Wednesday 16 November 2022

The Most American Sherman

A number of different fates could befall a Sherman tank. They fought in the deserts of Africa, the jungles of South-East Asia, the steppes of the Soviet Union. Tanks build at American factories could end up anywhere and fight with any crew, with one exception. The Medium Tank M4A3 with a Ford GAA engine was almost guaranteed to be crewed by Americans. Let us tell the story of the Sherman tank that the American preferred to keep to themselves.

Ford vs. Wright

The American automotive industry made a large contribution to victory in WWII. As one of the largest automotive manufacturers, Ford couldn’t avoid taking part. The company began working on an analogue to the British Rolls-Royce Merlin in 1940. The Air Force rejected this V-12 engine, but soon it found a home on land. Like the Merlin, a version of which was used on Cromwell tanks, the new Ford engine could be used on American medium tanks.

Ford GAA engine, Saumur tank museum.

Work on a tank version of this engine began in September of 1941, before production of the Sherman began. Ford removed a third of the cylinders from the motor. It still put out 450 hp at 2600 RPM in this configuration, which was enough for its purpose. The engine weighed 709 kg, more than the radial Wright R-975, but Ford’s engine was 40-50 hp more powerful depending on the RPM. The new engine was put into production at the Lincoln factory in Detroit. It was named Ford GAA, but sometimes referred to as the Ford GAA-V8 or simply Ford V8. 

The Sherman tank equipped with this engine was indexed Medium Tank M4A3. As the hull shape was slightly reworked it ended up being even lighter than the ordinary M4 tank: 69,637 lbs (31,586 kg) vs 69,861 lbs (31,688 kg) fully stowed. The tank’s mobility was no worse than that of other Shermans. It could keep up with the diesel powered M4A2 even on difficult terrain. Both tanks finished a hilly 1.5-mile course at Fort Knox at the same time: in 4 minutes 22 seconds.

A cutaway drawing of the Sherman M4A3. The Ford GAA engine perfectly fit into the engine compartment.

Ford itself made relatively few tanks of this type: 1690 M4A3 Shermans left the factory in Highland Park between May 1942 and December 1943. Fisher Tank Grand Blanc built 3701 M4A3 tanks with 75 mm guns and 525 with 76 mm guns. Chrysler’s factory in Detroit built 4017 tanks of this type with a 76 mm gun and 3039 with a 105 mm howitzer. In total there were 12,596 Medium Tanks M4A3 built and 428 refurbished.

Like other Shermans, 10 M4A3s took part in reliability trials that took place in 1943. Ford’s motors performed splendidly. On average, the engines worked for 255 hours, although the first broke down after only 87 hours of working. Three more tanks were removed from trials at 187, 247, and 295 hours for reasons other than engine failure. The report noted that the broken engines could be put back into service by replacing just one part. The Ford engine was the easiest to service of all those tested. M4A3 tanks drove further than any other tank tested. Combined, the 10 Shermans covered 10,108 miles on a road and 10,328 miles off-road for a total of 20,336 miles or 32,743 km with a total of 2338 hours and 16 minutes of runtime. Even though conditions of the trials permitted replacing any component that was not inside the engine, a lifespan of over 3200 km per vehicle is quite impressive.

Early M4A3, view from above. The access hatches for engine maintenance can be seen on the engine deck. Early tanks did not have a loader’s hatch.

The average speed was lower than that of the M4A2: 9.25 mph (14.9 kph) compared to 9.5 mph (15.3 kph). However, this was still faster than the gasoline powered tanks. The M4A1 and M4A4 reached an average speed of just 8 mph (12.8 kph) in this trial. The M4A3 managed to maintain a higher speed and burn less fuel than these tanks. Its fuel economy was 0.87 mpg (270 L per 100 km) on a road and 0.40 mpg (588 L per 100 km) off-road. The average fuel expenditure was 428 L per 100 km, compared to 0.47 and 0.40 mpg (500 and 588 L per 100 km respectively) for the M4A1 and M4A4.

The M4A3 continued to lead in reliability trials. In trials held in the winter-spring of 1944 a tank with a new turret ring liner travelled for 2097 miles (3375 km) over the course of 203 hours and 25 minutes. Other tanks in these trials could not keep up: the M4 broke down after just 15 hours and 10 minutes of driving, after which it had to be replaced with another tank of the same type, the M4A1 held on for 27 hours and 15 minutes, and only the M4A4 got close, travelling for 1343 miles (2161 km) over the course of 149 hours and 35 minutes.

A late M4A3 with larger hatches for the driver and assistant driver, as well as a new turret.

Other reliability trials began around this time, although not very large scale ones. 20 Shermans of various types took part, including 4 M4A3s. This time the time spent on repairs was carefully recorded. Ford lost his title in this round. Engine service took 110 hours, which was better than the M4A1 (132 hours) or M4A2 (143 hours), but not as good as the M4A4, whose crews spent only 45 hours on engine maintenance. However, the M4A3 was still in the lead if you count other maintenance, for instance it took 112 hours to service the transmission on the M4A3 and 340 on the M4A4. The reliability of the suspension was about even. Not a single Ford engine lasted the whole trial, they were eliminated at 293, 302, 347, and 350 hours. Only three Chrysler engines and one GM made it until the end.

