Saturday 18 March 2017

Light Tank M3A1: Basket into Battle

History knows many instances when an attempt to improve a design led to, if not a worse one, then at least an equivalent. The American M3A1 light tank is one such example. Even though its modernization improved some characteristics, the well-intentioned modifications had some unintended consequences. Let us go through them in order.

Stabilizer Consequences

The story of the Light Tank M3A1 begins with the gun. The armament of the Light Tanks M2A4 and M3 was the high scattering when shooting on the move. When firing in motion, only 4% of the shells struck their target. This result was nothing out of the ordinary for the time, especially for a light tank. In any case, the Light Tanks M3 and M2A4 did not have exceptional stability due to their small mass and high center of gravity.

The solution to the problem was the Westinghouse gyroscopic stabilizer, which was added to the M23 gun mount. Another novelty was the reworked M5E1 tank gun, standardized on November 14th, 1940, as the M6. The combination of the M23 mount and M6 gun showed much better results. Thanks to the stabilizer, the hit rate increased to 40%, a very respectable result. However, there were other issues. The previous gun mount, the M22, had a fine horizontal aiming system, and it was removed due to the addition of the stabilizer. This created major issues when aiming, since only the commander, also serving as the loader, could operate the horizontal turret traverse mechanism. This issue was resolved by adding a hydraulic turret traverse.

M23 gun mount with gyroscopic stabilizer, the main feature of the Light Tank M3A1

Trials at the Aberdeen Proving Ground showed the success of the idea of a hydraulic turret traverse. However, there was another problem. The crew did not sit in the turret, but stood in it. The ammunition racks, and, more importantly, tall driveshaft covered by a casing, were underfoot. While the turret was traversing, the gunner and commander had to leap over all of these obstacles. Now they had to leap faster, since the hydraulic turret traverse was faster than the manual one. This issue was solved radically: the tank received a turret basket and the gunner and commander were given seats.

The addition of a turret basket was a controversial solution, since it added problems as well as solved them. The driveshaft didn't go anywhere, so the turret basket could not be very tall. The gunner and commander were once again forced to tenaciously and courageously weather the hardships of military service, as the field manual dictates. More on that later. 

As you can see, the addition of a turret basket did little to improve the amount of space in the fighting compartment.

The change to the gun mount wasn't the only novelty. A whole new turret was designed for the modernized tank, the D58101, which had no commander's cupola, but received two hatches. The commander's cupola was not very useful, since the commander was on the other side, but the hatches that replaced it were in high demand, especially during evacuation. The commander received an observation periscope in the turret roof and the gunner received a periscopic sight. The AA gun mount moved to the rear of the turret, and its front plate was no longer removable. D58101 turrets were first used on regular M3 tanks, but they had no turret basket or hydraulic turret traverse mechanism.

The first experimental prototype of a Light Tank M3A1. The tank has a riveted hull.

The modernized Light Tank M3 was standardized under the index M3A1. The tank entered production in May of 1942. The hull was similar to its predecessor, but there were some changes. First of all, the military deleted the additional machineguns that were taking space up in the sponsons, as they proved ineffective. The portholes were sealed with caps. The freed up space was used to install a radio without reducing the amount of ammunition carried. Welding was now used during assembly of the hulls, but in limited amounts. The sides of the turret platforms were welded, and the hatch hinges were welded on. Later tanks only had a porthole with a cap on the right side.

The diesel version had longer air hoses from the engine compartment to the air filters.

The Light Tank M3A1 did not last on the assembly line. Production completed in January of 1943. 4410 tanks with a gasoline engine and 211 with a diesel engine were made. There was an attempt to set up production of welded tanks with homogeneous armoured hulls. These tanks would be called M3A2, but their production never began. As for the M3A1, its star set for obvious reasons. Production of the Light Tank M5 began at Cadillac in April of 1942, which had a better hull design, and the use of a pair of automotive engines was preferable. Another tank was designed to replace the M3A3, but more on that next time.

At the Periphery

Unlike the Light Tank M3, its successor saw its first battle with American crews. The 1st Armoured Division in Africa had 158 Light Tanks M3A1. Its first opponent in battle was French. On November 9th, 1942, a battle was fought between French Renault D1 tanks from the 2nd RCA (Régiment de Chasseurs d'Afrique, Regiment of African Hunters) and American light tanks, which were covering 75 mm M3 GMCs. As a result of the battle, the French lost 14 tanks and the Americans lost only one tank and one SPG. Soon, the light tanks from the 1st Armoured Division faced a more serious foe.

