?

z42 said:

Obviously, yes. My point was that considering historical engine costs were all over the map, you can't really say that a radial would be significantly cheaper to produce than an equivalent inline. Production productivity improvements driven by volume are probably more important, see e.g. Wrights law.

Click to expand...

Quite true.
I don't like the chart in post #105 as there seems to be a lot 'errors' and/or contracts for development engines. 52 28 cylinder 4 row R-4360s contracted for in 1942? Delivered when?
But the V-770 is interesting about the same price as an Allison V-1710 of 2 1/2 times the power. The V-770 was supposed to be two Ranger 6 cylinder engines mounted on a common crankshaft. A pair of trainer engines with a small supercharger costing over 12 grand?

z42 said:

If you want to use more carbs for an inline, in order to get more even mixture, certainly the same applies to radials? Or you can just do what most radials did, have the mixture rich enough for the cylinder with the leanest mixture, and accept that the other cylinders run richer? Simplicity vs. fuel consumption is a tradeoff not unique to either type of engine.

Click to expand...

All but the small trainer engine radials used a small supercharger/mixing fan to get even fuel distribution.
As far as I can tell for the US the Jacobs, Kinner, Warner and Continental radials did not use an impeller in the induction system. The Lycoming R-680 did as did the 7 & 9 Cylinder Wright Whirlwinds (235-450hp) and the P&W R-985 and R-1340 all used a supercharger or at least a rotating impeller to help insure even distribution to the cylinders.
Simple fuel distribution was pretty much only used on low power (cheap) engines.

z42 said:

Indeed, and that's not an advantage. Casting is well suited for cost effective mass production. The more parts that need to be intricately machined, the more expensive the engine is going to be.

Click to expand...

There were also tremendous strides made in both casting and forging during the war in different countries. Ford figured out how cast steel cylinders instead of using forgings on the R-2800. This helped tremendously with both cost and rate of production BUT they used a machine that eight molds at a time on a rotating turn table that spun to use centrifugal force to get the molten steel go where they wanted in the molds and to help with the formation of grain structure in the casting. Without that expertise in casting and the ability to make such casting machinery other countries could not duplicate the method. US also used things like gang slitting saws to machine fins and when working on heads, each saw was controlled for depth by a cam following a profile on a master pattern. Each saw could cut to a different depth on the same pass across the surface. Even smaller US companies did not have access to much of the more sophisticated machines.

z42 said:

Radials being a very good choice for aircraft, doesn't mean they are a particularly appropriate solution for non-aero use. Apart from the US WWII era tanks, which used radials largely due to failing to develop tank engines in the interwar period and thus had to resort to whatever was available off the shelf, you'll note a distinct lack of success of radials in ground vehicles, before and after WWII.

Click to expand...

This is quite true. It can be noted that the US M-5 Light tank entered production in 1942 and used twin Cadillac car engines to replace the Continental R-670 radial engines (and the Guiberson radial diesel) According to Wiki................"This version of the tank was quieter, cooler and roomier" although the last part may be because they are comparing the sloped M-5/M3A3 hull to the more boxy but smaller M3/M3A1 hull.

z42 said:

I don't know. The Tatra 103 which I previously mentioned was used on armored cars and heavy trucks, certainly cheaper vehicles than a tank.

Click to expand...

It did give super range for recon cars
However it also shows some of the problems. I do think the Tatra 103 was very good engine for it's time. BUT, it was a 14.82 liter engine running at 2250rpm for 220hp vs the standard MK III/IV Maybach HL 120 of 11.86 liters running at 3000rpm for 300hp. Italians needed a 25 liter V-12 diesel to get 330hp in the 26 ton P-26/40 in 1943. Japanese were using a 21.7 liter V-12 at 2000rpm to get 240hp. The Tatra, the Italian and Japanese engines were all (?) air cooled.
Diesels are fuel efficient but they were large and heavy (usually) for the power provided.

z42 said:

If you're going to include the crank pin journals for the V12, certainly you'll need to include the equivalent journals on the radial as well, as they'll need the same kind of conrod bearings (except for the master rod, of course)?

