United States of America (1941)
Medium Tank – 1,000 Planned, 12 Built
As early as summer 1941, it was outlined in the design of the Medium Tank T6 – the future M4 Sherman – that consideration be given to a degree of modularity when it came to the tank’s main gun. It was hoped that the standard 75 mm M3 Gun, the 3-inch (76mm) Anti-Tank Gun, and the 105 mm Howitzer would all fit in the same turret. While the 3-inch gun was already slated as the main armament of the ill-fated M6 Heavy Tank, it was found that it was too heavy for the Sherman’s smaller turret. What was needed was a gun with the same performance as the 3-inch that could fit in the 75 mm mount without affecting the turret.
The culmination of this program was the Medium Tank M4A1 (76M1), a true example of the old adage that “an inventor’s dream is a soldier’s nightmare”, and a highlight of the inter-departmental politics that can affect tank and armored vehicle design. Namely, in the case of the 76M1, while the designers accepted the design for service, the ‘top brass’ of the tank force it was designed for did not. As such, getting a 76 mm gun into the M4 became a far more convoluted process…
Disclaimer: The ’76M1′ that identifies this particular model of the M4 comes with a caveat. Although not appearing to be present in any official paperwork, numerous secondary publications use this identifier, starting with R.P. Hunnicutt’s Sherman: A History of the American Medium Tank published in 1978. Publications since that time also frequently use the term. ’76M1′ is used in this article to differentiate the tank from other 76 mm-armed M4s.
Mythbusting
The first thing to cover are the various myths surrounding the choice of main armament for the M4 tank. It is often claimed that, as it was not designed as a ‘tank destroyer’, the M4 was not intended to be able to fight other tanks, with precedence given first to the task of infantry support via high-explosive (HE) shells. In a lot of cases, the 75mm was prefered due to the available HE round. It was more likely that US forces would run into infantry anti-tank weapons rather than armor itself, and HE dealt with this better. It is further claimed that the 76 mm was only developed as a knee-jerk reaction to the emergence of the heavy German Panzers, and the US took too long or was not proactive enough in giving greater firepower to its armor. None of these claims are true.
Simply put, the US was mounting the most potent gun available at the time that would fit inside the M4’s turret while keeping it balanced. At the start of the war, this was the 75 mm Tank Gun M3. It had nothing to do with tank destroyer doctrine or the prioritization of HE. Further, the tank destroyer doctrine had to do with larger armored units, where tank destroyer battalions would have the duty of countering larger enemy armored units. If an M4 Sherman unit encountered enemy tanks, it was not supposed to withdraw or ignore it, but it would engage it. Also, the development of fitting a 76 mm gun on the Sherman pre-dates the US Military’s first encounters with tanks such as the Tiger I or Panther. Second to this, when the 76 mm became available, greater anti-tank firepower was sought specifically in order to take on enemy armor. The military was also clearly not passive when you consider that the 76 mm was installed partially for the reason of ‘just in case heavier tanks show up’.
It is all very well looking at history with the benefit of hindsight, but one must remember the nuances of tank design, military doctrine, industrial limitations and logistics and look through the lens of the era in question.
Base: Medium Tank M4A1
The M4 series of tanks is undoubtedly one of the most recognized to come out of the Second World War. Starting life in 1941 as the T6, it was later serialized as the M4. The British named it ‘Sherman’ after William T. Sherman, General of the Union Army in the American Civil War. The tank officially entered service in 1942 and saw its first action at the Second Battle of El Alamein that October with the British 8th Army.
The M4A1 was the second variant of the M4 Sherman, easily identifiable by its bulbous cast hull. The Pressed Steel Car Company (PSC), Pacific Car & Foundry, Lima Locomotive Works, and Montreal Locomotive Works (MLW) produced this model. MLW-produced tanks were the ‘Grizzly’ variant. The M4A1 was armed with the standard 75mm Tank Gun M3, as well as a multitude of machine guns.
The powerplant of the M4A1 consisted of the inconveniently large Continental Radial engine, rated at 350 to 400 hp. It had to be mounted vertically in the tank, resulting in the characteristically deep hull of the M4s. The average speed of the M4 series was 22–30 mph (35–48 km/h). Overall weight was about 33 ½ tons (34 tonnes), supported on a Vertical Volute Spring Suspension (VVSS), with three bogies on each side of the vehicle and two wheels per bogie.