Tanks from the 1st Armoured Division in support of British infantry. Tunisia, 1943

On November 26th, 1942, the 1st Battalion of the 1st Armoured Division encountered Germant anks from the 190th Tank Battalion from the 90th Light Motorized Division. Light tanks supporting M3 GMCs attacked a column of PzIII Ausf. J and PzIV Ausf. G tanks driving from Mateur to Tebourba. This was the first battle between American and German tankers. An attempt to attack the enemy head on failed. The front plate of the PzIV Ausf. G was too thick, and shells from the M6 bounced off. Six Light Tanks M3A1 were knocked out in return.

American tankers changed up their tactics and hit the Germans from the flanks. This gave results: the Germans lost six PzIVs and one PzIII. One must give due credit to the tankers from the second company who managed to quickly evaluate the situation and execute a successful flanking attack. However, this is where their luck ran out. American light tanks could hardly measure up to German medium tanks in open combat. The 1st Division took particularly heavy losses in February of 1943, when it lost half of its tanks in a week. By that point, the role of America's main light tank had shifted to the Light Tank M5, and the road to Europe for its predecessor was closed. At least in American units.

Crew from the 3rd Battalion, 3rd Marine Division, Bougainville, 1943

On the other side of the world, the situation was different. Unlike the African or European theaters of war, tanks aged slowed in the Pacific. This was mostly caused by the fact that the Japanese tank industry lagged behind the rest of the world. The Ha-Go, developed in the mid-1930s, was still the main tank of the Japanese army. Even medium Chi-Ha tanks were not exactly advanced vehicles.

The conditions of the Pacific theater of war were such that often only light tanks could participate in battle. Such a situation developed in Burma. American early production light tanks lived here for a very long time, since they were up against a comparable enemy.

The Light Tank M3A1 made its debut on the Pacific Front in June of 1943. Light Tanks M3 have been completely removed from the American army by then, and the diesel version of the M3A1 was rejected by the army. The Marine Corps had a different opinion. They were much more interested in diesel tanks since they did not burn as easily and had a lower chance of stalling in the water during a landing. The marines tried to request tanks with Guiberson T-1020-4 engines. The marines' new tanks first landed on New Georgia in the Solomon archipelago. From then until the middle of 1944, the M3A1 was successfully used by the army and marines. The tanks also fought during the assault on the Betio atoll, which had exceptionally high casualties among the marines.

A flamethrower installed instead of the hull machinegun. This replacement proved unpopular

The American tanks could successfully fight Japanese tanks, but more often than not their enemy was infantry. Light tanks were not the best measure against it, since the fragmentation effect of a 37 mm HE shell was comparable with a hand grenade. A reasonable idea of equipping the tank with a flamethrower arose. The first tank was prepared in October of 1943. The hull machinegun was replaced with a flamethrower, and its fuel tank was mounted in the right sponson. However, this design was deemed poor.

American marines in front of a flamethrower Satan tank, 1944.

The debatable degree of success of the flamethrower M3A1 variant led to the development of another tank in February of 1944, known as Satan. These tanks were built in field workshops, as the conversion did not require significant effort. The tank's gun was removed, its mantlet altered, and a British Ronson flamethrower was installed. The first flamethrower tank was tested on April 15th, 1944, and the Marine Corps ordered 24 Satans as a result of the trials. 12 tanks were sent to the 2nd Division and the other 12 to the 4th. They were used in battle very effectively and for a long time.

Worse than before

The first Light Tanks M3A1 arrived in the USSR in late 1942, 340 tanks of this type were sent in total. It's impossible to determine how many arrived, since they were recorded as "M3l", and it's impossible to tell them apart from the Light Tank M3. 165 tanks arrived in January of 1943, 125 of them along the south route. A month later, only 37 tanks came, and deliveries continued to dwindle rapidly. The last tanks of this kind arrived in April, and 255 M3A1 tanks arrived in 1943 in total. The production of these tanks in the US had finished. However, there were other reasons why American tanks stopped coming over as a part of Lend Lease.

Tank with serial number U.S.A. W-3011743 during testing at Kubinka. The tank can currently be seen on display at Patriot Park.

The GABTU noticed the new variant of the M3. The tank with serial number U.S.A. W-3011743 arrived at the NIIBT Proving Grounds (recently relocated back to Kubinka). This vehicle was referred to as "M-3 Light model 1942".

Interestingly enough, our specialists determined that the gunner must be the commander, while in American units, the commander was doing the loader's job. Presumably, the commander also served as the gunner in Soviet M3l tanks. Aside from the new turret and partially welded hull, NIIBT workers pointed out the additional oil filter and a thermostat. An additional charging device placed underneath the turret basket was also noticed.

Same tank from the left.