Click to expand...

P&W R-2800 master rod. The eight other rods are mounted on pins and bushings/plain bearings in the eight holes in the master rod. In a way it is simpler. On the other hand on the R-2800 you can be transmitting 1000hp (or more) through a single bearing and crank journal.

z42 said:

Apart from the US WWII era tanks, which used radials largely due to failing to develop tank engines in the interwar period and thus had to resort to whatever was available off the shelf, you'll note a distinct lack of success of radials in ground vehicles, before and after WWII

Click to expand...

The lack of success with using radials in ground vehicles was due to packaging.

An inline is easier to incorporate into a vehicle's design than a radial both in dimemsions and crank output position.

The advantage to an air-cooled radial, is that they don't need to be run at high RPMs to generate sufficient horsepower as well as eliminating a cooling system and all that is involved.

An AFV's cooling system required a robust design that would tolerate shocks such as discharging rounds from it's main weapon as well as absorbing impacts from enemy counter-fire.

marathag said:

...So this M4X really should have been done, even though would be over 40 tons, and could have had the 3" gunpower of the M6 in a far more compact and lighter package. The Wright G200 'Dry' weight was 1350 pounds, the GAA was 1560 pounds. The Maybach HL210 was 2310 pounds. The heaviest engine was the Chrysler Multibank at 5400 pounds, that just edged out the GMC twin 6-70 install. at 5110 pounds.

But the main takeaway, is a big radial could be fit in this medium tank weight range, American or German using BMW or G-R power

Click to expand...

I respectfully disagree with this premise. There were several major issues with each of these individual components that when combined make this hypothetical M4X an impractical war-fighting tank.

• The Wright G200 wasn't a sufficiently mature engine for a tank installation in 1942 (or, frankly, even by the War's end) and suffered a myriad of reliability and supposed maintainability issues. These were prolific during the M6 program (low Mean Time Between Failure, susceptibility to failure under rapid engine loading ala the R-975, etc.) and while a lot of the teething issues might've been resolved with more time and resources, there's no free lunch in engine design, and the impressively light construction of the G200 came at the expense of its operational reliability (as an aside, but such reminds me far too much of the story with the troubled AVCR-1360 some 30 years later).

• The 3" M7 was deemed unsatisfactory in the existing M34 mount and 'small' Sherman turret arrangement. This was a determination Aberdeen also came to in 1942, and other issues persisted such as the unsatisfactory blast characteristics of the M7, the relatively high mass of the gun and mount (which limited its use in conjunction with the Sherman's gyro-stabilization system, as well as straining the powered traverse). Of course none of these factors prevented it from being installed in the M10 GMC, but that was in an open-top and unpowered mount. What the Army ultimately wanted was the 76mm M1 gun combined with an enlarged and redesigned turret (as seen through the M4E6 program with installation of the T23 turret), and by that point you've got 460-HP R-975C4s and 500-HP Ford GAAs in a ~32,500 kg tank, which is both more reliable, usable, and better-armored* (*from the front) than the hypothetical M4X.

• The suspension unit derived from the M6 tank was prone to excessive failure. It wore out too quickly, provided poor steering characteristics and was quite heavy compared to existing VVSS suspension on the M4A1s in-service. Eventually, of course, the M4 would improve upon the M6-derived suspension lineage with the 1944-vintage HVSS suspension, which resolved all of the key issues previously noted (barring weight, as it was still considerably heavier than the VVSS, even with the all-steel T66 track).

In the end, while it is fun to theory-craft and re-imagine existing vehicles in-theatre, I think the US made the right decision in sticking with the Sherman as it was instead of going for a fundamentally new design. After all, the tank the Army ultimately wanted was eventually received with the M4A3 (76) HVSS, while being smaller, lighter, and sharing greater part interchangeability amongst older Shermans than an 'M4X' would.

