Category Archives: Turret

Post #70: Report on the New Weapons Board

Post #70: Report on the New Weapons Board

I downloaded this PDF, Report on The New Weapons Board 1944,  someplace, but since I don’t remember where I hosted it too.  The report documents the feedback the troops gave to the board on the various weapons they demonstrated.

The report was put together in early 44 to document feedback from the troops on current weapons, and proposed improvements, and replacements. There is a good amount of information on the M4 medium tank, and US Armor in general. Most of the combat feedback comes from the fighting in Italy, and North Africa.

The report also sheds an interesting light and gives evidence for the view that the US Army didn’t consider the improved early Sherman bad, and only wanted it replaced with something much better.  It also gives some interesting insight into the Shermans and what condition they were in when they got to the using units.

Feedback on current equipment and changes.

This is a typical M4 Sherman in Italy, the battalion is being used as an artillery battery, and this is an early production M4 with the M34 gun mount and it probably has a three-piece differential as well. It may even have DV ports. These tanks were common in the MTO even into 1944.

The first thing is this to note about the Sherman is the first mention of it is praise for the current models. This quote stands out, “No new type is desired unless the improvement in military characteristics is sufficient to warrant the changes and defects in the present standard tanks are avoided.” 

Another early model M4 in Italy, cheek armor, M34 gun mount, and an early 3 piece differential.

They did have a list of improvements they did want either done to the Sherman and to make sure the follow-on model, the T20 series incorporated them. 

  1. They wanted a 76mm gun like the 3-inch gun on the M10.  The news of the 76mm M1 series and the new Shermans mounting the gun interested the troops a lot. They brought an M4E6 76mm Sherman to show to the troops.
  2. Improved suspension and tracks. It turns out the rubber block tracks with no chevron were not well liked and wore out very quick in rocky, hilly terrain. The steel chevron blocks with rubber backs were well like and lasted much longer. This feedback is mostly from the MTO, the mountainous and rocky landscape was hard on tanks and even the Sherman had some issues. The complaints about the suspension had more to do with width than durability.
  3.   They wanted armored air cleaners on the M4 and M4A1 tanks.  It turns out the Air cleaners mounted under the overhang on the rear hull of the M4 and M4A1 tanks were prone to damage, and this damage was not expected and didn’t pick up until Italy so there was a shortage. All other models had the air cleaners inside the hull. Some units added improvised armor and some were added later in the production runs.
  4. Better ballistic angle around the front of the transmission housing.  The old three-part differential is what they are talking about. Most early Shermans had this type, and the armor was thinner than the later cast single piece units. There were two cast versions, an early thinner, but still no worse than the three-piece unit, and a later improved thicker one. There was a demand for add-on armor over this area, but it was never approved.
  5.  More power. Yet, when the M4A3 Ford GAA powered Shermans came online, they did not want to swap them in as replacements, and only wanted whole units who trained on them stateside first to be issued the improved tanks.  The M4A4 and M4A2 were not big enough improvements to switch to those motors. 
  6. Diesel engine. The US Army rejected the GM 6046, claiming it was not as reliable as the R975, but all the nations that did use this motor liked it.
  7.  They wanted better sights and fire control equipment. Many tanks in the MTO and NATO(North African Theater of Operation) had not gotten the M34A1 gun mounts with telescopic sights. The mount for the periscope sight had not seen major improvements, though there were field mods to make it work. The using arm was enthusiastic about the changes in the second gen Shermans fire control, but wanted even more advanced features, like rangefinders, and improved telescopes, since the current ones shot loose too!

There is also other tank related info.