Square Peg, Round Hole
The idea of modular weaponry was relatively forward thinking in 1941. For the T6, the idea was to use replaceable turret face-plates, making switching extremely quick and easy. As well as the 75 mm M3 and 105 mm M4, it was hoped that a 3-inch gun would also fit. Getting the 3-inch gun onto the M4 chassis was never an easy task. The 3-in gun was designed first as a towed gun, and it proved difficult to mount on a vehicle due to its length and weight. Previous experiments with the Gun Motor Carriages (GMCs) T40 and T57 had the gun in a casemate style mounting, but neither were successful.
It was found that the 3-in gun could be mounted on the M4 chassis, if installed in a simplified open-top turret with no coaxial machine gun. This would become the tank destroyer Gun Motor Carriage M10 Wolverine. An expedient design, the M10 was unnecessarily heavy, due to the need for vast counter weights on the turret rear to balance the turret. This is a problem that would be exacerbated when considering a tank mounting, the armor of the turret face and coaxial machine gun would also have to be accounted for. Further development of a 3-inch gun suitable for tank mounting resulted in the 3-in Tank Gun M7. This 76 mm-bore gun was slated as the main armament of the ill-fated M6 Heavy Tank. It was a far-better tank-killing gun than the lower velocity 75 mm, however, the problem was that it was much too heavy for the T6 Medium’s turret.
A new program was initiated to develop the T1 76 mm gun, a weapon that would ideally have the power of the M7, but fit in the standard M34 gun mount used for the 75 mm M3 gun. For ease of development, the same projectile as the 3-inch M7 would be used but with an adapted propellant case and charge, while still achieving a muzzle velocity of 2,600 fps (792 m/s). The gun was made to be much lighter than the original 3-inch gun, but was longer, at 57 calibers (14 ¼ feet/4.34 m) compared to the original 50 calibers (12 ½ feet/3.81 m). T1 was fitted with the same breech ring as the 75 mm M3, and was able to fit in the standard M34 gun mount.
Two T1 guns were produced and sent for testing at Aberdeen Proving Grounds (APG), Maryland, in August 1942. One was placed in a fixed test mount, while the other was installed in an M34 gun mount and in the turret of an early model M4A1. In the M34 mount, it was found the gun was terribly unbalanced and drooped rather drastically. This was remedied quite quickly by chopping 15 inches (38 cm) off the muzzle end of the gun (bringing the bore length to ~13 feet/4 m), and adding weights to the breech end. With these modifications made, the gun performed well. Firing the standard Armor-Piercing, Capped (APC) round, the 76 mm gun could punch through 4.3 inches (109 mm) of armor at 0° obliquity at up to 3,300 ft (1,000 m), with a muzzle velocity of 2,600 ft/s (792 m/s). Following these tests, APG recommended that the modifications be standardized, and declared the T1 gun satisfactory for service on the M4 series.
On August 17th, Following the initially positive tests, the Ordnance Committee recommended that M4s equipped with the 76 mm were to be designated as a Substitute Standard (limited production variant), and the gun be serialized as the ‘76mm Tank Gun M1’. As such, tanks equipped with it would receive a designator in parentheses – ‘M4A1 (76M1)’ for example – authenticity notwithstanding. At this time in 1942, it was planned that 1,000 tanks would be produced with the 76 mm gun.
Testing continued at APG in October 1942 with the gun in a modified set up, installed in a later-model M4A1. The weapon was placed in the new Combination Gun Mount M34A1, which featured a much wider armored mantlet and came with enhanced gun-sighting in the form of the T60/M51 3-power direct-sight telescope. In this new mount (re-designated as M34A1E1 when modified to carry the 76 mm gun), the gun had a vertical traverse range of -12.5º to +25º. The standard .30 Cal. (7.62 mm) Browning M1919 was retained as the coaxial machine gun. Other modifications were introduced. A new front plate for the turret was also developed, incorporating a spacer that moved the gun forward approximately 2 inches (50 mm), granting more room around the breech end of the gun and preventing interference with access to the radio. Counterweights were added to the recoil guard to properly balance the gun to allow proper operation of the original gyro-stabilizer.
Coupled with the direct vision telescope, better accuracy was achieved over the original periscopic sight. Provision was made for the stowage of 83×76 mm shells. Once again, the results were initially positive, with officials finding the mount perfectly satisfactory for service. The use of T60/M51 3-power direct-sight telescope was also found to provide much better accuracy than the standard periscopic sight.