Friendly Trials

Even though the M4A3 was not in service with other nations, they were still shipped overseas for demonstration purposes. One tank of this type arrived at the Fighting Vehicles Proving Establishment (FVPE) in the UK. This tank was referred to as “General Sherman M4A3 (Ford Engine)”. The tank received the British WD number T.146190 in addition to its American serial number 2659.

There was little to distinguish the M4A3 from other welded hull Shermans from the front.

The British noted that the M4A3 was not radically different from tanks they’ve seen before. The differential cover was cast. The Oilgear powered traverse was used. The air filters were in the same place as on the M4A4 tank, but the layout of the engine compartment was closer to what was used on the M3, Ram, and Sherman II.

There were new features as well. The engine deck changed, now there was a shield underneath the air intakes designed to protect against Molotov cocktails. The testers knew nearly nothing about the engine at this time, only that it used a wet sump, a Cuno oil filter, and a new cooling system with two fans. Measurement of its characteristics showed that they were lower than advertised. The engine put out only 390 hp instead of 450, and the compression ratio dropped from 7.5 to 6.7.

The difference from the back is more noticeable: note the rear plate and grille protecting the air intakes.

The first week was spent thoroughly studying the M4A3 and performing brief trials. The tank arrived with new T49 metallic tracks. They were compared to T47E1 tracks where the inner side had a rubber pad. The British had only read about these tracks, but considered them preferable, as the steel surface of the T49 had a negative effect on the lifespan of road wheel tires.

The first tire was torn off after 102 miles (164 km) of driving, the second after 144 miles (231 km), and the wheel that replaced it lost its tire at 222 miles (357 km). At 335 miles (539 km) the British gave up and installed tracks with rubber pads. Notes mentioned that other Shermans had travelled up to 1000 miles (1600 km) at the proving grounds without showing such issues.

M4A3 tanks with T49 tracks were used on the front lines.

The fully metallic tracks did not perform well. The tank slid around on icy roads and in two cases even slipped into a ditch. The control rods must have been improperly tuned, as the testers noted that the tank steered sluggishly and turned with a delay. There was also a leak in the oil system. Testers noted that it was hard to get to it. Another new feature, a circuit breaker board instead of fuses, was also met with little enthusiasm. The circuit breakers had to be bypassed as they only worked when the button was held down. Without them trials could not continue.

The tank was considered in running order on January 16th and real trials began. The top speed attained in a quarter-mile race was 23.1 mph (37 kph) from a running start or 18.6 mph (30 kph) from standstill. The average speed was 20.6 mph (33 kph) on roads and 11.9 mph (19 kph) off-road in mud. The tank showed an average speed of 10 mph (16 kph) at the Beacon Hill track (460 m at a 5 degree slope).

Three types of Sherman track links: T49 (metallic with parallel grousers), T47E1 (metallic with parallel grousers and rubber padding on the inside), and T41 (rubber coated from both sides) as well as a removable grouser. Graphics from The Sherman Tank Site.

The engine broke down during these trials. A warning soon arrived from the US: the Americans warned that the tank’s performance may be atypical, as the engine was an old one without the latest improvements.

The broken tank disappeared from the proving grounds’ reports for two weeks. The engine was removed and examined by February 6th. The degree of cylinder wear was not high, except for the #4 cylinders on both sides. A new engine arrived in late February. The technicians who had to install it complained that the installation process was difficult. The water pump and oil lines had to be removed first, then the engine had to be lowered into the fighting compartment at a very precise angle to move it under the bracket that held the fans, as it could not be removed. The fans themselves and the radiator also had to be removed before the engine could be installed.

Air filters in the engine compartment.

The new engine was indeed an improvement. It worked at up to 2800 RPM compared to its predecessor’s 2400, which gave the tank extra speed: up to 28.45 mph (45 kph) with a running start or 22.1 mph (35.5 kph) on the quarter-mile track. The difference was not significant off-road, but the tank flew up Beacon Hill: the average speed was now 18.3 mph (29 kph). After a 1534 mile (2468 km) the speed dropped to 15.3 mph (24.6 kph), but this was still better than the first attempt. This new speed came at a cost: the water and air temperature were higher and the fuel expenditure increased: from 1.29 miles per British gallon to 1.09 (from 219 to 259 L per 100 km).

The trials didn’t finish without issues. An oil leak was found after 14 miles (22.5 km), the engine started losing power after 301 miles (484 km), and after 475 miles (764) the right cylinder bank began to misfire. The right magneto had to be replaced after 526 miles (864 km). Oil leaks continued, and at 713 miles (1147 km) water leaks were detected as well. Nevertheless, the tank made it to the 2000 mile (3218 km) mark.