  • The M3 75mm Gun –  Though well-liked for infantry support and deemed to be reliable and durable, the using arms almost universally felt the German 75mm PAK 40 guns were much better anti-tank weapons, and a high-velocity 76mm gun was in demand.
  • 75mm ammunition – these fixed rounds came unfixed, sometimes even in their travel packaging.  They wanted this fixed. They wanted the WP shells ballistics to match the ballistics of the common HE shell.
  • Large caliber cartridge cases – Steel cases for the 75mm rounds for the M3 gun were well received and proved more durable.  This was not the case for 105mm howitzer rounds.
  • 105mm howitzer armed tanks – This was not a popular notion because the M7 105mm GMC was inaccurate when used for direct fire to support infantry assaults.  The new weapons board did not agree, and plans for this vehicle were already in motion, and it would be well liked once issued.
  • Tank Officers – they wanted a tanker officer in the high-level headquarters to advise Division and higher level officers the best way to use tanks. AA and Tank destroyer officers were already an accepted part of these HQ staffs.
  • the 17-pdr gun – There was more interest in using this gun in M10s since the install was much simpler, the Sherman install was complicated and cramped and the Army was leary.
  • Tank Tracks – They show up again and the plain rubber block tracks could wear out in 250 miles in rocky terrain and lacked good off-road traction, and the using arm felt they were only good for training on roads.  The T54E1 steel chevron type was preferred and much more durable, but the T48 rubber chevron would work in the MTO but wore out faster than steel types. The T49 bar cleat was also not good on sidehill terrain. The using arm wanted a wider center guided track in the MTO because the side guided tracks on the Sherman were prone to throwing on irregular and rocky side slopes. Extended end connectors were well received by the using arms.
  • Tank Suspension – Sherman suspension was found to be durable, with few volute springs failing. The biggest problem was the bogie wheels since the rubber tires had an erratic failure rate, and unlike the spring failures, usually sidelined the tank.
  • Ammunition stowage – They using arms were not interested in changes that reduced the number of ready rounds. The turret ready racks were very popular and crews did not like their removal with the ‘quick fix’ mods. They were willing to risk the higher fire chance, for the faster rate of fire the early storage setup allowed. The crews did not get their way on this one, at least until the M26 went into production.
  • The Radios – They wanted a better radio in the M32 recovery vehicles and better, more comfortable headphones for the armor crews.
  • The M10 GMC – This TD was very popular, and received high praise all around. The using arm did not require a replacement, just improved M10s. ♠ One thing to note, most M10 GMCs in MTO lacked the Azimuth indicator and range quadrant. Since the M10s get used as artillery a lot in the MTO, they would like replacements to have them.

