War in North Africa and Europe
The British Army was the first to use the Light Tank M3 as the "General Stuart" in combat. From mid-November 1941 to the end of the year, about 170 Stuarts (in a total force of over 700 tanks) took part in Operation Crusader during the North Africa Campaign, with poor results. Although the high losses suffered by Stuart-equipped units during the operation had more to do with better tactics and training of the Afrika Korps than the apparent superiority of German armored fighting vehicles used in the North African campaign, the operation revealed that the M3 had several technical faults. Mentioned in the British complaints were the 37 mm M5 gun and poor internal layout. The two-man turret crew was a significant weakness, and some British units tried to fight with three-man turret crews. The Stuart also had a limited range, which was a severe problem in the highly mobile desert warfare as units often outpaced their supplies and were stranded when they ran out of fuel. On the positive side, crews liked its relatively high speed and mechanical reliability. The high reliability distinguished the Stuart from cruiser tanks of the period, in particular the Crusader, which composed a large portion of the British tank force in Africa up until 1942.
In the summer of 1942, the British usually kept Stuarts out of tank-to-tank combat, using them primarily for reconnaissance. The turret was removed from some examples to save weight and improve speed and range. These became known as "Stuart Recce". Some others were converted to armored personnel carriers known as the "Stuart Kangaroo", and some were converted command vehicles and known as "Stuart Command". M3s, M3A3s, and M5s continued in British service until the end of the war, but British units had a smaller proportion of these light tanks than U.S. units.
The other major Lend-Lease recipient of the M3, the Soviet Union, was even less happy with the tank, considering it under-gunned, under-armored, likely to catch fire, and too sensitive to fuel quality. The M3's radial aircraft engine required high-octane fuel, which complicated Soviet logistics as most of their tanks used diesel or low-octane fuel. High fuel consumption led to a poor range characteristic, especially sensitive for reconnaissance vehicle. Also, compared to Soviet tanks, the M3's narrower tracks resulted in a higher ground pressure, getting them more easily stuck in the spring and autumn mud and winter snow conditions on the Eastern Front. In 1943, the Red Army tried out the M5 and decided that the upgraded design was not much better than the M3. Being less desperate than in 1941, the Soviets turned down an American offer to supply the M5. M3s continued in Red Army service at least until 1944. The Soviets did appreciate the high reliability of American tanks.
War in the Far East – CBI and Pacific
The U.S. Army initially deployed 108 Stuart light tanks to the Philippines in September 1941, equipping the U.S. Army's 194th and 192nd Tank Battalions. The first U.S. tank versus tank combat to occur in World War II, began on 22 December 1941, when a platoon of five M3s led by Lieutenant Ben R. Morin engaged the Imperial Japanese Army (IJA) 4th Tank Regiment's Type 95 Ha-Go light tanks north of Damortis. Lt. Morin maneuvered his M3 off the road, but took a direct hit while doing so, and his tank began to burn. The other four M3s were also hit, but managed to leave the field under their own power. Lt. Morin was wounded, and he and his crew were captured by the enemy. M3s of the 194th and 192nd Tank Battalions continued to skirmish with the 4th Tank Regiment's tanks as they continued their retreat down the Bataan Peninsula, with the last tank versus tank combat occurring on 7 April 1942.
Due to the naval nature of the Pacific campaign, steel for warship production took precedence over tanks for the IJA, creating by default an IJA light tank that performed admirably in the jungle terrain of the South Pacific. By the same measure, although the US was not hampered by industrial restrictions, the U.S. M3 light tank proved to be an effective armored vehicle for fighting in jungle environments. At least one was captured in the Philippines.
With the IJA's drive toward India within the South-East Asian theatre of World War II, the United Kingdom hastily withdrew their 2nd Royal Tank Regiment and 7th Hussars Stuart tank units (which also contained some M2A4 light tanks) from North Africa, and deployed them against the Japanese 14th Tank Regiment. By the time the Japanese had been stopped at Imphal, only one British Stuart remained operational. Upon U.S entry into the war in 1941, it began to supply China with AFVs including the M3 Stuarts, and later M4 Shermans and M18 Hellcats, which trickled in through Burma and formed part of the several well-equipped, well-trained armies that the Chinese Nationalists could deploy. These units were responsible for stopping numerous Japanese attacks during the later phases of the war.
