Rapid advances in armoured vehicles during WWII meant that even very good designs did not stay at the top for long. This was especially noticeable in American tank building. In 1939, the Light Tank M2 and Combat Car M1 were at the top of technical progress, but they were replaced with the Light Tank M3 by the time the USA entered the war in late 1941. In 1942, the Light Tank M3A1 entered production, but it did not last long as America's main light tank. At the end of 1942, the Light Tank M5 was there to replace it, the last of the descendants of the Light Tank M2.
From aircraft engines to automotive
By the middle of 1940, it was clear that the US would not be able to hide behind an ocean forever. The rapid defeat of France and loss of a large amount of materiel by England in Operation Dynamo was a shock. The situation with drawn out positional warfare of WWI did not repeat itself. It was clear that, sooner or later, the Americans would have to fight. This time, they were destined to become one of the main forces in the new world war.
The American industry was moved to a wartime mode. This influenced the tank building program directly. While tanks were only produced at the Rock Island Arsenal before, now they were built at large factories that were only involved with civilian products before. The first tank of this type was the Light Tank M3, which entered production at American Car and Foundry's plant in Berwick. Previously, it built train cars.
A rapid expansion of tank production caused several problems, one of which was a possibility of an «engine famine». There was an alternative in the form of the Guiberson T-1020-4 aircraft diesel. It was even installed on production vehicles, but it was never a fully viable replacement option. In addition, the compact and powerful aircraft engines had their drawbacks, as they were difficult to use.
It is not surprising that a search for an alternative began. Linear diesel engines from trucks were explored, but, in the case of light tanks, this work did not progress past the experimental phase. The engine compartment of light tanks proved too small for these engines. As insurance, the Ordnance Committee authorised the use of Cadillac engines with automatic gearboxes in the Light Tank M3, known as GM Hydramatic.
The appearance of the luxury car manufacturer in the tank industry was not surprising. First of all, car companies were taking part in tank building more and more often. The widely known GMC M18 tank destroyer, as well as its precursor, the T49/T67, was designed and produced by Oldsmobile, a GM subsidiary. Second, Cadillac was already producing an engine that would have been ideal as a tank engine. Known for its use in the Cadillac Series 42 cars, this 5.7 L V-shaped 8-cylinder engine was in production since 1936. Initially, it had an output of 135 hp, but this number was raised to 148 hp in 1941. Cadillac plants that were not already building army trucks began building tanks.
A Light Tank M3 with serial number 752 and registration number U.S.A. W-303740 was taken for experiments. The new engine forced a serious redesign of the engine compartment. A characteristic «hump» appeared, but it had almost no impact on the tank's characteristics. The hump was needed to house radiators. The mass of the tank, on the other hand, grew by 1134 kg.
Another feature of the vehicle, indexed Light Tank M3E2, was the combination of the engine and gearbox. The engine power travelled to a distribution box, then to the differential, which was the same design as the one used on the Light Tank M3.
Despite the drawbacks of the conversion, the fate of the tank with two engines was different from that of other engine conversions. Two two engines put out a combined power of 296 hp, which compensated the increased mass. The crankshaft from the gearbox to the differential was much lower, which made the turret crew's jobs noticeably easier. Automotive engines and gearboxes turned out to be a lot easier to service. Finally, the issue with overheating, bound to happen with air cooled aircraft engines, disappeared.
The advantages of the Light Tank M3E2 were so obvious, that, on November 14th, less than a week after trials at the Aberdeen Proving Grounds began, the Ordnance Committee decided to dub the tank Light Tank M4. However, it was not destined to enter production with the same hull design. In October, work on a Light Tank M3 with a new front hull began. This tank was indexed M3A1E1, and work on it reached the full scale model stage. On November 21st, the Committee decided to transfer the work to the Light Tank M4 chassis. The existing Light Tank M3A2 was converted.
The vehicle, indexed Light Tank M3E3, also received the D58133 turret with a stabilizer, hydraulic turret traverse mechanism, and turret basket. The same turret was later used on the Light Tank M3A1. The difference was that this time, the height of the basket was greater, and the traverse mechanism was hidden underneath, thanks to the lower crankshaft.
The reworked tank entered trials in early 1942. After improvements, only the lower part of the hull and suspension remained from the original tank. Thanks to the sloped front hull, the resistance to shells increased, which the armour thickness remained the same. The front of the hull was removable, to allow access to the transmission. There were some issues with vision, but they were solved by installing periscopes in the hatches of the driver and his assistant. In addition, the seat could be elevated on the march, greatly increasing visibility. The hull sides were also altered, and the hull was now assembled by welding.