    M10 in Italy.
  • Replacement gun tubes – The using arms were very annoyed, that all type of gun barrels from machine gun and mortar, to tank and artillery, were dispensed at a very miserly rate.  The using arm argued replacement barrels should be bought at the rate that took into consideration how much ammunition for the same weapon was produced.
  • Improved fire control for all relevant vehicles –  They wanted built-in rangefinders, or portable ones supplied. Better periscope and telescope sights and all vehicles that could be used for indirect fire to receive the full suite of tools to perform the task.   I had never heard that some Shermans did not get these automatically. I’m not sure why some Shermans and TDs didn’t have the Azimuth indicator M19 and elevation quadrant M9. Maybe the crews dumped them to save space, maybe the tanks were rushed and built and approved without them I’ll try and find out. They mention 75% of the tanks in England had these items, but less 50% had them in the MTO.  Tank units were much more commonly used for indirect fire in the MTO than they would be in the ETO.
  • Engines –  The R975C-1 was getting around 200 hours before needing replacement. This was fine with the using arm, though they would like 60 to 100 more horsepower.  The R975 needed little maintenance to reach the expected 200 hours and many run much longer.  The lack of liquid cooling system has some advantages.
  • Powertrain –  There was a higher than expected rate of clutch failure in the desert campaigns. The clutch system was also improved on the production like with improved leverage to lower the clutch pedal pressure. Many MTO units did not receive the improved clutches or linkages.  The better clutches lead to better transmission life and better shifting, and even without the improved clutches, transmission life went up in Italy.  The powertrain offered excellent service and generally outlived the engines by several overhauls if not damaged.
  • Crew comfort – the Driver and Co-drivers seats in the Sherman were found to be ok, but higher seat backs were requested along with deeper seat cushions. The Gunners seat was found to be ok but could use the same improvements as the driver’s seats but the Command and Loaders seats were deemed all but useless. These would be improved in the later models of the Sherman and various TDs.  Crews do not use their seatbelts, fearing it complicating bailing out, and more padding inside was not wanted because the crews felt it was a fire hazard.  The M4 and M4A1 tanks were praised for good ventilation. There was also some discussion about the value of turret baskets, and if they were needed at all.
  • Ammo Storage – The early Sherman ready racks in the turret were well liked by the using arms, but they felt the sponson and hull ammo racks were no good and didn’t support the 75mm Shells enough. They would often separate and dump a bunch of gunpowder inside the tank making a deadly mess to clean.  The using arm tends to stuff the tank with extra rounds, adding to the shell durability problems. These problems would be addressed in the second gen improved hull tanks.
  • General storage – The current storage space on the Sherman was deemed ok, but better, easier to access bins were requested. They also wanted any storage in the floor to be resistant to getting filled with dirt or water.
  • Machine guns – The bow machine gun saw a lot of use, but its usefulness would be improved by a sighting system. One was in the works, but not at the point of this report.  The M1919 machine guns, both bow, and co-ax were reliable as long as the crew was careful with the ammo. Long road trips could vibrate rounds loose in the belts and cause problems, but under normal conditions, this was rarely a problem with well-trained crews.  The crews wanted a better adjustment method for matching the co-ax gun to the gunner’s site, the current one was not very good.  The .50 AA mount was not well liked or considered important. Requests were made for a better mount for ground targets.
  • Turret hatches – The current split hatch was deemed ok, but the crews like the looks of the new all around cupola and were also enthusiastic about a loader’s hatch on the new 76 armed tanks.
  • Armor – There does not seem to be a consensus on how much armor a tank should have by the using arms.  Armored Force troops felt the current level on the Sherman was fine, but wouldn’t mind more as long as it did not negatively affect flotation, maneuverability, and speed. ♠The British generally wanted heavier armor than the US Army.    ♠♠Combat in Italy showed the differential was taking more hits than anything, and another request was made for add-on armor for the area.
  • Sand Shields – The general consensus on these was they were useless in any theatre and needed to be redesigned. They needed to be easier to install, and designed to not trap mud.
  • Flotation – The using arms wanting tanks around 10 pounds per square inch. This was very optimistic since even the HVSS Shermans came in around 11 PSI, the basic 75 VVSS Sherman around 13.  It seems the Germans flooded fields in Sicily and Italy when they retreated, and Shermans got bogged down most of the time.  They offered the suggestion of just stretching the Sherman since more length would help, and the British M4A4 tanks, the longest production Shermans, had no maneuverability issues.
  • Maneuverability –   In the US Army there was a desire across the board for more maneuverability, in tanks. One thing to keep in mind though is the tanks in the MTO were older and most had single anchor steering brakes, the double anchor made the tanks easier to maneuver requiring less lever pressure. The ability to skid turn was not something US troops seemed interested in.
  • Accessories – The troops had a lot of feedback here. ♠ The instruments and gauges in medium tanks were not good quality, if they worked they didn’t work long. Oil pressure gauges fail, and no one worries about the motor until both oil pressure gauges die and a low oil pressure light comes on. This seems to be US feedback, I don’t recall hearing complaints from the Brits about Gauge quality. I wonder if the different tank plants sourced gauges from different companies. ♠♠ The compasses on US tanks would not stay calibrated. This would be a very annoying problem but eventually solved on second gen Shermans. ♠♠♠ Armor for the air cleaners on the M4 and M4A1 comes up again. ♠♠♠♠ The Auxiliary giving good service, and are well liked, but the using arms would like the area around the fuel tank filler for the Aux motor to be waterproofed better.  They also noted replacements were hard to come by.
  • Modifications –  ♠ The jist on this one was, in many cases modifications can be seen by inspecting a vehicle, but in others, access panels or more might have to be removed to check. The using arms proposed a record imprinted on a brass plate, attached to the vehicle, listing all the modifications that had been applied. ♠♠ They also wanted to emphasize that they did not want any modifications that would not ‘materially increase  the efficiency of the vehicles’
  • Development – The using arms were curious about the items in development, and finding out a large organization was working to improve almost everything was a morale booster. There was also interest in the T-20 series and if any test vehicles would be sent over for some for feedback like the M4A1 prototype has been.

