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M3 Grant I M3A1 M3A2

M3A5 M3A3 M3A4

Medium Tank M3 Lee^1-18,30-32

The medium tank M3 was based on the medium tank M2, utilizing its suspension, power train, and other mechanical parts. The M3 was called Lee I by the British, and the turret machine gun cupola was often replaced in British service with a flat rotating split hatch.

Late-production tanks had the doors originally on each hull side replaced by a floor escape hatch, but the right-side pistol port remained. Starting in March 1942, one of the driver's fixed machine guns was removed as well; the resulting hole was filled with a steel plug. The other bow machine gun omitted by June 1942. The crew of late M3s was reduced to six men when the driver also took over the role of radio operator. Very late production M3s had new heavy-duty suspension bogies with 8" (20cm) instead of 7" (18cm) volute springs, and the track return rollers were moved to the rear of the new bogies. Late vehicles also had a direct-sight telescope M15 installed to the left of the 75mm gun since it was difficult to maintain alignment with the original periscope M1, and another periscope was installed above the driver's position. High carbon monoxide levels in the fighting compartment led to the installation of two ventilators on the hull roof and a third on the turret roof. The engine intake and exhaust setup was shown to excessively heat the combustion air as well as produce undue exhaust backpressure. The engine air cleaners were therefore moved to the outside of the engine compartment, and the pepperpot exhausts were changed to fishtail exhausts with mufflers and modified exhaust collector rings with exits at the top of the engine. Before full production of the final redesign could be implemented, a quick-fix setup was used that included exterior air cleaners and straight exhausts with no mufflers.

The armament of late-model tanks included the M3 75mm gun and M6 37mm gun. The differences in the 37mm and 75mm guns are as follows: The 37mm gun M5 was 6" (15cm) shorter than the M6, and the M5 had a manually-operated breechblock instead of the M6's semiautomatic breechblock. The 75mm gun M3 had a longer barrel than the M2.

Gun stabilizers were installed in tanks manufactured by the Detroit Tank Arsenal by November 1941, and expanded to the rest of the production lines starting in January 1942. Tanks with stabilization systems installed can be differentiated from those without by the presence of a cylindrical counterweight under the 37mm gun, and a counterweight at the end of the 75mm gun barrel if the tank is armed with the shorter 75mm gun M2. The longer 75mm gun M3 did not require a counterweight to be compatible with the gyrostabilizer.

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Cruiser Tank Grant I^1-15,30

The British were not wholly satisfied with the design of the medium tank M3 and were permitted to make changes to the turret and fighting compartment. A new turret designed by Leslie Edward "Ted" Carr was used, and this featured a bulge at the rear for housing the radio, which was operated by the tank commander instead of a dedicated crewman. The turret machine gun cupola was also deleted, as its height was considered excessive on both the battlefield and the railroad: shipping tanks by train in England would require its removal. A 2" Mortar Mark I (smoke) was installed in the turret's front right corner. This was fixed in elevation, and 14 smoke rounds were carried. Initially, production of the mortars lagged, and a 1" (2.5cm) armor plug was therefore installed in its aperture in the turret casting. Ammunition stowage was modified after battle experience in North Africa to eighty 75mm and eighty 37mm rounds in British-designed armored stowage boxes.

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Medium Tank M3A1 Lee^{1-12,19-22,30}

Except for the cast upper hull, the M3A1 was largely identical to the M3. The door in the right side hull roof was placed on the rear slope of the 75mm gun sponson. This hatch was hinged from the front on early vehicles, and opened to the rear on later models. Cast hulls eliminated the need for bolts and rivets, which increased crew safety as well as decreased hull manufacturing and machining time (though a cast hull required about two weeks for the hardening and cooling processes, assembly of the cast hull required 100 man-hours compared to 1,100 man-hours for a riveted hull). Other benefits included the increased chance of ricochets due to its rounded shape, and also cheaper production which saved ~$3,000 per hull produced. The British referred to M3A1 as Lee II. The Guiberson T-1400-2 9-cylinder, 4 cycle, diesel radial engine was going to be used in M3A1s built by the American Locomotive Company, and these were designated as M3A1(diesel). This engine's low-end torque offered improved performance, and it increased fuel mileage over the gasoline radial. It proved unreliable in tests, however, and production plans were scuttled after 28 M3A1(diesel)s were manufactured.