The tank entered production in this configuration in February of 1942. However, a decision was made to no longer use the index Light Tank M4 in relation to the vehicle. Production of the Medium Tank M4 was starting up around that time, and the tank was renamed to Light Tank M5 to avoid confusion. Another addition was a fixed machine gun in the front of the hull. The Ordnance Committee added it in, since the tank had no sponson machine guns.
Main light tank of the second half of the war
As mentioned above, mass production was arranged at Cadillac factories. One cause for this was that American Car and Foundry was still building the Light Tank M3, which was to remain in production. The USA already entered the war, and their light tanks were fighting the Japanese, with mixed results. The army needed more and more tanks.
The first tank with registration number U.S.A. W-3046702 left the factory in Detroit in April of 1942. In June, the first tanks of this type were taking part in exercises. The new tanks were received well, since it was easier to use them than the Light Tank M3. However, this did not prevent the Light Tank M3A1 from remaining in production. It was necessary to saturate the army with new tanks, and parallel production of two models with different engines was acceptable.
There were, however, complaints about the tank. The hull machine gun, sticking out like a unicorn horn, was not particularly useful, and it was quickly discarded. There were also issues with removing the transmission, which were later solved by increasing the size of the removable section of the hull.
In the summer of 1942, General Motors, the owner of Cadillac, began to search for an additional production facility for their tank. This was the South Gate Assembly factory in California. The first tanks left the factory in August of 1942. Another producer of the tank was the Massey-Harris company from Georgia, which previously produced tractors. The first Light Tanks M5 left the factory in July of 1942. Meanwhile, the use of the tank revealed issues with ventilation of the driver's compartment. It was resolved on later vehicles by installing a fan between the driver and his assistant. 2074 tanks of this type were built overall, 1470 by Cadillac, 534 by South Gate Assembly, and 250 by Massey-Harris.
By the time combat started in North Africa, the 2nd Armoured Division already had Light Tanks M5, as well as individual tank battalions. The 1st Armoured Division also transferred its M3s and M3A1s to the French and moved on to M5 tanks, which illustrates the army's position opinion of this model. M3A1 tanks survived for longer in the Pacific, but were later replaced with M5s.
The question of further modernization of the Light Tank M5 was raised in the summer of 1942. It was directly linked to the deep modernization of the Light Tank M3A1, which resulted in the Light Tank M3A3. A noticeable improvement of this tank was an enlarged turret, with a large bustle. The radio migrated from the hull into the bustle. The enlarged turret had a positive impact on crew conditions, and additional observation devices in the roof improved visibility. Naturally, the military wanted to have the improved turret in the Light Tank M5. The M5 with an M3A3 turret was approved on September 24th, 1942, under the index Light Tank M5A1. After the installation of the turret, the vehicle's design was finalized.
Production of the Light Tank M5A1 began in November of 1942, with the Cadillac factory moving to the new model first. A month later, South Gate Assembly and Massey-Harris joined in. It was quickly understood that the addition of an observation port in the turret was a bad idea. The crews rarely used them, and large handles, which stuck out at temple height, did not add to the crew's comfort. Turrets with these ports did not remain in production for long.
The ports were initially welded over, and promptly removed altogether. Around this time, hooks for grousers (spurs) were added to the sides of the turret. These spurs were attached to the tracks in difficult road conditions.
Rapid production of new tanks allowed to dispose of Light Tanks M3A1 that were still serving in combat units. Additionally, production of a tank with a superior engine meant that the Light Tank M3A3 was no longer needed. The American army did not retain these tanks, and most of them ended up in other countries via the Lend Lease program. In August of 1943, the last M5A1 left the South Gate Assembly factory. In total, it produced 1196 tanks. A third producer was added again in October of 1943: the American Car and Foundry plant in Berwick.
The decision to replace the M3A3 wit the M5A1 turned out to be correct.
The Light Tank M5A1 transformed close to the end of 1943. A special «pocket» for hiding the AA machine gun was added on the side of the turret. In connection with this, the hooks for spurs were moved to the back and the left side of the turret. A large box for personal belonging was added to the back of the tank. The design of the sand shields also changed, making it easier to service the suspension. These sand shields were not installed on all vehicles. The tank remained in this form until the end of production.
By the spring of 1944, production of the Light Tank M5A1 slowly dwindled. It was clear that this kind of tank was obsolete. However, the tanks that were still in service did not go anywhere. The M5A1 slowly pushed out M5 tanks with less comfortable turrets, although tanks of this type remained in service until the end of the war.
The M5 was the only American light tank that was never sent to the British via the Lend Lease program. The cause of this was the rapid appearance of the Light Tanks M3A3 and M5A1, with better turrets.