 

Information and feedback on future equipment. 

  • The M4E6 or pre-production M4A1 76w –  ♠ This improved version was well liked by everyone who checked it out. The bigger turret was a big hit, though not much bigger, it seemed roomier. ♠♠ The improved fire control gear was very well liked and considered an ‘outstanding improvement’.  The 76mm gun was well liked, and everyone seemed to agree needed. ♠♠♠ The only real concern was the less effective HE round, but it was hoped they would make a better one.
  • The M18 76mm GMC –  The first and bad impression this vehicle lefts was it had no armor, and seemed very mechanically complicated.  The fire control gear was well liked. When the vehicle was demonstrated, the tracks and unthrowable tracks also got a lot of attention.  No one was sure if the speed would be useful, but the maneuverability was well liked. ♠ The same story with interest in deployment, not as a replacement vehicle, but fulling trained units from the ZI would be ok. ♠♠ This vehicle was not wanted by M10 units already deployed. Units equipped with it in the ZI then deployed were better received, the M10 was still more popular.  An M10 with a 90mm gun was the preferred replacement.
  • M4A3 75W – Even though the Ford GAA was a big improvement, it was not enough of an improvement to take them on as replacement vehicles. They were fine for them to be brought with units already fully trained on them.
  •  The M1 Dozer blade kit – This kit was an instant hit and would have many uses, including clearing rubble after heavy artillery reduced a strong point.  Currently, this has to be done by an unarmored bulldozer and casualties were high.  it was hoped they would work well enough to help tanks dig in or SPG prepare a position.  ♠ Through testing, they found this kit could be installed on any Sherman tank type.

This report goes into detail in the appendixes listing all the items demonstrated, and where they were demonstrated. They also include data on how many of the various items demonstrated were ordered by the various theatres.

I think it’s pretty clear the MTO was a backwater. The general shortage of spare parts in the MTO and a shortage of personnel to staff the proper echelons of repair and salvage system are also indicators of this. As they got ready for the June of 44 landings, the troops in England would be getting top priority and supplies and spares.

There is a lot of info on other weapons like artillery and small arms, not directly Sherman related and therefore, uncovered here. The report is definitely worth a download and re through.  I think it offers a good insight into the thinking involved on not swapping to 76mm armed Shermans before the Normandy landings.

 

# 15 Turrets: They Are The Combat Power Of The Tank

 

Turrets: They Rotate, and have Guns

Cute puppies!
Marine Cleaning his Tommy gun on a Late model M4A3 75 Sherman. Note the all-around vision cupola with periscopes mounded in the center of the hatch.

The Sherman had two turret types the 75mm turret and the later T23 turret with the M1 series of 76mm guns. The Jumbo had an up-armored version of the T23 turret.

split hatch details

One of the things that really set the Sherman apart from its peers, and gave it very good longevity, was the size of the turret ring. The Shermans were 69 inches, positively huge for when it was designed, the early T-34 had a 56-inch ring, and the later version with 85mm gun had a 63-inch turret ring. Nazi Germans are not very good in this area, PIII having a 60-inch ring, PIV having only 63 inches, and the Panther only having a 65-inch ring. Even the Tiger wasn’t huge, at only 70 inches! So what makes the size of the ring important? It is one of several factors that determine the maximum size gun you can mount on the tank. The other factors are the mechanical reliability of the vehicle and its load capacity, and how good the country building the tank was at making recoil absorption systems for the guns. The combination of automotive reliability, load capacity, turret ring diameter, and turret size allowed the Sherman to be up-gunned for decades. These factors were far more important than armor thickness when it came to the Shermans longevity. That the Sherman received more powerful guns than the Panther had, or could have had, is just one more reason why the Sherman was such a great tank, and better than the Panther.

turret collector ring
The turret collector ring allowed the turret wiring to go into the hull and still allow 360-degree traverse and not tangle any wires. All Shermans had essentially the same one.

Now let’s talk about turret drive motors.  There were three types used on the 75mm Shermans.