By the end of the month the M4A3 had travelled for 2575 miles (4144 km) with a new engine, of that 1086 miles (1748 km) on a highway and 1489 miles (2396 km) off-road. In total the tank covered 3078 miles (4953 km). The Sherman was in rough shape, especially the transmission. A serious defect was found: a driveshaft failure. It was fixed, but the tank didn’t run for long after that. Over the last 1000 miles it also had issues with the grease glands and oil filter.

A Ford GAA engine on a repair stand. Graphics from The Sherman Tank Site.

Trials ended after 3189 miles (5132 km) and 259 hours of driving. The engine power didn’t drop radically until the end, but testers began to notice metal shavings in the oil filter and the oil consumption spiked. A detailed report on the trials was composed. The British suggested only two improvements: make the fan bracket removable and simplify the oil filling procedure.

American tank, British style

Even though the British found the tank to be very good, it was far from perfect. Even though it was not going to be adopted into service, it was still given the British style name “Sherman IV”. A modernization program was composed. The first step was to install a hatch for the loader. Combat experience showed that without his own hatch he was doomed if the tank caught fire. This hatch also came in handy during servicing of the tank. The second large change also impacted the loader. The recoil guard would be made collapsible. A new dust cover would have to be made for the breech, as the stock one was too small.

M4A3 in Brittany, August 1944. The Americans gladly used the tank that the British found many faults in.

The sights were also reworked. A vane sight would be installed for the commander and a locking screw would be introduced for the periscopic sight to lock adjustment. The M55 telescopic sight was deemed unserviceable. If the gunner’s eye was not in the center of the eyepiece then the visibility became very poor. Alas, there was no replacement. The tank also needed a turret traverse indicator. The markings on the elevation flywheel were converted to standard British ones.

The ammunition racks would also need improvements. According to the British, the build quality was poor, as the rounds got stuck in their slots. Some areas designated for machine gun ammunition storage were entirely unsuitable for the purpose, as the ammunition boxes didn’t fit. The machine gun tripod would have to be moved, as the assistant driver’s seat could not fold down with it in place.

Welding seams would also have to be redone. The British complained that the welding was poor in quality and entirely absent in some places. A buckle on one ammunition rack strap was not attached in place at all, another one was held in place only by paint. The report noted that these defects don’t radically degrade the tank’s performance, but they were indicative of negligent attitude on the part of the fitters.

A Sherman crew drinks tea. Tankers had a tendency to try and heat water directly in the tank, which was not a safe thing to do.

The ammunition rack with Thompson magazines was considered useless. It was hard to imagine that someone would stay inside a burning tank to individually take 20 magazines from their slots. The rack was replaced with an improved one where all magazines could be retrieved at once. A waterproof crate with ammunition, grenades, and rations was attached to the outside so the crew could still retrieve it if they could not stay in the tank. The British also recommended installing an electric stove in the tank. Crews at rest would always make tea, even if a fire could alert the enemy to their presence. Tankers would even periodically attempt to light a fire inside their tank if they were not allowed to exit, which was undoubtedly dangerous. An electric stove would solve these problems.

A modernized tank with the WD number T.150733 was presented for trials in the spring of 1944. The tank travelled for 3022 miles (4863 km): 1506 miles (2423 km) on a highway, 1516 miles (2440 km) cross-country. Major defects that required a stop did not occur in the first 1000 miles. Three serious defects took place before the 2000 mile mark: one with the carburettor and two with tracks. No more serious defects took place until the end of the trials, but 51 minor defects were recorded: 4 in the engine, 35 in the running gear and suspension (14 broken springs, two broken idlers, 19 destroyed road wheel tires), 7 defects to do with track links, and five in the electrical system. Oil leaks continued to plague the M4A3, as well as issues characteristic of other Shermans. Nevertheless, the reliability of the tank was still deemed excellent.

A tank from the American 9th Tank Division in Germany, April 1945. It was clear by then that the M4A3 became the American tankers’ favourite.

The M4A3 enjoyed a long career after the war. This tank remained the army’s favourite. Shermans of all other types were given away across the whole world while the M4A3 continued to serve at home. The M4A3 was used to develop the M4A3E2 “Jumbo” assault tank, M4A3R3 Zippo flamethrower tank, and the M4A3(105) howitzer tank. Variants of Ford’s GAA engine also came in handy to power the next generation of tanks, the T23 and T26, which then turned into the heavy M26 Pershing. The tank and its engine had their issues, but one can safely say that the M4A3 was the best of all Shermans.

  • Canadian Military Headquarters, London (1939–1947), RG 24 C 2
  • Pat Ware. M4 Sherman Tank Owners' Workshop Manual: 1941 Onwards (All Variants) — Zenith Press, 2012
  • Richard P. Hunnicutt. Sherman: A History of the American Medium Tank — Echo Point Books & Media, 2015

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