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Medium Tank M3A2 Lee^{1-8,10-12,23,30,33}

The M3A2 was identical to the M3 except for the M3A2's welded hull. Welding the hull saved weight for a given ballistic protection level; removed rivet heads and angles on the tank interior, which increased crew safety; and shortened the time and cost of assembly. The British designation for M3A2 was Lee III.

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Medium Tank M3A5 Lee^{1-11,23-26,30}

The radial gasoline engines of previous medium tanks M3 were also needed for training aircraft, and an engine shortage was foreseen. To help with the situation, the General Motors 6046 diesel engine was created. This was a pair of GM 6-71 truck engines, each of which could be operated independently if so required. The engines were meshed together via a power transfer unit using a helical gear mounted on a propeller shaft connecting to the tank's transmission. The side and rear armor plates on diesel-engined M3s extended below the level of the track return run, and the rear hull plate was sloped to accommodate the larger diesel engine. Instead of the twin engine access doors found on radial-engined M3s, the lower rear hull was a single plate. An exhaust deflector was installed to reduce the dust signature of the tank, and two armored doors with air intake louvres were installed over the tank's engine compartment. During production, the gear ratio in the power transfer unit was changed from 1:1.19 to 1:1.37, increasing the top speed from 25mph (40kph) to 29mph (47kph) at 2,100 engine rpm. When using a single engine, the top level road speed was 22mph (35kph) with the 1.19 ratio and ~20mph (~32kph) with the 1.37 ratio. The M3A5 was borne out of the dire shortage of tanks which necessitated the installation of the diesel engine in riveted-hull tanks as well as welded-hull vehicles. M3A5 was referred to by the British as Grant II.

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Medium Tank M3A3 Lee^{1-11,23-27,30}

The M3A3 was a welded-hull Lee with the GM 6046 diesel engine; improvements to the power unit listed for the M3A5 appeared on the M3A3 as well. The British called diesel-engined M3A3s Lee V and Continental-engined M3A3s Lee IV. This may only be a paper designation, as no M3A3s were produced with the Continental R975. The British, trying to keep pace with the plethora of tank types emerging from the US, reserved designations for expected production models. Lee IV is apparently just such a designation that was reserved but whose vehicle never saw production.

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Medium Tank M3A4 Lee^{1-11,28-30,33}

The M3A4's A57 power unit was composed of five Chrysler L-head automobile engines geared to run as a single motor, and was devised to help alleviate the expected shortage of tank engines. Each individual engine had its own crankshaft, pistons, camshaft, valves, manifold, carburetor, and distributor. All five engines were assembled to a common crankcase, inside of which each of the five engine crankshafts spun a drive gear which drove a larger gear that was keyed to the power unit driven gear shaft. This shaft drove the engine clutch. The size of this conglomeration required extending the hull of the M3A4, resulting in a distinctive space between the suspension bogies of M3A4s which is about 6" (15cm) longer than that of other M3s. Bulges in the engine compartment floor and roof accommodated the A57's fan and radiator, respectively. No production M3A4s featured side doors on the hull, and other late features like the stronger suspension bogies and three roof ventilators were present. M3A4 was called Lee VI by the British.

