Section Leaders:
Fionn Kelly & Madmatt

The US M3 Medium Tank

By Dan “dano6” Kowaleski

Introduction:

The war in Europe brought about many changes in the way that tank warfare was looked upon. In the US Army, tanks were typically attached to the infantry as support vehicles or they were part of the Calvary. This type of deployment of tanks changed with the development of the US armored force. The main body of tanks would now be part of their own separate organization. These changes in armor organization were brought about by the overwhelming victories achieved by the German “blitzkrieg” tactics and the sudden fall of France to the German mobile warfare tactics. The US Army decided that its new armored force would have to be supplied with the best equipment available, the M2A1 in order to achieve quick victories. The US Army knew that this tank was already outdated even before it went into production, and a new version based upon the M2A1 chassis was designed to replace it. This new tank was the M3 medium tank.  The M3 was based upon the M2A1 chassis with the addition of a 75mm gun to the right sponson. The side-mounted gun was implemented because at the time there was no full traverse turret designed that could hold the 75mm gun. The M3 was the first US designed medium tank to see combat in World War II. In the article below, the different updates and designs that went into the M3, as well as the results of combat for this new vehicle, are presented.

Early Development:

When France fell to the Germans, the British lost most of their armor during the evacuation of Dunkirk. With most of their armor gone, the British sent a tank mission to the US to procure more armored vehicles. The British wanted to have their designs built by US companies, but the US refused to let any design be built that was not approved by the US Army. The British decided to order over 1780 M3 medium tanks with a few design changes. The original design of the M3 changed many times over the summer 1940 before full production of the vehicle went into effect. The original design of the M3 called for a 75mm T6 gun mounted in the upper hull of the M3 similar to the T5E2. This design was changed to incorporate the 75mm gun in a sponson on the right hand side of the tank. This new design was deemed inefficient because of the limited traverse that the sponson mounted 75mm afforded. The US advised that only a limited number of M3’s be produced due to the gun arrangement limitations, but the British need for new tanks in North Africa outweighed the production limits advised by the US. Additionally the design of a full traverse turret that would hold the 75mm gun was still off in the future. The British needed the tanks immediately. The sponson-mounted machine guns at the corners of the M3 were also eliminated, with pistol ports taking their place.

This is the first M3 which was built at the Rock Island Arsenal.

By late 1940, the production drawings for the M3 were almost 90% complete, and by May 5, 1941, test vehicles from the 4 production companies arrived at Aberdeen. The four producers of the M3 were the American Locomotive Company, Detroit Tank Arsenal (Chrysler), Pressed Steel Car Company, and the Pullman Standard Car Company. These manufacturers produced a total of 6,528 M3s and its variants.

Armament: 

The main armament for the M3 was the 75mm gun T7. This gun was derived from the 75mm M1897 that was adopted from the French during World War I. The 75mm T7 was standardized as the 75mm M2. It had a bore length of 86 inches and a muzzle velocity of 1,850 ft./sec. The weapon was not intended as a main anti-tank gun but as an artillery piece. A counter weight was installed on the end of the barrel to balance the gun. The counterweight was not added to the gun mount because the M2 short barreled gun was due to be replaced in the future by the 75mm M3 long-barreled gun and the longer barrel of the M3 gun balanced itself without the need for counterweights. The M3 gun was being designed for the M4 Sherman tank. The M3 gun had a higher muzzle velocity of 2,030 ft./sec. due to the longer barrel.

A late production M3 with the long-barrel M3 75mm gun.

Secondary armament for the M3 was the 37mm M6 gun mounted coaxially with a .30 caliber machine gun in a full traverse turret. The US version of the M3 also had a .30 caliber mg mounted to the commander’s copula.

Armament Performance (Armor Penetration):

The M3 had the ability to penetrate any German tank common during 1942. The German Mk. III had a maximum armor thickness of only 30mm of armor and the German Mk. IV had maximum armor thickness of 50mm

Ammunition: 

All models of the M3 were assigned the same amount of ammunition. However most crews overloaded the ammo storage for their M3s, a common practice in almost every allied tank platoon during World War II. The crews decided the amount of AP and HE for the 75mm gun depending of the mission they were assigned. The assigned amounts of ammo carried are listed in the table below.