Anyways, those are some thoughts about the idea, hopefully I didn't come off as too brash as it isn't my intent to butt heads over such a matter.

Think Tanker said:

The Wright G200 wasn't a sufficiently mature engine for a tank installation in 1942

Click to expand...

Honestly, Wright had problems with all their engines. GM/FORD/Chrysler would have fixed that, had desire for more large engines been contracted out, as it took Dodge, never having built any aircraft engines, redesigned much of the R-3350 to be reliable, while Wright flailed about

Think Tanker said:

The 3" M7 was deemed unsatisfactory in the existing M34 mount and 'small' Sherman turret arrangement

Click to expand...

Luckily, the M4X did not have the original 'small' M4 turret, but did have carriover of the M34 mount, that was being improved to the M34A1, and an M4X would have had something different from that, to allow use 75mm/3"/105mm option as contract demanded. Later would have had changes to the turret to add in the all vision cupola and Loaders hatch, as happened with all later M4 production.

yes, the 3" was hardly perfect, being a WWI retread, but it existed in 1942. Just turned out that the 3" and the M1 90mm were very close in weight, leading to the M6 testing and then M10-->M36 that added powered traverse. I feel that the no Traverse motor on the M10 was some more McNairism that crept into the TD design.

A case could be made for this TL that the 76mm gun project would never happen if it's a 3" to 90mm progression in the medium tank line

Think Tanker said:

The suspension unit derived from the M6 tank was prone to excessive failure

Click to expand...

True, in the 77 ton M6. Would have far less stressed for moving a 40 ton tank around, and nothing stops the development of that 1941 era HVSS to what was done later for the various T2X series prototypes before being used for the E8 on the late Shermans after 1944

In 1942, the US was on target from having too much floor space allotted for Sherman production

EDIT: wow, this chart did not import well.
EDIT2 : much better
and those companies did not have M4 contract renewed in 1943
Some could have been allocated for doing the M4X, esp. the one that didn't have extensive casting facilities like the Locomotive producers.
list of producers, by amount of production
Detroit Tank Arsenal
American Car & Foundry
Fisher Tank Arsenal
Cadillac Motor Company
Pressed Steel
Pullman-Standard
American Locomotive Works
Baldwin Locomotive Works
Massey Harris Company
Ford Motor Company
Lima Locomotive
Montreal Locomotive Works
Marmon-Herrington
Pacific Car and Foundry
Federal Machine&Welder
Rock Island Arsenal
International Harvester, Burlington Arsenal

So the US could have made the regular M4, plus the M4X in lower number, if there was a engine supply problem. Originally, there were plans for 1000 M6 Heavies to be made, and the M4X could have done much of what the 'Heavy' was supposed to have done with the doctrine in place over 1941-2

GrauGeist said:

The lack of success with using radials in ground vehicles was due to packaging.

An inline is easier to incorporate into a vehicle's design than a radial both in dimemsions and crank output position.

Click to expand...

Undoubtedly, at least partially. But considering the utter dominance of inlines these days (straight, V, and a smattering of boxers thrown in here and there for good measure) in practically any application, maybe there's something else as well? Maybe those engine configurations just lend themselves well to producing cost-effective, reliable, and maintainable engines?

Though maintainability at least partially overlaps with packaging. A radial may work fine in an aircraft installation, where you have (somewhat) easy access to the engine from any direction, but in an engine bay in a vehicle, not so much.

The advantage to an air-cooled radial, is that they don't need to be run at high RPMs to generate sufficient horsepower

Click to expand...

Max RPM is probably more due to the stroke length together with the RPM determining the piston speed and thus internal engine loading etc., rather than something due to the cylinder configuration. Hence bigger engines generally have a lower max RPM. Air-cooled engines may have additional considerations due to cooling, no point running at higher rpm if it means you cannot keep the temperature within limits.

Yes, in the WWII era radial aero engines generally ran at lower rpm than inline aero engines, but inlines used in tanks generally had much lower rpm than inline aero engines. The German Maybach engines were somewhat exceptional in running at high rpm.

