Saturday 20 July 2019

A Tank for Allies

The American Medium Tank M4 became the second most numerous tank produced in WWII after the T-34, and the first if you count the T-34-85 separately. This record did not come easy. It is often said that this result was reached by converting the American car industry to war footing, but there was only one automotive giant that built Sherman tanks: Ford. The M4 was assembled at specially built tank arsenals, as well as railway car companies and steel foundries.

There was a great variety among types of this tank as well. There were five main variants with four different engines. The M4A4 version was the second most numerous, but the Americans hardly used any of them.

A child of the engine famine

As early as the summer of 1941 it was clear to William Knudsen, the head of the Office of Production Management, that using only the Continental R975 in medium tanks will be untenable. The appetites of the American and British militaries only grew. Production of 1000 tanks per month were planned in April of 1941. This number doubled by July. At this scale the supply of radial engines would simply not be enough.

A search for alternatives began in the summer of 1941. Initially, new engines were needed for the Medium Tank M3, but the Medium Tank T6 entered trials in September of 1941. This tank entered service as the Medium Tank M4A1. The first M4s with Continental engines began coming off the assembly line in February of 1942.

Overall view of the Chrysler A57 Multibank.

Help came from the automotive sector. The first company to give a solution was General Motors, who developed a dual version of their GM 6-71 diesel engine. The engine, designed with the help of the British Military Mission, was put into production as the GM 6046. It was installed on the M4A2 family of tanks. Another engine, a gasoline one, was designed by Ford. The 18 L V8 Ford GAA was initially designed for aircraft. It was used on the Medium Tank M4A3. It was the Ford GAA and its variants that became the best American tank engine of its time. The third engine was designed by Chrysler.

The same engine with the cooling system installed.

This engine is worthy of a lengthier discussion. Unlike Ford, which had an aircraft division, and General Motors, which built trucks, Chrysler had no divisions that had engines suitable for medium tanks. The heaviest vehicle in production was the 3 ton Dodge truck, equipped with a 6 cylinder linear engine with no more than 100 hp of power output. The Chrysler brand itself was reserved for light cars with 6 cylinder Flathead family engines. One of these engines with a volume of 4.11 L was designed for a new series of Chrysler S-Royal and Windsor cars. Surprisingly, this was the engine that the new tank engine would be based on.

Five linear engines were combined to make one engine. Shockingly enough, it worked, and worked quite well.

A configuration like the dual GM 6-71 was an option, but Chrysler went their own way. The power of two of these engines would not have been enough. Their solution was to combine five engines into a single unit, giving birth to a 30 cylinder monster named Chrysler A57 Multibank. In practice, this was still five separate engines. There was no joint crankshaft, and each engine worked individually. Each engine delivered power to a central crankshaft via a gear linkage. This engine was a terrifying sight to behold.

Cutaway diagram of the M4A4. The engine does not quite fit into the engine compartment.

The Chrysler A57 Multibank ended up being very heavy. The entire mass of the system was 2.5 tons. The size was another drawback. Either five ordinary radiators or one massive one were needed to cool the five engines. The designers picked the second option. The radiator turned out to be so huge that it did not fit into the engine compartment of the Medium Tank M3. For this reason, the engine deck had a bulge in it, and there was another bulge in the floor. This feature migrated to the Medium Tank M4. Another drawback is that the drive shaft ended up being as high as on the Continental R975.

This monster had its upsides as well. The design worked quite reliably and had sufficient power for a medium tank: 370 hp in normal operation and 425 maximum. This engine could also be produced by Chrysler itself, which stopped production of light cars in January of 1942.

The M4A4 from above.

The first order of business was to test the engine on a converted Medium Tank M3. Trials began on November 15th, 1941. In December, a decision was made to standardize this tank as the Medium Tank M3A4. The experimental tank travelled for 6500 km. Trials showed that the experimental engine needed a little more work, but overall it performed well. The engine compartment in the M3A4 had to be lengthened, and the bogeys spaced out further. The pilot Medium Tank M3A4 arrived at the Aberdeen Proving Grounds in February of 1942.

The decision to build a Medium Tank M4 with this type of engine was made around this time. The Ordnance Standardization Committee did not even wait for the first tank of this type to be built before giving it the name Medium Tank M4A4.