Oilgear: All models of Sherman tank had both powered and manual turret traverse. They did try various brands and types though. The preferred on the early Shermans was the hydraulic mechanism made by Oilgear Company. The Oilgear unit was both more precise because it had veritable sensitivity and more robust since it was able to keep the turret spinning even with minor flaws in the race or ring gear, than the other choices. Oilgear could not keep up with all the factories producing Shermans, so they had to go to other companies.

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The Oilgear traverse system and gunners station in an M4A2 76 HVSS tank
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The Oilgear Traverse System, and foot pedal triggers, and elevation wheel in a restored M4A2 76w HVSS tank

The Oilgear unit was hydraulic but powered by its own electric motor that spun a hydraulic pump and turbine setup to rotate the turret. The whole assembly was small enough to be mounted to the side of the turret, with a fair amount of room for the gunner.

Logansport: This Turret drive was very similar to the Oilgear unit, just not as precise, nor as good at dealing with imperfections in the turret race or ring. This unit was so similar the electric motor powering the hydraulic pump and turbine used the same reduction gears as the Oilgear unit.

The Logansport unit used the same mounting bracket as the Oilgear unit as well. The sensitivity to problems with the tolerances on the turret ring would make this drive more likely to fail from minor damage that the Oilgear unit would shrug off.

Westinghouse: The Westinghouse unit was just a big electric motor hooked to reduction gears. Since the motor ran at a faster speed, it had to be adapted to the stabilizer system but was still able to fit the same space and use all the mounting brackets of the other systems.

M4A4 Armament diagram westinghouse traverse 75mm early turret
Westinghouse traverse controls

The Westinghouse unit had the same problem with minor flaws in the race or sensitive to tightness in the ring gear.

Now, this would be a quality assurance problem at the factory in most cases. IE, when the tank got to the end of the line, and the QA inspector rotated the turret, and it screeched and slowed down over 10 degrees of rotation, it would be rejected, and sent to the factory’s QA shop to be fixed.  Battle damage might have caused some problems as well, but if the tank took enough of a hit to damage the teeth on the ring, or gear, it was probably going to be knocked out, and in really bad shape. That speculation based on how well many turret rings held up after years on firing ranges when the wreck they were in was restored into a beautiful working tank.

On the later T23 turrets, the Oilgear system was used for traverse control and an improved Westinghouse stabilizer was used as well.

The Westinghouse stabilizer: All models of the Sherman but the 105 armed tanks had a stabilizer to control the main guns in elevation while on the move. It used a gyroscope and hydraulic power pulled from the turret drive system to keep the gun steady in the vertical while on the movie. The system is often disregarded as an advantage by detractors, for a few reasons, but none are valid in a technical sense. The stabilizer was a very advanced piece of kit, and something the Germans could not copy, and never installed a similar system on a wartime tank. That it was complicated and the crews lacked training in using it, doesn’t mean it didn’t work and offer advantages to crews who bothered with it.

The original stabilizer was a little complicated to set up properly since many armor units received their tanks and maybe some manuals for them, when they formed, they often did not have a single man in their company who really knew how to make the stabilizer really work. This lead to it being turned off by a lot of early war crews. The wrongheaded belief the equipment was useless followed that. The Army did a test on it and found the stabilizer, when set up, and used by a crew who knew how to use it, it helped a great deal in getting off a fast first shot when the tank came to stop to shoot.  If the tank rocked, the gun stayed more or less on target. This was a big advantage to getting that all important first shot/hit in combat.

The Westinghouse stabilizer was improved and simplified in the second generation Shermans, the large hatch 75 and 76 tanks would have gotten it.  It was easier to setup and maintain, and the Army worked on getting crews trained on it.

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M3 2 inch Mortar

The M3 2 inch Smoke Mortar:  The M3, 2-inch smoke mortar was installed in the turret, with the muzzle opening on the forward left of the turret, on both the 75mm and 76mm gun turrets.  It was added to the tank at the request of the British and was loaded and fired by the loader. The mortar was loaded from inside, but protruded into the loaders space, and was not well liked. It could only be aimed by rotating the turret, and not all late model 75mm and 76mm turrets got them. Postwar, most were removed and the hole welded over.