Type                             Amount

75mm                                  50

37mm                                137

.45 caliber                       1200

.30 caliber                       9200

Hand grenades                  12

Armor & Protection:

M3

Type:

Turret:              Cast homologous steel

Hull:                  Rolled homologous steel with riveted construction

Thickness and Angle with Vertical: 

Hull Front:            Actual Thickness                              Effective Armor                      

Upper:               2 inches (50 mm) at 30 degrees                      58 mm

Middle:              1.5 inches (38 mm) at 53 degrees                   63 mm

Lower:               2 inches (50mm) at 0 to 45 degrees                50 - 71 mm

Sides:               1.5 inches (38mm) at 0 to 10 degrees              38 mm

Back:                1.5 inches (38mm)

Top:                   0.5 inches

Bottom:             5-1 inches

Turret:

Front:                2 inches (50mm) at 47 degrees                          73 mm

Sides:               2 inches (50mm) at 5 degrees                            50 mm

Rear:                2 inches (50mm) at 5 degrees                             50 mm

Top:                  0.875 inches (22mm)               

Variants Armor:

M3A1:

Type:

Turret:              Cast Homologous Steel

Hull:                  Cast Homologous Steel

Armor Thickness and Angle with Vertical: 

The M3A1 has the same armor thickness as the M3 for all locations. The only difference between the armor on the M3 and the M3A1 was that the upper hull is a one-piece homologous casting with rounded corners.

A M3A1 with the short barreled M2 75mm gun. Notice the one piece cast upper hull.

M3A2 & M3A3:

Type:

Turret:              Cast Homologous Steel

Hull:                  Rolled Homologous Steel with Welded Assembly

Armor Thickness and Angle with Vertical:

The M3A2 has the same armor thickness as the M3 for all locations. The only difference between the armor on the M3 and the M3A2 was that the upper-hull was assembled by welding not by riveting

A M3A2 with the M2 75mm gun. Notice the welded hull construction instead of the riveted construction of the M3.

M3A4 & M3A5:

Type:

Turret:              Cast Homologous

Hull:                  Rolled Homologous with riveted assembly

Armor Thickness and Angle with Vertical: 

All of the above variants have the same armor thickness and hull assembly as the M3; the only difference between the tanks was the use of different engines.

Engine: 

The M3 was equipped with the Wright R975 EC2 air-cooled radial engine rated at 400 hp. The engine was separated from the fighting compartment by a bulkhead. A driveshaft extended from the motor through the bulkhead to the transmission that was located below the driver. Power was transmitted to the two front sprockets through the differential at the front of the tank. Supplies of the Wright radial engine became scarce in 1942 due to the use of this engine in training aircraft and development of a new tank motor was given to General Motors. GM designed a twin diesel motor based on their 6046 truck diesel. The twin 6046’s produced 375hp and proved to be a better engine combination than the Wright radial engine. The torque produced by the diesel engines was far greater at lower RPM than the gas radial engine. The new GM diesel gave the M3A3 and the M3A5 greater mobility at lower RPM and also increased the maximum speed. The US Army also went to Chrysler to design a new tank motor. Chrysler’s design was that of a 30-cylinder multi-bank gas engine, which took 5 of their 6 cylinder engines and geared them together. This motor combination was larger than the normal motors used in the other variants but its performance was satisfactory. Below is a table that describes the engine used and the max speeds for each vehicle.  

Tank                             Engine                          Horsepower                   Max. Speed

M3                             Wright Radial                        400 hp                         24 mph

M3A1                        Wright Radial                        400 hp                         24 mph

M3A2                        Wright Radial                        400 hp                         24 mph

M3A3                    General Motors 6046               375 hp                         30 mph

M3A4                 Chrysler A57 Multi-bank             425 hp                         25 mph

M3A5                    General Motors 6046               375 hp                         30 mph

Suspension: 

The suspension for all M3’s was the vertical volute spring system. This system was taken from lighter vehicles and was beefed-up by using heavier springs. Tracks were either 16 inches wide or were 16.56 inches wide depending on the type of track used on the vehicle. The ground pressures for each model are listed below (based on T48 tracks).