Fifth one out

While the Detroit Tank Arsenal geared up for production of the Medium Tank M3A4, work on its replacement was gearing up. The first pilot M4A4s were ready in May of 1942, around the time the decline of the M3 family began. The Medium Tank M4A1 entered production in February of 1942, and the first diesel M4A2s came off the assembly line in April. In June of 1942, when production of the M3A4 began, Ford was already producing the M4A3. There was no point in producing a tank with inherently poorer characteristics. Production of the M3A4 was merely a training step towards the M4A4.

The third pilot M4A4. Aberdeen Proving Grounds, May 28th, 1942.

The hull of the M4A4 had to be lengthened from 509 cm to 606 cm. The mass of the tank increased to 31.6 tons. The M4A4 was not the heaviest: the M4A2 was 200 kg heavier. The M4A4 also had increased distance between the bogeys. The number of track links per side increased from 79 to 83. The ground pressure decreased a little. Trials showed that the mobility of the M4A4 was on par with the other members of the M4 family. The lengthened engine compartment and spaced out bogeys allow us to easily distinguish between this tank and other variants.

The tank can be identified by the lengthened engine compartment and spaced out bogeys.

Successful trials opened the way to production. The Detroit Tank Arsenal began executing on contract T-2593 in July of 1942, finishing two tanks with serial numbers 4805 and 4906 before the end of the month.

Initially, the goal was to produce 1400 tanks, with the last one built in January of 1943. However, there was a deficit of M3A4 tanks, with only 109 delivered. To make up for it, an extra M4A4 was produced in April of 1943, giving 1401 M4A4 tanks built in all.

Since production of the M4A4 began later than the M4A1 or M4A2, it received a number of improvements right off the bat. The M4A4 was never produced with a pair of hull machinguns, which were deemed ineffective. Later, in the fall of 1942, the direct vision ports for the driver and his assistant were removed. The M4A4 also started production with a turret equipped with the latest type of periscopic sight, introduced in April of 1942. Tanks built for contract T-2593 had serial numbers from 4805-6204 and registration numbers U.S.A. W-3056615-3058014. The 1401st tank was an exception, with serial number 56620 and registration number U.S.A. W-3098786.

Two more signature features of the M4A4: a bulge in the engine deck above the radiator, a sloped rear plate, and a two-piece door to the engine compartment.

The first tanks arrived at the Desert Training Center in August of 1942. The tanks turned out to be quite reliable, but service turned into a nightmare for its crews. Each engine had its own water pump with its own linkages. Even though there was a large maintenance door in the back, the linkage belt could only be replaced if the engine was extracted from the tank. As mentioned above, the engine weighed 2.5 tons. Because of this it was quickly decided to not send the M4A4 to the front, but use it as a training tank.

Assembly of M4A4 tanks at the Detroit Tank Arsenal, 1942.

This decision could have meant the end of production, but a customer was soon found: the British army. The British became active users of the M4A4. Why would they use a tank that the Americans rejected? Short answer: reliability. According to data given to the GBTU by the British, the M4A4 (Sherman V) was the most reliable tank from the M4 family. The mean distance between refurbishments was 3200 km for the M4A2 (Sherman III), but 4000 km for the Sherman V. This explains why the British were not fazed by difficulty of servicing the engine.

Servicing the Chrysler A57 Multibank was a nightmare for the crew. This photograph shows the mess of water pump linkages. It was impossible to service these without removing the engine from the tank.

Production of a second series of M4A4 tank began in November of 1942. Production for contracts T-2593 and the new T-3333 went on in parallel for some time. In December of 1942, the Detroit Tank Arsenal built a record number of tanks: 907. This was a world record in tank building. The second place goes to Soviet factory #183. In December of 1942 it delivered only 758 T-34 tanks. The Detroit Tank Arsenal went on to produce 600-650 tanks per month.

Contract T-3333 is linked to another record. It was the largest order for Sherman tanks: 4000 in all. Most of these tanks were built by the end of May of 1943, the rest were delivered in June. Initially, the tanks built for both contracts were identical. A change was introduced in May of 1943: the M34A1 gun mount. Unlike the M34, it was equipped with a telescopic sight. M4A4 tanks built for the second contract received serial numbers 16555-20554 and registration numbers W.3029082–3031158.

