Authored By Dan Alex (Updated: 9/29/2016):
Europe Changes Everything
Events in Europe, following the German invasion of Poland on September 1st, 1939, necessitated a change to American tank design philosophy. To this point, America had put more emphasis on the development of light class tanks with only a smattering of resources going into medium tank development. The appearance of the German Panzerkampfwagen IV medium tanks running rampant across Polish defenses raised awareness on the part of the Americans, whose congress was still reluctant to release money to the military to upgrade their forces as Poland was, more or less, viewed as a less-than-capable military power of the time - the results were rather expected. However, that all changed once the French defenses suffered the same type of defeat. France was considered a major military power for the time and to see it dismantled by Germany's use of coordinated land and air power came as quite a shock across the world. Now with Paris under control of the Nazis, the US Congress had little reservations (or choice for that matter) in releasing millions of dollars in an effort to revamp the aged World War 1-era American armed forces.
The German Panzerkampfwagen IV (or simply Panzer IV) was originally intended as an infantry support tank. The presence of the mighty Soviet T-34 tank soon forced the Panzer IV to take on a "truer" tank-versus-tank battlefield role in which the Panzer could effectively engage the T-34's in head-to-head combat. The Panzer IV, therefore, was appropriately up-gunned and up-armored to meet this new Red challenge and went on to become the most produced tank in the German Panzer ranks. Such was the success of the Panzer IV that they were even fielded as late as the 1960's under the Syrian flag in the Six Day War - a true testament to the design's reach. The Panzer IV would go on to become the M4 Sherman's primary adversary across the North African and European fronts of World War 2.
The M3 Lee Medium Tank
The Americans designed the high-profile M3 Lee as an interim, this being based on the M2A1 Medium tank of which itself was an evolution of the M2 Light Tank. The M3 Lee was a serviceable tank system with very serious drawbacks in the way of off-road performance, a tall side profile and having her 75mm main gun mounted in a World War 1-style limited traverse "offset-right" sponson turret - the latter drawback limiting her ability to bring fire to bear on a target in time by forcing the entire tank system be turned to face the target. Though the M3 was limited in these factors, she was hardily available and her armor was sufficient. At the time, her 75mm armament finally gave the Allies a competent main gun for which to field against German armor in North Africa. She was first fielded by the British Army whom upheld their tradition of naming American-produced tanks after famous civil war generals (Robert E. Lee for the "M3 Lee" being the example here). The British were desperate to fill their dwindling supply of capable armor lost at the historical Evacuation at Dunkirk and in the grand desert campaigns of North Africa. The M3 would have to do for now.
The new design was put into action beginning on August 31st, 1940. This medium tank would have to mount a 75mm main gun armament into a full-traverse turret. The new tank would also have to incorporate the engine, transmission, tracks and suspension systems of the M3 Lee medium tanks in an effort to ease production and save time. This new medium tank would also have to reduce the crew from six to five and feature improved armor allocation without increasing the vehicles overall weight (it was seen that the tank would have to be able to pass over the old bridges and roadways of Europe and Africa for it to stay relevant in any offensive movement). Design was to commence once the M3 series was out the door and was placed at the feet of the Aberdeen Proving Grounds.
The design appeared as the T6 pilot model and proved acceptable to US Army officials and production was ordered for the new "M4" on September 5th, 1941. Before production on the M4 ramped up, however, the M4 design was further revised to include a 12.7mm heavy-barrel Browning machine gun on the turret for anti-aircraft defense. A .30 caliber machine gun was then added to the upper hull bow plate. Though an additional paired 2 x .30 caliber bow-mounted, driver-operated machine guns were requested, these weapon systems were eventually dropped from the final production M4 form. Initial Shermans were produced as two different designated marks with the M4 sporting a welded hull and the M4A1 sporting a cast hull. By the end of the Sherman production years, construction of the tank would be handled by a variety of American heavy industry companies that included the American Locomotive Company, Baldwin Locomotive Works, Detroit Tank Arsenal, Lima Locomotive Works, Pressed Steel Car Company, Pacific Car and Foundry Company and the Pullman Standard Car Company.