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An M4 Composite hull, probably in the Philippines, with a good shot of the late model, split commanders hatch

The Hatches:  The Sherman’s turret started off with a single large split commander’s hatch. This hatch incorporated the m2 .50 HMG mount and rotated. It also had a standard periscope mounted on one side of the split hatches. This hatch went through several changes through its long life. Initially, the split commander hatch just depended on the weight of the armored hatch cover halves to hold them in the 45-degree angle position that sat in when open. They could be knocked loose when the tank was moving over rough terrain, and really hurt the commander.  They added a pair of hatch locks at the factory and fixed them in the field with kits. The final version of the split hatch had internal springs in the hinges to hold them open. There was also a version with a defect that passed factory inspection that showed up on some M4A1 76W tanks, where the split loaders hatch, essentially the same hatch that had been the commander’s hatch, was used for the loader, .50 M2 mount and all.  This was fixed pretty quick though, and then the hatch was replaced by the oval loaders hatch.

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In this massive image of an M4A1 76w tank, that has been modified with a flamethrower, after being repaired, note it has the split loaders hatch with the flaw that won’t let them open all the way.

When the second generation Shermans with the T23 turrets went into production, they all got much improved all-around vision cupolas. There must have been a shortage of contractors who could make it, because it was in short enough supply, the second gen large hatch, M4A2 75s, M4 Composite hulls, and M4 (105) tanks were all built with the original split commanders hatch.  The all-around vision cupola production was reserved for tanks armed with the M1A1 gun.  The cupola offered very good all around vision, with six armored glass viewing blocks, that were all replaceable, and a larger periscope mounted in a rotating center section of the hatch door. Towards the end of the war, the new cupola became more available and was fitted to some of the ultimate production M4A1 75, M4A3 75w tanks, and M4A3 (105) tanks.

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in this nice photo of an early production M4A1 76w Tank with the split loaders hatch. It’s also a pretty good shot of the all-around vision cupola

The oval Loaders hatch: The version of this hatch on 75mm turrets looked the same but was slightly smaller than the one used on the T23 turrets. The hatch was a spring-loaded oval hatch, either just big enough to get through or, big enough to get through comfortably, in the T23 versions. On the T23 turrets, when the oval hatch was installed, a new fully rotating periscope foreword of the hatch replaced the one that was mounted in the old split hatch.

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Soviet M4A2 76W tanks with oval loaders hatch.
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A late production M4A2 75 with a large hatch hull, oval loader’s hatch, on what is probably a high bustle turret, with a split commanders hatch.

. . .

Now for a final bit of information on the turrets and the stuff mounted on them. Over time the turrets picked up an external vane sight the commander could use to roughly put the gunner on a target, it looked like a whale fin in front of the commanders hatch on older 75mm Shermans. This was refined into a more useful, and less odd looking site that could be used from inside or out of the turret.  The .50 caliber machine gun mount started on the commander’s hatch, eventually moved to the loaders hatch, and then to the middle between the two hatches.  There was also a spotlight mount added, and it ended up being on late 75mm turrets, the T23 76mm turrets and even retrofitted to older 75mm Shermans.  The mount had an armored plug, the spotlight plugged into, and could be controlled from inside the tank, much like the spotlights you see mounted to the side of police cars. The turrets also started out with no brackets for storing the heavy machine gun, but they started showing up on 75mm turrets and were on almost all T23 turrets.  Even where the lifting eyes were moved around on the turrets.

♠♠♠

From looking at period pictures, it was very common for the gunner or loader to ride standing in the commander’s hatch, while he was in it as well, the split hatch cupolas were that big. I thought I wouldn’t see the practice on tanks with the all-around vision cupola, but I found a few were the crews did it there too.