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References

1. Hunnicutt, R.P. Sherman: A History of the American Medium Tank. Navato, CA: Presidio Press, 1994. Reprinted with permission from Sherman, R.P. Hunnicutt ©1994, available from Presidio Press, 505B San Martin Drive, Suite 160, Navato, CA 94945.
2. Doyle, David. M3 Lee Grant: The Design, Production and Service of the M3 Lee Medium Tank, the Foundation of America's Tank Industry. Stannington, Northumberland, England: AFV Modeller Publications, 2020.
3. FM 23-81 37-mm Gun, Tank, M6 (Mounted in Tanks). Washington, DC: War Department, 3 April 1942.
4. FM 23-81 C3 37-mm Gun, Tank, M6 (Mounted in Tanks). Washington, DC: War Department, 2 November 1942.
5. FM 23-95 75-mm Tank Gun M2 (Mounted in Medium Tank M3). Washington, DC: War Dept., 4 May 1942.
6. Conference on the 75mm M-2 Tank Gun. Fort Knox, KY: The Armored Force School Gunnery Department, 1942.
7. TM 9-1750H Ordnance Maintenance--Hydraulic Traversing Mechanism (Logansport) for Medium Tank M3 and Modifications. Washington, DC: War Department, 10 April 1943.
8. Chamberlain, Peter, and Chris Ellis. British and American Tanks of World War Two. Frome, England: Cassell & Co., 2000.
9. AGF Board No. 2. Development of Armored Vehicles, volume 1: Tanks. 1947.
10. Miller, David. The Illustrated Directory of Tanks of the World. Osceola, WI: MBI Publishing Co., 2000.
11. Siemers, Cary. "USA's M3, M3A1, M3A2, M3A3, M3A4, M3A5 Medium Tanks." World War II Tanks & Vehicles and Advanced Squad Leader. 25 November 2000. 10 January 2001 <http://www.shadowsfolly.com/WWII/USA/MediumTankM3.htm>.
12. TM 9-750 Ordnance Maintenance--Medium Tanks M3, M3A1, and M3A2. Washington, DC: War Department, 9 May 1942.
13. TM 9-1751 Ordnance Maintenance--Wright Whirlwind Engine Model R975EC-2. Washington, DC: War Department, 28 February 1942.
14. TM 9-1752 Ordnance Maintenance--Auxiliary Generator (Homelite Model HRH-28) for Medium Tanks M3. Washington, DC: War Department, 20 March 1942.
15. Zuljan, Ralph. "M3 Lee." Second World War Armor. 16 March 2000. 10 January 2001 <http://www.onwar.com/tanks/usa/fm3med.htm>. Second World War Armor
16. TM 9-1750 Ordnance Maintenance--Power Train Unit, Three-piece Differential Case, for Medium Tanks, M3, M4, and Modifications. Washington, DC: War Department, 1 March 1942.
17. TM 9-1334 Ordnance Maintenance--Stabilizers. Washington, DC: War Department, 22 December 1943.
18. Catalogue of Standard Ordnance Items, second edition 1944, volume II. Washington, D.C.: Office of the Chief of Ordnance, Technical Division, 1944.
19. FM 30-40 Military Intelligence Identification of United States Armored Vehicles. Washington, DC: War Department, 9 January 1943.
20. Zuljan, Ralph. "M3A1 Lee." Second World War Armor. 16 March 2000. 10 January 2001 <http://www.onwar.com/tanks/usa/fm3a1med.htm>. Second World War Armor
21. TM 9-1750E Ordnance Maintenance--Guiberson Diesel T1400 Engine, Series 3, for Medium Tanks M3 and M4 and Related Gun Motor Carriages. Washington, DC: War Department, 25 September 1942.
22. TM 9-1731 Ordnance Maintenance--Breeze Cartridge Starter for Radial Diesel Engines. Washington, DC: War Department, 25 August 1942.
23. Tank Data, vol. 2. Aberdeen Proving Ground, MD: US Army Ordnance School, July 1958.
24. TM 9-753 Medium Tanks M3A3 and M3A5. Washington, DC: War Department, 16 September 1942.
25. Model 6046 Series 71 Twin 6 Cylinder Diesel Engine Maintenance Manual. First ed. revised. Detroit: Detroit Diesel Engine Division, General Motors Corporation, 1942.
26. TM 9-1750G Ordnance Maintenance--General Motors Twin Diesel 6-71 Power Plant for Medium Tanks M3A3, M3A5, and M4A2. Washington, DC: War Department, 1 September 1942.
27. Zuljan, Ralph. "M3A3 Lee." Second World War Armor. 16 March 2000. 10 January 2001 <http://www.onwar.com/tanks/usa/fm3a3med.htm>. Second World War Armor
28. ---. "M3A4 Lee." Second World War Armor. 16 March 2000. 10 January 2001 <http://www.onwar.com/tanks/usa/fm3a4med.htm>. Second World War Armor
29. TM 9-1750F Ordnance Maintenance--Power Unit for Medium Tanks M3A4 and M4A4. Washington, DC: War Department, 6 April 1943.
30. Sola, Samuel, Vincent Bobkowski, and Kara Crocker. Weapon Mounts for Secondary Armament. Santa Monica, CA: G. O. Noville & Associates, Inc., April 1957.
31. TM 9-1752 Auxiliary Generator (Homelite Model HRH-28) for Medium Tank, M3. Washington, DC: War Department, 4 August 1941.
32. TM 9-1307 Ordnance Maintenance--75-mm Tank Guns M2 and M3 and Mounts M1, M34, and M34A1. Washington, DC: War Department, 22 May 1944.
33. Modern Ordnance Materiel. Metuchen, NJ: Publications Department, Raritan Arsenal, 18 February 1943.

Last updated 6 Dec 2024.
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