However, one issue still to overcome was the balancing of the gun. The long 76 mm made the turret drastically unbalanced, so much so that, on a 30º gradient, both the standard Oilgear and Westinghouse traverse gear struggled to provide rotation, although both did manage it eventually. It was suggested that an 800 lbs (>362 kg) counterweight be added to the back of the turret, with further suggestions that this could take the form of a stowage box. When the turret was retested with the additional weight, it was found that it suitably rebalanced the turret, allowing the existing gears to work.
Now officially serialized, the Pressed Steel Car Company produced 12 tanks for further tests at APG, and for evaluation by the Armored Force Board and the Tank Destroyer Board, which were ready by late 1942. A couple would also be sent to Fort Knox, Kentucky, in early 1943, and others would see field tests with the 7th Armored Division at the Desert Training Center in California. PSC produced the M4s with APG’s recommendations in mind, consisting of the larger, heavier turret bustle incorporated into the turret casting. Also, as well as the standard travel-lock on the upper glacis, another was installed on the engine deck. Service tests commenced, with a final report being filed in April 1943.
The Ordnance Branch was pleased with the arrangement, but the Armored Force, representing the personnel that would be expected to use the thing, were not happy with it at all. They claimed that the little amount of space left in the turret was simply impractical and that the project represented a poor quick-fix to allow for rapid production. With this disapproval from Armored Force, Ordnance Board quickly revoked the Substitute Standard classification, and canceled an order with Pressed Steel Car for a further 17 M4A1 (76M1)s. The project was canceled in May 1943, but APG, Ordnance Board, and Armored Force were each told to keep one 76M1 tank each. The remaining 9 tanks were to be converted back into standard 75 mm tanks.
Further Experiments
While itself not a success, the M4A1 (76M1) was the first step in getting better anti-tank firepower into the M4 Medium Tank. The Ordnance Branch’s cancellation of the M4A1 (76M1) program in May 1943 also marked the start of a new project with the same goal. Designated the M4E6, these tanks were to be equipped with the 76 mm gun mounted in a new larger turret initially designed for the T20 Medium tank program. It was also the first to trial a new ammunition stowage layout aiming at reducing ammunition cook-offs. Stowage was moved from the sponsons to the hull floor, placed in compartments surrounded by water. This became the standard ‘Wet stowage’, and any tank with this received the ‘W’ designator – M4 (75) W, for example.
The T23 turret, as it would come to be known, consisted of a larger casting with an open front through which the 76 mm gun would protrude. The opening was covered by a large gun-shield/mantlet that was 3 ½ inches thick. In this prototype, the gun used was the M1A1 variant, mounted in the Gun Mount T80 with standard coaxial machine gun accompaniment, and full vertical stabilization. The M1A1 gun had a longer recoil distance than the original M1, which required the gun to be mounted further forward on its trunnions, in turn allowing increased balance without the need to apply counterweights.
The larger turret granted much better internal space, making the mounting and operation of the 76 mm a far more comfortable task. The turret kept the original large, circular two-piece commander’s hatch, but a smaller hatch was added for the loader as well. Two M4E6s produced with one going to the Detroit Arsenal, with the other going to Aberdeen and then Fort Knox for trials. In August 1943, the Armored Force recommended that M4s of the E6 standard be put into immediate production, with the familiar initial order of 1,000 tanks. More cross-departmental disagreements then ensued. The Chief of the Ordnance was instructed to order the cessation of production of 75 mm guns, however the Armored Force did not want to completely phase out production of the 75 mm gun, as it had a better high-explosive shell.
It was not until further combat experience that the US Military realized that they did actually need more firepower. The idea of mounting the T23 turret on existing M4 hulls was revisited and serialized. Production of M4s with a combination of the T23 turret and M1 76 mm gun began in September 1943. Existing models, such as the M4A1 and M4A2, received such upgrades, but the development also coincided with the major redesign of the hull, a change in ammunition stowage, angle of the upper glacis, and increased crew-hatch size. All of these changes, as well as the T23 turret, were implemented on the newer M4A3. Any M4 equipped with 76 mm would receive the ‘76’ in parentheses, denoting it was a 76 mm gun-armed tank, M4A1 (76), for example. The first combat use of a 76 mm Sherman would not come until July 1944, with Operation Cobra.
Return to the Small Turret
Of course, the most famous attempt of getting a big gun into the small turret was the British Sherman IC and VC Firefly. The conversion of which wedged the 17-pounder anti-tank gun into the small turret. This vehicle would serve the Brits well from 1944 to the end of World War Two. The only reason it is not mentioned more in this article is that the 17-pounder is not an American 76mm gun. Back on topic, post-war, the US and other M4-equipped nations continued to explore the idea of getting the 76 mm into the original ‘small’ turret.