Tanks from the second series on maneuvers. The M4A4 was only used for training by the US army.

The third production contract, T-3606, was executed on starting in May of 1943. It ordered 3350 tanks. A new change was introduced starting with the first tank of this series. Tank #20555 had one water pump instead of five, which made the mechanics' job easier. Another novelty was the addition of applique armour to protect ammunition stored in sponsons. Armour was installed starting in August of 1943, and also appeared on some older tanks that went through modernization. Extra armour was also welded onto bulges in front of the driver and assistant driver positions.

A modernized A57 engine, used in M4A4 tanks starting with the third production series.

The M4A4's star started to wane by the fall of 1943. Instead of 3350 tanks ordered by contract T-3603 only 2098 were built. They received serial numbers in the ranges of 20555-22631 and 22632-22652, with registration numbers U.S.A. W-3029082–3031158 and 3031162–3031182. On September 10th the factory finished its 21st tank for the month and began preparing for production of the Medium Tank M4A6. However, only 75 of those were built. After that, Detroit retooled for production of the Medium Tank M4.

The M4A4 was the first of the M4 family to fully cease production. This early departure meant that these tanks never received wet ammo racks, cast transmission covers, 76 mm guns, or many other improvements. Nevertheless, this tank became the second most numerous of all "regular" M4s with 7499 units built.

A typical M4A4 in its final configuration. The tank has additional hull and turret armour.

As mentioned above, the US army only used the M4A4 for training. Only 56 were kept. The lion's share went to the British, 7176 tanks in all. 274 were sent to other countries, mostly France. Two tanks were sent to the USSR. Let's discuss those in detail.

Supersized portions

The Soviet military first learned of the Medium Tank M4A4 in the fall of 1942. A group of Soviet specialists visited the Detroit Tank Arsenal from September 3rd to September 5th, 1942. This group included Lieutenant Colonel Demyanenko and engineers Prishepenko and Sorvin. The latter composed a detailed report about their trip. This document contains a number of interesting notes about the reason behind the development of the Chrysler A57 Multibank. It became known that the GM 7-61 was in demand by other customers: the Canadians were using them in their Valentine tanks and the US Navy made a large order for the naval version (Gray Marine 6-71). This is why another type of engine for tanks was needed.

A shipping manifest for one of the two M4A4 tanks that arrived in the end of May of 1944.

Two Chrysler engines were shown to the Soviet specialists. One had been working nonstop for 300 hours by that point, the second for 400 hours. These engines showed a very long lifespan. The Americans also showed the production power of the Detroit Tank Arsenal, since a Soviet factory director was also present. The group was told that the factory was gearing up to produce 1000 tanks in December. This number was not reached, but the record was set anyway.

Sorvin evaluated the M4A4 as equal to the M4A2. Both of these tanks were superior to the M3. It was pointed out that the Chrysler A57 Multibank could run on low octane fuel and was water cooled, unlike the M3, which needed high octane gasoline and was air cooled.

Tank U.S.A. W-3057484 used in trials in the summer of 1943.

The GBTU was interested in the American design. The M4A2 was considered more interesting due to its diesel engine, but deliveries came irregularly. Only 36 tanks arrived in 1942, and 173 in the first half of 1943. This was caused by the fact that the M4A2 was used by the American and British armies. The volume of production was also limited by engine production. In these conditions the M4A4 could have become an acceptable replacement until the M4A2 was available in larger numbers.

The second tank, registration U.S.A. W-3057449. The gun mantlet has a counterweight, which was later removed. This tank can be seen on display at Patriot Park.

The first M4A4 tanks could have been shipped as early as the spring of 1943. However, the GBTU approached this issue very carefully. In early 1943, the GBTU rejected the proposal to send Crusader III tanks (they would have arrived in March of 1943). The M4A4 was the first tank where a small number was ordered for trials. 

These tanks were typical for summer-fall 1942 production.

A trial batch of two tanks came through Iran in late May 1943. These were tanks with registration numbers U.S.A. W-3057484 and 3057449 built in October of 1942. The engine was not the only distinguishing feature from the M4A2. The tanks were equipped with metallic T54E1 tracks with chevrons, instead of T41 rubber tracks. The M4A4 used a hydro-electric turret traverse mechanism, while the earlier M4A2s had a hydraulic traverse.