Although the U.S. light tanks had proven effective in jungle warfare, by late 1943, U.S. Marine Corps tank battalions were transitioning from their M3/M5 light tanks to M4 medium tanks. With the less common supplement of their Type 97 Chi-Ha medium tanks, the IJA was left to do battle against U.S. Marine M4 Sherman medium tanks, with armor that had been designed and fielded in the 1930s.
When the U.S. Army joined the North African Campaign in late 1942, Stuart units still formed a large part of its armor strength. After the disastrous Battle of Kasserine Pass, the U.S. quickly followed the British in disbanding most of their light tank battalions and subordinating the Stuarts to medium tank battalions performing the traditional cavalry missions of scouting and screening. For the rest of the war, most U.S. tank battalions had three companies of M4 Shermans and one company of M3s or M5/M5A1s.
In Europe, Allied light tanks had to be given cavalry and infantry fire support roles since their main cannon armament could not compete with heavier enemy armored fighting vehicles. However, the Stuart was still effective in combat in the Pacific Theater, as Japanese tanks were both relatively rare and were lighter in armor than even Allied light tanks. Japanese infantrymen were not well equipped with anti-tank weapons, and as such had to use close assault tactics. In this environment, the Stuart was only moderately more vulnerable than medium tanks. In addition, the terrain and poor roads common to the theater were unsuitable for the much heavier M4 medium tanks, and so initially, for both sides, it was advantageous to deploy light armor. Heavier M4s were eventually brought to overcome heavily entrenched positions, though the Stuart continued to serve in a combat capacity until the end of the war.
Though the Stuart was to be completely replaced by the newer M24 Chaffee, the number of M3s/M5s produced was so great (over 25,000 including the 75mm HMC M8) that the tank remained in service until the end of the war, and well after. In addition to the U.S, UK and Soviet Union, who were the primary users, it was also used by France, China (M3A3s and, immediately post-war, M5A1s) and Josip Broz Tito's Partisans in Yugoslavia (M3A3s and few M3A1).
Post World War II use
After the war, some countries chose to equip their armies with cheap and reliable war surplus Stuarts. The Chinese Nationalist Army having suffered great attrition as a result of the ensuing civil war, rebuilt their armored forces by acquiring surplus vehicles left behind in the Philippines by the U.S. forces, including 21 M5A1s to equip two tank companies. They would have their finest hours during the Battle of Kuningtou in 1949, for which the tanks came to be known as the "Bear of Kinmen".
The M5 played a significant role in the First Kashmir War (1947) between India and Pakistan, including the battle of Zoji-la pass fought at an elevation of nearly 12,000 ft. The vehicle remained in service in several South American countries at least until 1996.
During the 1960s and 1970s, the Portuguese Army also used some in the war in Angola, where its all terrain capability (compared to wheeled vehicles) was greatly appreciated. In 1967, the Portuguese Army deployed three M5A1 Light Tanks – nicknamed "Milocas", "Licas", and "Gina" by their crews – in northern Angola, which served with the 1927th Cavalry Battalion commanded by Cavalry Major João Mendes Paulo, stationed at Nambuangongo. The vehicles were mostly employed for convoy escort and recovery duties, and limited counterinsurgency operations against National Liberation Front of Angola (FNLA) guerrillas, who dubbed them "Elefante Dundum”. "Milocas" was destroyed by an accidental fire in 1969, while "Gina" and "Licas" were withdrawn from active service in 1972, the former being sent to Luanda and the latter ended up in 1973 as an airfield security pillbox in the Portuguese Air Force’s Zala airfield. Period photographs show some modifications to the basic design, namely the omission of the bow machine gun, re-installed on a pintle mount in the roof of the turret, and a small searchlight fitted in front of the commander’s cupola.
The South African Armoured Corps continued to use M3A1s in a reserve role until 1955. Some were refurbished locally in 1962 and remained in service as late as 1964. The fleet was withdrawn in 1968, owing to parts shortage.
The M3 Stuart is still on the active list in the Armed Forces of Paraguay where the elderly survivors are the only tracked armor used by that country.