Like the M3 before it, external design of the M4 Sherman was characterized by its tall - albeit stout - profile. The Sherman was a large tank by any measure and featured an angled upper body fitted to an angled lower front hull. The most distinctive external marker for the M4 Sherman was her broad, sloped frontal hull armor with protruding position hatches for the driver and bow gunner. Wheels were similar to their original M2 design, sporting six road wheels to a side and fitted into three suspension bogies. The main gun (whatever the role was for a particular Sherman system) was fitted into a smooth and rounded turret encasement. Top hatches were provided for the driver, assistant driver and the tank commander (the latter's hatch in the turret while the loader received his own turret-mounted hatch in later Shermans). An emergency hatch was added to the hull floor just behind the bow gunner. Despite being shorter than her M3 sister, the M4 Sherman was still taller than her contemporaries like the Soviet T-34 and the German Panzerkampfwagen IV. Mounting the engine to the rear of the design was an accepted practice and continued to be so even on today's modern battlefield with the exception of the Israeli Merkava - this tank mounts her engine in the front, increasing the chance of crew survivability from a direct head-on hit. This design choice seemingly stemmed from Israel's previous - and multiple - armor campaigns against Arab nations leading to the assumption that Israeli tank engineers might know something the rest of the tank-designing world does not. The entire interior of the M4 Sherman series was painted in an overall white scheme.
The Sherman Crew
Crew accommodations amounted to five personnel (typical of the time in handling the various workloads aboard a conventional main battle tank) and consisted of the driver, the assistant driver/bow gunner, the ammunition loader, the gunner and the tank commander. The driver was situated at the forward left of the design. His position was dominated by two steering levers and floor pedals derectly ahead of his seat and an instrument panel situated to his immediate left. To his immediate right lay the transmission cover and a above that a storage shelf. The driver had free vision over to the bow gunners position to his far right and could visibly see the gunner, loader and commander behind him in the turret basket. The driver originally had access to a direct-vision slot but it was done away with in favor of a fixed periscope when the vision slots proved to be yet another ballistics weakness. The instrument panel contained basic performance gauges (speed, tachometer, oil pressure, fuel, etc.) as well as the starter switch, circuit breakers and two utility outlets.
The driver and bow gunner sat lower in the hull than the other occupants, this design decision once again being related to the downward angle taken by the propeller shaft running from the engine compartment at rear down into the gearbox at front. The gunner and loader sat on the turret basket floor in an elevated position when compared to the driver and bow gunner while the tank commander was seated still higher in the turret with quick access to his commander's hatch. A standing position could be attained by the tank commander via a flip-down circular seat for him to stand on. This allowed for the tank commander to rise up above his hatch and complete the ever-universal image we all have of a tank commander positioned chest-high out of his tank, assessing the battlefield before him.
The bow gunner doubled as the assistant driver though he had none of the driver controls allocated to his station. In the event that the primary driver would become incapacitated, the bow gunner could double in his place. The bow gunner's position required him to be seated at the right front of the hull where his station was primarily dominated by the tail end of his bow-mounted 7.62mm anti-infantry machine gun in a limited-traverse mounting. Like the driver, the bow-gunner was also given the use of a fixed periscope after the dropping of the direct vision slots mentioned earlier. The bow gunner's position proved useful in engaging and suppressing known enemy positions (as related to infantry) - an important component in the Sherman's arsenal when combating anti-tank gun crews. To prove the position more important, the bow gunner could also "mark" targets or help "range" the main gun onto a target (or suspected enemy location) via his machine gun tracer rounds which could be utilized to orient the gunner's cannon with. To the rear of the bow gunners seat was the floor-mounted emergency escape hatch fitted to allow the occupants of the Sherman an alternate, and somewhat safer, means of exiting the tank should the turret and twin top-mounted hull hatches be blocked or made impassable. Both forward positions (driver and co-driver) were given individual armored top-mounted hatches for direct entry and exit.
As exemplified in modern main battle tank systems, the bow gunner's position has been removed altogether, with self-defense handled by the gunner, loader or commander and their applicable machine guns while ranging is handled by complex laser ranging systems.
The gunner was afforded one of the most important jobs inside the Sherman in the firing of the main gun. By training order, the tank commander would verbally call out the target (signifying the target's type in the process), its location and what projectile to load. The loader processed the available information immediately and loaded the fresh ammunition round into the gun's breech. The gunners job was to traverse the turret in the desired location based on his commander's description and line up the target, adjusting for ammunition type and target distance. The gunner had the ability to rotate the turret at full speed and gradually decrease speed once he approached the targets general direction. Once lined up with the target, the gunner would affirm the commanders verbalized target parameters and take precise aim through his available scope. To complete the firing action, the gunner flipped the fire switch and depressed a foot pedal which activated the main guns firing solenoid, caused the main gun to ignite the propellant cartridge at the base of a given projectile munition and subsequently force the projectile out of the barrel and towards the target.
It can be surmised, the loaders job was to load the main gun. This was done by the loader pulling back on a lever located on the breechlock and then depositing a "fresh" projectile round - AP (Armor Piercing) or HEAT (High-Explosive Anti-Tank) - into the breech, depending on what type of targets were called out by the tank commander. Upon hearing the target call, the order was then given for which type of round the loader was to load. Most experienced loaders generally knew from past engagements what type of shell to load once the target type was called out. Generally, only the lead tank in any column was armed with a ready-round as this was done for safety purposes so the rear portion of the column would not accidentally open fire on the forward portion in the event of an ambush. This did well in keeping friendly tankers safe from one another, but in the heat of battle, it counted seconds against a tank crew's response time once the enemy had either opened fire or revealed themselves to the column.