An AFV's cooling system required a robust design that would tolerate shocks such as discharging rounds from it's main weapon as well as absorbing impacts from enemy counter-fire.

Click to expand...

There are certainly advantages to air cooling. As well as disadvantages. Looking at post-WWII AFV's, except for the undoubtedly successful air-cooled AVDS-1790, and a few turbine powered tanks, it seems most AFV's have used water-cooled diesels.

7 M7 Medium Tanks built December 1942 to February 1943, 1 M6 Heavy Tank in December 1942, then 39 March 1943 to February 1944, 1 T23 Medium Tank in November 1943 then 249 January to December 1944, 40 T25 Medium Tank February to May 1944, batch of 10 M26 heavy Tank February to May 1044 then production from November.

385 American loco M3 Lee Jun-41 to Aug-42
300 American loco M3A1 Lee Jan to Jul-42
84 Baldwin M3 Lee Jul-41 to Mar-42
211 Baldwin M3 Grant Oct-41 to Mar-42
2 Baldwin M3A2 Lee In Jan-42
210 Baldwin M3A5 Lee 1 in Jan then Apr to Dec-42
10 Baldwin M3A2 Grant Jan to Mar-42
381 Baldwin M3A5 Grant Feb to Jul-42
239 Baldwin M3A3 Lee 1 in Mar then Jul to Dec-42
83 Baldwin M3A3 Grant Apr to Jul-42
3,243 Chrysler M3 Lee Jul-41 to Aug-42
109 Chrysler M3A4 Lee June to Aug 42
501 Pressed Steel M3 Grant Aug-41 to Jul-42
500 Pullman M3 Grant Aug-41 to Jul-42

150 American loco M4A2 75mm Sep-42 to Feb-43 plus 1 in Apr-43
2,150 American loco M4 75mm Feb to Dec-43
12 Baldwin M4A2 75mm Oct/Nov-42
1,233 Baldwin M4 75mm Jan-43 to Jan-44
7,499 Chrysler M4A4 75mm Jul-42 to Sep-43
1,676 Chrysler M4 75mm Aug-43 to Jan-44
75 Chrysler M4A6 75mm Oct-43 to Feb-44
800 Chrysler M4 105mm Feb to Sep-44
1,400 Chrysler M4A3 76mm Mar to Aug-44
500 Chrysler M4A3 105mm May to Sep-44
2,617 Chrysler M4A3 HVSS 76mm Aug-44 to Apr-45
841 Chrysler M4 HVSS 105mm Sep-44 to Mar-45
2,539 Chrysler M4A3 HVSS 105mm Sep-44 to Jun-45
540 Federal M&W M4A2 75mm Dec-42 to Dec-43
4,614 Fisher M4A2 75mm Apr-42 to May-44
2,420 Fisher M4A3 75mm Feb to Dec-44
254 Fisher M4A3E2 75mm May to Jul-44
1,594 Fisher M4A2 76mm May to Dec-44
525 Fisher M4A3 76mm Sep to Dec-44
651 Fisher M4A3 HVSS 75mm Jan to Mar-45
1,300 Fisher M4A2 HVSS 76mm Jan to May-45
1,690 Ford M4A3 75mm 1 in Jun-42 then Aug-42 to Sep-43
1,655 Lima M4A1 75mm Feb-42 to Sep-43
188 Montreal M4A1 75mm Oct to Dec-43
926 Pacific Car M4A1 75mm May-42 to Nov-43
3,700 Pressed Steel M4A1 75mm Mar-42 to Dec-43
1,000 Pressed Steel M4 75mm Jul-42 to Aug-43
3,426 Pressed Steel M4A1 76mm Jan-44 to Jul-45
21 Pressed Steel M4A2 HVSS 76mm Apr/May-45
2,737 Pullman M4A2 75mm Apr-42 to Sep-43
689 Pullman M4 75mm May to Sep-43


Halfway point for Sherman production reached during September 1943, by year 8,017 in 1942, 21,433 in 1943, 13,179 in 1944, 6,793 in 1945, the US Army was planning larger armoured forces plus more troops in combat in 1943.