The bulge on top of the engine deck is seen from above.

Both tanks were sent to the NIBT proving grounds in Kubinka. On June 13th, two weeks after the tanks' arrival, tank U.S.A. W-3057484 was sent for trials. A widespread trials program was composed. The tank was to drive for 2000 km, 500 of which were on a highway, 1000 on dirt roads, and 500 off-road. The armament and crew comfort would also be evaluated. Since the tank had a new type of track with chevrons, it was necessary to evaluate their effectiveness.

The direct vision ports for the driver and his assistant were removed in the fall of 1942. The tanks that arrived in the USSR were among the last to have this feature.

The tank already drove for 202 km before the start of the trials. During the trials it travelled for another 1850 km, of those 1296 on a dirt road, 564 on a highway. Trials began on June 13th and ended on August 18th. The tank travelled its 1850 km in 15 days, then had to pause while waiting for spare parts to arrive. Trials used domestic B-70 gasoline with the addition of R-9 aircraft additives, as well as MK aircraft oil.

The armament was tested in limited volumes. The machinegun was not fired. The 75 mm gun fired only 82 rounds. Rate of fire was 12-16 RPM, lower than the 20 RPM recorded on the M4A2. This was because the M4A2 was tested in the spring, when there was less dust when shooting. The rate of fire on the move was the same: 5 RPM with a stabilizer, 3.8 without. Firing with the stabilizer resulted in an 80% hit rate, firing without only 50%. The traverse mechanism was also improved compared to the hydraulic one. One drawback of the gunnery was a poor sight scale.

The same tank from the rear.

Mobility trails showed a top speed of 40.3 kph. This was much lower than the M4A2, which demonstrated a speed of 50 kph. Average speed on a highway was 33 kph for the M4A4 and 39.7 kph for the M4A2.

Fuel expenditure was an important parameter. Here, the gasoline engine showed itself poorly. The dual diesel engines consumed 167 L per 100 km (much less than, say, the PzIII Ausf.H), while the M4A4 consumed 309 L of fuel per 100 km. This was even more than the Medium Tank M3. 

Gunner's station.

Surprises also awaited the testers on the dirt road. The average speed of the M4A4 in these conditions was 16.5 kph, compared to the M4A2's 20.1 kph. Fuel expenditure grew to 509 L per 100 km. Even the M3 did not consume as much, only 441 L per 100 km. The M4A2 was the least greedy of all: 246 L per 100 km. One can only imagine how much fuel the M4A4 would consume while driving through mud.

The military had no interest in a medium tank that consumed as much fuel as a heavy one. One full tank could last the M4A4 for 182 km on a highway or 115 km on a dirt road. The M4A2 could travel 310 and 210 km respectively. The 30 cylinder engine was also too complicated and difficult to service. The only advantage of this engine was that it worked flawlessly. The only problems during the trials were with the running gear and oil filter. The oil consumption was much less than the gasoline: only 2 L for 118 hours of work.

New tracks with chevrons resulted in higher mobility than on the M4A2.

The last stage of the trials was driving on slopes and hulls. The maximum grade that the tank could climb was 27 degrees, after which the tracks started to slip. The engine power was sufficient to climb at a higher grade. The tank could drive a at a tilt of 26 degrees. It was noted that metallic tracks with chevrons work much better than rubber tracks used on the M4A2. Later, the USSR received M4A2 tanks with T54, T47, and the very similar T49 with different types of chevrons.

Driving at a tilt during trials. The M4A4 turned out to be too greedy, consuming enough fuel for a heavy tank.

The M4A4 was rejected as a result of these trials. The tank ended up being too complicated and expensive to operate. The supply of M4A2 tanks began to pick up by the end of 1943, and 471 tanks of this type came to the USSR before the end of the year. One of the two Soviet M4A4s survives to this day: U.S.A. W-3057449 can be seen in Patriot Park.

1 comment:

  1. The Detroit Tank Arsenal was government owned Chrysler operated, not Ford. Good info on stabilizer increasing accuracy. The inability of the Sherman to climb 30 degree slope due to track slippage is consistent with other sources.