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This Marine M4A1 in the jungles of Cape Gloucester has its commanders hatch being shared by two crewmen

 

Riflemen of the 29th Marine Regiment ride a M4A3 Sherman 105mm of Company A, 6th Tank Battalion during the 6th Marine Division's drive on Chuda along the west coast of Okinawa. After expecting a contested landing on April 1, 1945, and seeing little of the Japanese, the Americans were in high spirits as objectives are taken ahead of schedule in Northern Okinawa; the Shuri Line would rob them of their high morale. The 29th Marines cut off the Motobu Peninsula and seized Chuda at 1200 Hours on April 6, 1945. Tank-infantry teams encountered sporadic resistance during the initial invasion; most problems were from the Japanese blowing bridges as they retreated inland. Destruction of bridges had been inept; frequently only a span of the bridge had been blown or cracked. The engineers cut quick bypasses for the vehicles, repairing the broken spans later. 500 M4A3 Shermans with the M4 105mm gun were built in late 1944. Later versions of the 105mm Sherman had a more advanced horizontal volute spring suspension (HVSS) with wider tracks that allowed for a smoother ride. Note partially dismantled deep wading gear to allow the M4A3 to move through deep water during the landings a few days before. The M4A3 Sherman with the M4 105mm howitzer was not popular with the tankers, who preferred the M1 76mm high-velocity gun in case of tank-against-tank engagements. However, the 105mm-equipped Shermans were very popular with ground troops, who used tanks as mobile pillboxes, taking out Japanese positions with point-blank high explosive fire.
On this M4A3 105 in Marine Service, you can clearly see the commander and probably gunner sharing the all-around vision cupola!
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An Army M4A3 75 tank with a split commanders hatch, oval loaders hatch, and the commander and gunner sharing the split commanders hatch, somewhere in the Philippines.

. . .

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An M4A4 that has been modified to take a different motor, with a mid-production 75mm turret, with split commanders hatch, and a welded up pistol port. It also has the stubby mantlet, and you can just make out the original commanders vain sight in front of his hatch

 

The standard 75mm Turret:  The Sherman’s First Turret, It Had Many Minor Changes

The standard 75mm turret started out with a stubby rotor shield that just covered the base of the 75mm gun. These early turrets didn’t have a direct telescopic sight for the gunner either. The gunner had to rely on the M4 periscope to aim the gun. The turret had one large hatch for the whole turret crew to get in and out from and a pistol port on the loader’s side that could be propped open and spent 75mm shells dumped out.  The loader and commander had fully rotating periscopes to view the world through, the commander’s periscope was in his hatch, the loaders right above his station, and the middle of the turret roof had an armored ventilator. Many of these turrets had a weak spot in the armor due to an area machined to fit the turret drive. This area was covered with additional armor on once the problem was discovered.

207786550-2 M4 wrecking yard
In this shot of a Sherman wrecking yard in Europe, you can see the early 75mm turret with depot or even factory level rebuilds, on these tanks before they were knocked out. They could be M4s or M4A3 tanks that were used in the US for training and refurbished on shipped to the ETO. You can see the split commanders hatch, though missing the hatch doors on two of them, the full-length gun mantlet, the welded on cheek armor over the weak spot and the commander’s old style vane site.

The small rotor shield and lack of telescopic sight were some of the first production line changes, and older tanks were field modified with kits to update them, often only covering half the turret with added armor on the mantlet to protect the new telescopic site. The new factory full-size rotor shield covered the majority of the turret face with much thicker armor. The next big change was a weak spot in the right side of the casting where a thin spot was made while machining the turret for the gun mount was discovered, and armor was welded on the outside of the turret to thicken it back up. Tanks were retrofitted with this armor in the field, and later the casting was changed to include the thicker armor over the area, eliminating the need for the welded on cheek armor.

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This M4 Composite hull tank in the Philippines has the split style commanders hatch on a 75mm turret with most updates

At some point, while all the above was going on someone decided the pistol port was a weak spot and it had to go. So they started welding them closed at the factory, and then the casting had them removed. Then the men in the field went ape poop, and they put it back in, around the time the ultimate 75mm turret went into production, with the thicker armor cast in, the pistol port back, a new all-around vision cupola for the commander and an oval hatch for the gunner.  This would be the final configuration of the 75mm turret. The tolerances used by US tank factories were close enough turrets cast at one factory could be used at another with no modifications. Many older surplus turrets left over from the tank retriever conversion program were used in later production, with all the updates added, and a hatch cut in for the loader. Due to a shortage of all-around vision cupolas, many 75mm turrets with a loaders hatch ended up with the old split style commander’s hatch.

pistolport inside

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This M4 has split commanders hatch, commanders vane sight, full gun mantlet, and welded up pistol port

When hull production switched over to the 47-degree frontal armor configuration, and they went with the large driver and loaders hatches on the M4, M4A2 and M4A3 production, the 75mm turrets needed modification. The hinge for the larger drivers and co-drivers hatches stuck up higher than the older small hatch hulls, they could interfere with the turret’s rotation, since they barely cleared the bustle was the radio was mounted in the back of the turret. The first solution was to notch the bustle a little, but they also changed the turret casting, raising the whole bustle area and making the top of the turret flatter.