Early production M4 with 75mm were manufactured with the M38 Telescope with M4 Periscope, then went to the M55 Direct Telescope and the M38/M4, and finally the M70F Direct Telescope and the M38A2/M4A1 Periscope (M4A3).

The M4A3E2 was manufactured with the M71G Direct Telescope and M38A2/M4A1 Periscope.

M4 76mm were manufactured with the M71D Direct Telescope and M47A2/M4A1 Periscope.

The M71-series was designed for the 76mm, except the "G" which was a one-off modification designed for the 75mm in the M4A3E2 since that tank utilized a modified version of the 76mm gun mount and shield. The M70-series was for the 75mm, again except the "G" which was utilized in the M10. The ultimate 76mm sight during the war was the M71F ("E" reference not found) and for the 75mm it was the similar M70F. The M71F didn't become available until fall 1944 in production and in limited quantities for retrofitting to existing vehicles.

It bears remembering that there were a large number of Sherman types, they breakdown roughly as:
Early Production - all with dry stowage
M4 75mm, rolled glacis at 56 degrees, 2-inches thick, driver and co-driver "hoods" act as weak point and shot trap
M4A1 75mm, cast hull of highly variable quality, 37-56 degrees, 2-inches thick, driver and co-driver "hoods" act as weak point and shot trap
M4A2, M4A3, M4A4 75mm rolled glacis at 56 degrees, 2-inches thick, driver and co-driver "hoods" act as weak point and shot trap
M4A6 75mm unique in that it utilized a 51 degree, 2-inch thick glacis, without "hoods"

Late Production - all 75mm and 76mm with wet stowage except the M4A3E2
M4, M4A3 105mm rolled glacis at 47 degrees, 2.5-inches thick, "hoods" eliminated
M4A1 76mm cast hull, much improved quality control in casting, 2.5-inches thick, still 37-55 degrees but "hoods" eliminated
M4A2, M4A3 76mm rolled glacis at 47 degrees, 2.5-inches thick, "hoods" eliminated
M4A3 75mm rolled glacis at 47 degrees, 2.5-inches thick, "hoods" eliminated (Fisher M4A3)

Fisher also built M10 and M36, Ford built M10, Pressed Steel built M7 SP artillery. 1943/44 lines shut down
September 1943- Ford, Lima, Pullman
November 1943 - Pacific Car
December 1943 - American Loco, Federal Machine & Welder, Montreal
January 1944 - Baldwin

Before reallocating factory space to a new tank design there was a big requirement for locomotives and rolling stock to support Operation Overlord. By the end of June 1944 some
1,720 out of the expected requirements of 3,404 locomotives for continental operations (2,270 for the US forces) had arrived in England. In addition to the locomotives the US had sent 20,351 rail cars to the UK by 31st May 1944 for continental operations, of which 7,106 had been assembled. It was expected the allies would have to provide some 57,000 rail cars for continental operations.

The Canadians were building 25 pounder SP artillery chassis starting in April 1943. The 6 pounder Ram program ended in August 1942, Valentine program in May 1943.

marathag said:

German Engine compartment was pretty filled up, some pics grabbed from web search of a model
View attachment 822894View attachment 822895

Maybach and the Radial would be fairly similar in length, and while wider, doesn't need all that liquid cooled radiators and plumbing

I'm not seeing easy spark plug access here.

Rear Doors?
Easy.
Relocate the exhaust a bit, and borrow this from the sd.kfz 251
View attachment 822896
and then borrow the US idea for sliding out the engine like with the M-18 on rails
View attachment 822897

While the Germans had issues making enough BMW radials, They could use the Gnome-Rhone 14N twin row engines, a bit longer, and narrower and shorter, from the captured factories in occupied France.