The arrival of a modernized tank was an excellent excuse for winter trials. The tank drove for 929 km between December 18th, 1942, and February 21st, 1943. The first stage was 369 km long, 172 along the highway, 75 on dirt roads, and 122 off-road. The top speed of the tank on a highway covered with snow was 59.2 kph. The average highway speed was 45.2 kph, 27 kph on a dirt road, and 22.3 kph off-road. The fuel expenditure was 130, 217, and 252 L per 100 km respectively. The tank could drive in third gear along the snow covered terrain, but there was not enough engine power to shift any higher. The rubber tracks played a cruel joke: the tank drove into a ditch but could not drive back out since there was not enough traction. Repeated attempts to get out resulted in the left track slipping off.

Despite several welded connections, the tank continued to widely use rivets.

Trials continued with spurs installed on every track link. The tank drove for 391 km, 234 on a highway, 97 along a dirt road, and 60 off-road. The top speed dropped to 39.6 kph, medium speed to 33.4, 23.4, and 19.8 kph respectively. The fuel expenditure increased: 184 L per 100 km on a highway, 260 on a dirt road, and 316 off-road. The spurs improved traction, but at the cost of worse fuel economy and also more shaking. 169 km was also driven on a highway with 5 spurs per track. The reduction in the number of spurs reduced shaking, while the performance remained at an acceptable level.

The tank became stuck when trying to cross a ditch.

Of course, the main novelties in the "M-3 Light model 1942" were the new turret and fighting compartment. The testers were puzzled. The author had the chance to enter the turret of a Light Tank M3A1, and his experience was not a pleasant one. Presumably, the turret was designed for dwarves with very long and flexible necks. Otherwise, it is impossible to use the telescopic sight. Of course, it's not appropriate to complain about the height of the fighting compartment with a height of 192 cm, but as it later turned out, the author's conclusions coincided with the verdict made at the NIIBT proving grounds.

The position of the telescopic sight was considered very poor by Soviet specialists. It was located too low and too far. The gunner had no 360 degree vision. The turret traverse mechanism was very harshly criticized as well. On one hand, the time required for a 360 degree traverse decreased from 52 to 16 seconds. However, precision is also an important feature. The hydraulic drive had problems with that. As for the hand traverse, the inconvenient location of the turning mechanism, significant looseness, and an uncomfortable pose quickly tired the gunner.

The loader didn't fare much better. It was difficult to access the ammunition, and, according to the report, the loader needed help from other crew members to perform his job. The separation of radio components along both sides of the tank also caused little enthusiasm.

The only thing that caused legitimate interest was the stabilizer. Trials showed that it allowed for precise fire on the move with a rate of fire of 5-7 RPM. It's worth mentioning that the stabilizer from this American tank became the starting point for work on Soviet stabilizers.

The overall conclusions regarding the results of the trials were as follows:

  1. The tactical and usability characteristics of this tank are equal to those of the M3 light model 1941.
  2. The cramped workspace, poorly placed mechanisms, and wobbly gun lower the combat qualities of the tank.
  3. The hydraulic mechanism does not provide accurate aiming of the gun due to its poor sensitivity.
  4. Using the hydraulic stabilizer in motion increases the rate of fire to 5-6 RPM and increases the precision of fire.
  5. The small size of the periscopic sight markings make aiming and fire correction difficult.
  6. The telescopic sight is placed very low. It is not possible to use it to fire the gun.
  7. Access to ammunition in the fighting compartment is inconvenient. Ammunition in the hull can only be accessed with help from other crew members."
The crew's working conditions became poorer. The small turret hatches were also criticized. This is not mentioned in the report, but the handles of the turret vision ports were also poorly designed. They were long, stuck out around the head, and could easily injure the commander or loader. Overall, the combat qualities of the tank were considered worse than its predecessor's.

The installation of spurs improved the tank's ability to navigate snowy slopes, but the fuel expenditure increased and speed decreased.

Despite such harsh criticism, the new tanks lasted for a long time. The Light Tank M3A1 saw its first combat in the North Caucasus in late 1942 and continued to serve until 1945. These light tanks also fought in the infamous landing at South Ozereika on February 4th, 1943, where the 563rd Independent Tank Battalion lost its tanks. They fought in tank brigades and tank regiments attached to cavalry divisions. In some units, they lasted until the very end of the war.


  1. I think you mean "driveshaft", not "crankshaft". A crankshaft is the part inside the engine that the pistons spin around; a driveshaft or propshaft connects the crankshaft to the transmission. I also don't understand what this is about the "commander's cupola being on the gunner's side". I thought the gunner was on the right, the loader/commander was on the left.

    1. Thanks for the correction. As for the cupola, Soviet tradition was that the gunner was the commander in tanks with only two turret crewmen. Presumably Pasholok based his critique on that convention.