In the late-1940s, the idea of wedging the 76 mm M1 in the ‘small’ M4 turret was revisited in the name of international military aid, namely the Mutual Defense Assistance Program (MDAP). M4 tanks were effectively pieced together from stocks of spare parts, resulting in the M4A1E6 and M4A3E4. Both of these models featured the M1A1/M1A2 76 mm gun placed in the older ‘small’ turret in much the same fashion as the M4A1 (76M1). Wanting to keep the most up-to-date components for their own M4s, these foreign aid tanks never received the newer T23 turret or Horizontal Volute Spring Suspension (HVSS). The M4A3E4 would go on to see service in Denmark, Portugal, and Yugoslavia, while the M4A1A6 would serve in India and Pakistan.
With the Korean War in 1950, the Tokyo Ordnance Depot became a maintenance hub for the US Military in the region. In addition to repairing regular M4s, the Depot also began to refit older stocks of M4s, and up-gun M4A3 (75)Ws. In much the same fashion as the E6 and E4, this involved placing the 76 mm gun in the older turret. While visually similar to the other projects, it is unclear how exactly it was managed, how many were built, or whether they saw action.
Another similar up-gunning was done by the Italians. Between 1948 and the mid-1960s, the Italian Army operated M4s of various models. Around 1952, perhaps after seeing the MDAP M4s become available, the Italian military experimented with placing the 76 mm M1 on their ‘small’ turret M4A4s. This work was carried out by the Piacenza Arsenal, and, like the early M4A1 (76M1), the gun was placed in the original M34 mount. Not much is known about this conversion at present, but it would appear to have been a one off and was never mass-produced.
Conclusion
Although the Medium Tank M4A1 (76M1) was ultimately canceled, programs with similar goals continued. However, the task of getting the 76 mm tank gun to battle became a long one, fraught with cross-party disagreements and problems with making it serviceable. It was not until the employment of the T23 turret that the US military had a viable means of granting greater firepower to the Sherman. Armed with the 76 mm, the M4 would go on to serve through the rest of World War Two, and would also see action in the following Korean War, before being declared obsolete (as a gun tank) by the US in the late 1950s.
Illustrations by Ardhya ‘Vesp’ Anargha. These illustrations are sponsored by our Patreon Dave Shuford. Find out how to sponsor an illustration by becoming a Patreon.
Specifications |
|
| Dimensions (LWH) | 24ft 7in (without gun) x 9ft 8in x 9ft 7in (7.54 (without gun) x 2.99 x 2.97 m) |
| Total Weight | 33 tons (30 tonnes) |
| Crew | 5 – commander, gunner, loader, driver, bow-gunner |
| Propulsion | Continental R975, 9-cylinder radial, gasoline |
| Maximum Speed | 21 – 24 mph (34 – 39 km/h) |
| Suspension | Vertical Volute Spring Suspension (HVSS) |
| Armament | 76 mm Tank Gun M1 Coaxial and bow mounted .30 Cal. (7.62 mm) Browning M1919 machine guns |
| Armor | Hull front: 2 inches (50 mm) @ 37 – 55° Sides & Rear: 1 ½ inches (38 mm) Roof: ½ – ¾ inches (12.7 – 19 mm) Turret face: 3 inches (76 mm) @ 30° Mantlet: 3 ½ inches (88 mm) Sides & Rear: 2 inches (50 mm) Roof: 1 inch (25 mm) |
| Production | 12 |
Sources
R. P. Hunnicutt, Sherman: A History of the American Medium Tank, Presidio Press, 1978
R. P. Hunnicutt, Firepower: A History of the American Heavy Tank, Presidio Press, 1988
Patrick Stansell, Son of Sherman, Vol. 1, The Ampersand Group, 2013
Janusz Ledwoch, Sherman 76 mm, Tank Power Vol. CCV 470, 2019
Pierre-Olivier Buan, Joe DeMarco and Leife Hulbert, Sherman Minutia (1) (2)
The Chieftain’s Hatch
www.strijdbewijs.nl
US variants
W_11TB_10AD_Ardennes_HD.jpg "Sherman M4A1(76)W")
W_HVSS_HD.jpg "Sherman M4A1(76)W HVSS")
W_russian.png "Russian M4A2(75)W")
.png "Panzerkampfwagen M4-748(a)")
W_Russian_1_HD.jpg "M4A2(76)W")
W_late_Russian_HD.jpg "M4A2(76)W, late version")
W_HVSS_Germany45.png "M4A2(76)W HVSS")
w_HD.jpg)