Much more displacement, so will still run on lower octane gasoline than 87 if the C/R is dropped a bit.

Click to expand...

The German penchant for torsion bar suspension took up a lot of hull space.

I will note that for the US alone the plant (factories/tooling and such) surface engines (not air) a chart from Automotive Ind, Vol 82, No. 5, March 1 1940 shows a list of 483 different Stock, Marine, and Commercial Vehicle engines. This also includes Industrial engines. Obviously in such a list a few models may have been over looked. These ranged from a 11 cu/in single cylinder to Stirling Viking, an 8 cylinder 3619 cu/in engine that weighed 7100lbs used in Fishing boats?

None of the these engines were really suitable for tanks (power to weight and/or power to volume). I would also note that some of the big industrial/marine engine builders (size of engines) actually were not high volume manufacturers. Maybe a few dozen engines a month in a good month?

Perhaps somebody could make a tank specific radial using more steel and less aluminum and using less intensive machining. But you might as well start over on much of the engine design (keep bore and stroke?), which means you don't get to tool up right away.

Even some large companies didn't have the tooling needed for some of their own engines.
GMC was making a 707 cu/in six for Buses. Two spark plugs per cylinder and dual distributers. 175hp so a V-12 version might have been interesting.
But GMC capacity for build giant 6 cylinder engines for Buses and trucks was a lot smaller than their capacity to make small 6 cylinder truck engines or 6 cylinder car engines.

Admiral Beez said:

The German penchant for torsion bar suspension took up a lot of hull space.

Click to expand...

So did the Christi suspension. Torsion bars in the hull floor, Christi suspension in the hull walls.

Shortround6 said:

So did the Christi suspension. Torsion bars in the hull floor, Christi suspension in the hull walls.

Click to expand...

Bogies for the win... provided you can accept the limitations on ride and mobility.

Shortround6 said:

So did the Christi suspension. Torsion bars in the hull floor, Christi suspension in the hull walls.

Click to expand...

In fairness, you don't have to mount the Christi style springs inside the armored box. You can mount the springs in the space between the tracks, similar to the VVSS/HVSS that the Sherman used. Less volume that needs to be protected by armor and thus saving weight and width. OTOH, more easily damaged? For reference, Merkava suspension:

Everything has trade-offs.
The Christi suspension allowed for more wheel travel which allowed for higher speed. However even with Christi suspension the crew was still tossed around the inside of the tank in a rather dangerous fashion.
We also have to be careful comparing modern (1960s and later?) suspensions to older tanks.
Quality and design of springs and shock absorbers changed a lot in just 20 years.
A lot of WW II tanks were built cheap. Some did not have shock absorbers for each wheel/axel.
Some springs may have been progressive (resistance changes with amount of compression) but that is more expensive.
Modern tanks connect the suspension units together hydraulically. Swedish S tank was being developed in the 1950s (it took a while) but such suspensions can tilt the tank both fore and aft and side to side. Ride cross country improved a lot.

Basically if you don't have long travel suspension in the 1930s/40s you don't have a Christi suspension.


A short arm and a short spring means you have a short amount of actual travel.
The Soviets and British it was found that some of the travel was not actually useable. Cute picture aside the tanks never actually rode that smoothly and the tanks pitched and tossed, maybe not as bad as other tanks but at much lower speeds than advertised. Extreme wheel travel also tended to throw tracks which was huge pain in the butt and backs at best and fatal at worst.
What really sealed it's fate was size arms and springs you needed for 40 ton tanks.

Despite films showing extra fast Christie tanks racing across the screen on actual typical rough ground the speed differential to a bogie suspension was not that great. My Ukrainian ex Red Army tank commander found that his Valentine was usually as fast as a T34 in practice except on dry grazing land and kicked up less dust. His professional modus operandi was sneaky careful approach making maximum use of the tiny size and noise of the Valentine and not the ill trained conscript TC 'see enemy. Charge' which was about all the vision from a T34/76 allowed.