Production of M5A1 tanks in Berwick ceased in April of 1944. They built 1000 tanks of this type. Cadillac ceased production in May of 1944. Overall, Detroit produced 3530 tanks of this type. The last tank was built in June of 1944 by Massey-Harris, which put out 1084 M5A1 tanks. Including the 1196 tanks built by South Gate Assembly, 6810 M5A1 tanks were built between December of 1942 and June of 1944.
The M5A1 was not only the most numerous light tank to use Harry Knox's suspension, but the longest serving front line light tank. Its debut was the landing in Italy, and it participated in all major American operations in Europe. Even at the stats of its fighting career, the armour and armament seemed obsolete. Nevertheless, the vehicle managed to do its job as a reconnaissance tank. In addition, the enemy of the Light Tank M5A1 was rarely another tank. There were plenty less protected targets for it to fight. In other words, the light tank could handle any task that was thrown at it.
The tanks were used en masse in Normandy and subsequent battles in Western Europe. Around this time, the main enemy of American tanks was infantry armed with Panzerfaust and Panzerschreck grenade launchers. For this reason, the tanks were equipped with improvised protection. Most often, it consisted of sandbags, attached to the front and sides of the hull.
Even though the superior Light Tank M24 entered service, the M5A1 remained the main light tank of the American army until the end of the war.
The supplies of the M5A1 to the Allies should be mentioned separately. 1431 tanks of this type were sent to Great Britain, where they were indexed Stuart VI. Unlike other tanks sent to the British, the changes made to the Stuart VI were minimal. The most noticeable change was the addition of smoke grenade launchers on the right side of the turret. These tanks were used en masse in Normandy. The appearance of new light tanks didn't mean that old tanks, including the Stuart III, were phased out.
Arrived too late
Unlike the USA and Great Britain, the USSR was cool towards light tanks. Even the modernization of the T-70, which led to the T-80, was more of a half-measure. As for American tanks that were sent through the Lend Lease program, the feelings about them were even more mixed. The cramped fighting compartment of the Light Tank M3A1 added fuel to the fire. Trials of the "M3 light mod. 1942" ended in late February of 1943, and supplies of these tanks ended in April. On one hand, this was because production of these tanks ended. On the other hand, the USSR didn't particularly insist on keeping them coming.
Despite this kind of attitude towards American tanks, the USSR did receive improved M5A1 tanks. As with the M3A1, the tanks were sent through the south route, through Baku. This time, the purchase was not large. According to the agreement, the USSR received five tanks to try out. The first two came in July of 1943, two more in August, and the last in September. A number of documents recorded them as «M3 light», which caused confusion. However, this was specifically the M5A1. The USSR received mid-production tanks: without an AA machine gun pocket, but already without observation ports in the turret.
The trials program of the Light Tank M5A1 in summer and fall conditions was composed in August of 1943. The vehicle would travel 1000 km in total, 250 on a highway, 500 on dirt roads, and 250 off-road. In reality, the tank was never driven off-road, only on paved and dirt roads.
The tank arrived without a full set of documentation, which led to some incorrect conclusions being made. Instead of the maximum engine power, the nominal power (110 hp x 2) was recorded. This led to incorrect conclusions regarding the power to weight ratio. 15.7 hp/ton was recorded, instead of the real 19.5 hp/ton. The mass was also incorrectly evaluated: 14 tons instead of 15.2
Despite its increased mass, the M5A1 was faster than the M3 and M3A1. The top speed achieved during trials was 60.3 kph, a little higher than the claimed top speed. The fuel expenditure was not much higher than that of the M3: 135 L for 100 km. The average speed of the tank on dry dirt roads was also higher than that of the M3: 23.4 kph. On this terrain, the fuel consumption was 197 L for 100 km. The M5A1 had a total fuel tank capacity of 340 L, which meant that the range increased, despite the higher fuel consumption.
To compare, the Soviet SU-76M consumed 215 L of fuel over a 100 km dirt road trip.
The biggest issue with the American light tank in the USSR was that it arrived too late. A number of its characteristics were better than those of the Soviet T-70 tank, and it got rid of the drawbacks of the M3 and M3A1. However, in the second half of the summer of 1943, the fate of light tanks in the Red Army was sealed. Weak armour and armament meant there was no reason to continue using these tanks on the Eastern Front. Instead, production of the SU-76M was launched, which used the same components, but was far more effective on the battlefield. Continued orders of American light tanks were pointless in this situation.
Despite such a disappointing verdict, the Light Tank M5A1 returned to trials in the summer of 1945. The trials were rather unusual: driving through a swamp. The tank drove alongside the Bombarder B-3 (Armoured Snowmobile Mk.I). Trials showed that the tank can drive along the swamp, as long as its tracks do not submerge deeper than 40 cm. Any deeper, and the tracks would slip, and the tank would get stuck. Today, the tank is on display at Patriot Park.