The main gun loading action was set once the breechlock was closed and the firing pin automatically cocked. Upon receiving a physical signal - in the form of a nudge or kick - from the loader behind him, the gunner would then be free to fire the loaded projectile at will. The firing action recoil effect would then launch the spent shell casing out of the breech and onto the floor of the turret basket, leaving the breechlock open to receive the next round. This action was repeated by the loader and gunner as many times as needed under the direction of the tank commander. More often than not, gunners began to listen for the closing breech to signify the barrel was loaded and ready to go, not requiring a "go-ahead" from the loader - again, seconds were the difference between life and death on a World War 2 battlefield.
Despite US Army manuals dealing with verbal communications on how to handle the sighting, loading and firing actions in a Sherman, crews with enough experience together eventually learned to run things inside their tank through instincts and hand signals. Tank commanders still operated verbally for the sake of the entire crew but communications between loader and gunner could be made more efficient through the use of quick hand signals between the two. In a game of timing like that of a tank-versus-tank shootout, seconds count for everything in the survival of one's entire crew. It becomes easy to see how small-circle brotherhoods could evolve in such confined spaces where one man depends on the other to do his job to the fullest.
Notable Sherman Powerplants
Alongside their armament, the heart and soul of the Sherman lay in her selection of powerplants which themselves varied through production thanks to logistical shortages and performance limitations. The M4A3 fitted the Ford GAA. The Ford GAA was an 8-cylinder, liquid-cooled, gasoline-fueled engine with 450 horsepower at 2,600rpm that had its own origins as an aircraft engine. The engine itself was not well-liked by Sherman tank crews but serviceable nonetheless.
The M4A4 came online fitted with the Chrysler A57 "Multibank" gasoline-fueled engine. The Chrysler Multibank was named as such for it was essentially five commercial truck engines joined together in a "star" pattern. No doubt a system such as this proved to be a tank mechanic's worst nightmare. These engines proved the worst of the Sherman line and were therefore earmarked for export use and local state-side training of American tank crews.
Caterpillar offered a multi-fuel powerplant in diesel form from a revised Wright G200 air-cooled, gasoline system. The engine was retooled for diesel fuel use and became the Caterpillar D200A (later the Ordnance Engine RD-1820 series). These were limited production engines that were later dropped in favor of gasoline-fueled powerplants.
M4 Shermans earned a nasty reputation as exploding tanks after being directly hit, so much so that the tank earned the grim nicknames of "The Burning Grave", "Ronson" and "Tommycooker" ("The Burning Grave" was a term used by Polish tank crews while "Ronson' originated from a cigarette lighter of the time, one that would "light up the first time". Tommycooker was a British term for the Sherman based on a World War 1-era stove utilized in the trenches). Initially, this was associated with the engine catching fire (notably the gasoline-fueled types, forcing many-a-crew to distrust gasoline-fueled systems over the "more stable" diesel types) and ultimately exploding. Upon further review, it was found that the ammunition propellant charges were the true culprits of such interior explosions. The propellant charge had a natural tendency to violently react when hit by a flaming hot enemy projectile, resulting in an onboard ammunition explosion to the multiple available 75mm rounds. Some were so violent, in fact, that entire turret systems could be ripped clean off of their turret rings from such a result. As the worst fear of any tank crew was always (and continues to be) the idea of burning alive inside their tank, this proved to be a most unsettling characteristic of the Sherman production line, regardless of operating nationality. As a result, a revision in Sherman 75mm ammunition stowage practice did away with the twelve projectiles stored in the turret along with adding additional armor protection to those ammunition projectiles held in the side sponson storage racks. Later Shermans incorporated ammunition stowage under the turret basket floor and these could further be wrapped in containers for increased protection.
Ammunition storage varied in the M4 Sherman series as 75mm ammunition was organizationally strewn about the compartment. This included storage areas in the floor, turret and hull sponsons as well as a "ready" rack for quick access. 12.7mm ammunition was carried in the front right of the hull next to the assistant driver's position and along the turret floor. 7.62mm ammunition was stored at the assistant drivers position, in large supply behind the driver, along the tank floor and on the turret floor. Since crew-served weapons such as the M1 Thompson and (later) M3 Grease Guns were standard fare, .45 caliber machine gun ammunition was also stored in the turret. In addition to crew-served weapons, it was typical for a Sherman crew to carry a supply of twelve hand grenades for self-defense.