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Chopper is an M4A3 75 W tank, used by the Marines on Okinawa

The turret drive motor was either an electric motor driven hydraulic system or a straight electric motor driven system. The hydraulic system was the preferred, but when that system was in short supply the electric system was substituted.  The 75mm turret could rotate 360 degrees in 15 seconds with the power traverse. It had a manual traverse system as well, and elevation was handled through a manual wheel.

For the very best in minute detail on this subject, please check out the Sherman Minutia site. One minor bit of trivia about the original style turret, the D50878, and D78461 castings, the ones produced for the 105 armed tanks were unique, in that they had an extra armored ventilator whole drilled in so another one could be mounted. So the 105mm turrets really are 105mm only. I’m still not sure if there is a 1/35mm Sherman M4 105, or M4A3 105 with the correct turret.

 

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An early T23 turret on an M4A1 76w tank. Not all around vision cupola for the commander and the split loaders hatch

The T23 Turret: Developed For the Failed T23 program, It Found a New Purpose on The Sherman

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The origin of the T23 turret, the fascinating T23 medium tank. It used a gas generator powered electric drive system, but unlike the ones the Germans used on the Elephant, it worked.

While the 75mm turret was still in production and being improved, the T23 turret, taken from the failed T23 medium tank project, went onto the Sherman with the M1A1 gun on the big hatch, wet ammo rack hulls. This turret was larger and could fit the 76mm gun with much more comfort than the basic 75mm turret. All T23 turrets had loaders hatches, though early production T23 turrets used the hatch that had been the commanders hatch on older Shermans for the loaders hatch and used the new all-around vision cupola for the commander. This didn’t last long; it was found the narrow area between the two large hatches on the roof was a weak spot. The big loader’s hatch went away and an oval hatch went in.  These turrets had the same traverse speed as the 75mm turret and the same ROF.

Division-Photos
Pn this M4A1 76w tank you can see the commander in the all-around vision cupola, and the split loaders hatch open

The T23 turret came in around 4000 pounds heavier than the 75mm turret. The automotive systems of the Sherman tank were strong enough to support the extra weight without any real change in performance or longevity. The drivetrain didn’t receive any changes at all as far as I can tell, and only the Jumbo tanks got a different gear ratio in the differential. All the extra weight in sandbags, concrete and real armor did shorten the life of the automotive components but not by a significant amount.

All T23 turreted 76mm gun tanks, had wet ammunition storage, as did the Jumbo tanks, but not all large hatch hulls did. The M4 (105), M4 composites, and M4A2 large hatch 75mm tanks all had dry ammo racks.  The T23 Turret would get the smoke mortar, and an extra periscope hole machined in when the split loaders hatch was replaced with the oval hatch.

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T23 turret on an M4A3 with the 14th AD
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Another M4A3 76 tank with T23 turret serving with the 14th AD

Sources: Armored Thunderbolt by Zaloga,  Sherman by Hunnicutt, Ballistics and Gunnery by Bird and Livingston, The Sherman Minutia Site, Son of a Sherman by Stansell and Laughlin, M4 Sherman tank at war by Green, Tanks are a Might Fine Thing by Stout, the Lone Sentry, TM9-731B M4A2, TM9-731G M10A1, TM9-745 GMC M36B2, TM9-748 GMC M36B1, TM9-750M3, TM9-752 M4A3, TM9-754 M4A4, TM9-759 M4A3,  FM17-12 Tank Gunnery, FM17-15 Combat Practice firing, FM17-67 Crew Drill and Service of the Piece M4 Series