Tank                             Ground Pressure (PSI)

M3                                               12.6

M3A1                                          12.9     

M3A2                                          12.4     

M3A3                                          12.4

M3A4                                          12.1     

M3A5                                          13.1

Miscellaneous Equipment: 

The M3 and all of its variants were supplied with many different pieces of equipment. Each tank was equipped with an SCR-508 radio that was used for communication between tanks in a platoon. The platoon commander’s tank was also equipped with an SCR-506 radio that was used to communicate with HQ. The SCR-508 was located in the left front sponson and the SCR-506 was located in the right rear sponson. Some of the earlier M3s might have been equipped with the SCR-245. Each crewmember was equipped with a set of headphones linked to the tank’s inter-phone network that was part of the radio. Each crewmember in the M3 was able to hear the commands from the tank commander as well as communicate with all of the other crewmembers over the inter-phones that were provided at 5 locations.

Each M3 was also provided with 2 CO2 fire extinguishers, a 10 lb. fixed fire extinguisher and a 4 lb. portable fire extinguisher.

Each M3 was also provided with 1-5 M1928 .45 caliber sub machine guns and 12 hand grenades. The crew armament was used in case the tank had to be abandoned or was close infantry assaulted. If the crew had to abandon the tank, most weapons were usually left behind in the rush to get to safety.

Total Production 

Tank                             Number Produced                      Production Dates

M3                                          4,924                                 Dec 1940 – Aug 1941

M3A1                                        300                                  Jun 1941 – Aug 1942

M3A2                                          12                                  Jan 1942 – Mar 1942

M3A3                                        322                                 Mar 1942 – Dec 1942

M3A4                                        109                                  Jun 1942 – Aug 1942

M3A5                                        591                                 Jan 1942 – Dec 1942

Total Production                6,258

Many of the M3s were shipped to other countries through lend-lease agreements. The chart below shows the amount of M3s that were kept by the US and the amount sent to Great Britain, the Soviet Union and other countries.

Combat in the M3: 

The first M3 “Grants” started to arrive in Gazala, Egypt during February 1942. During this time the front lines had become static and a lull had set in over the battlefield. Both the British and Germans took advantage of this to re-supply their troops with replacements and equipment.

The British began to train their tank crews on the new M3 tank during this time. The 75mm gun gave the British tankers an effective anti-tank weapon with which to deal with the German tanks. The 75mm gun was also able to fire a quite effective high explosive round. Previous British tanks were only equipped with the 2 pounder gun or the 37mm gun, which fired solid armor piercing rounds. The new 75mm gun now gave the British both an effective anti-tank gun and an effective HE suppression gun. Training on the M3 lasted until May 1942. The long training period with little combat resulted in the tank crews becoming very familiar with the M3 while finding all of the problems with the new tank before actually seeing combat.

Problems with the 75mm gun were found almost immediately. The early M3s did not come with the proper fire control equipment: a range scale or an inclinometer. Gunners improvised ranging scales on the elevation wheel of the 75mm gun. Problems with the HE ammo were also found, as supplies of the 75mm HE in Egypt dated back to World War I. The fuses on this ammunition were set up for indirect fire artillery pieces, not direct fire, flat-trajectory guns, and would not burn unless the round hit almost perpendicular to the target. This resulted in many HE rounds to hitting the ground but never exploding. What was needed was a fuse that had a creep mechanism installed that would allow the fuse to fire at a slight impact. The British located some (90,000) French fuses in Syria that utilized the creep mechanism, which were immediately installed on the supplies of 75mm HE ammo.

Another problem with the 75mm gun was found when tested on destroyed German tanks. The AP72 round had a hard time penetrating face-hardened armor at ranges over 500 yards. The AP72 round was a mono-bloc AP round that was designed and manufactured in order to meet ammunition requirements for the M3 in North Africa. The AP72 projectile had many defects due to limited inspection and would typically break apart upon hitting the German face-hardened armor at longer ranges. It was determined that an armored piercing capped projectile was needed. The US was producing the new APCBC (armored piercing capped ballistic capped) AP61 round that would have been effective, but it was not available in North Africa at the time. Major Northy, an Australian ordnance officer, proposed a solution to the ammunition situation. He suggested using captured German 75mm APCBC projectiles and modifying them to fit the American AP72 casings. The conversion worked very well with a small amount of machining to the projectile. The new round was designated the AP composite and performed equally as well as the new US AP61 round. About 17,000 of these rounds were converted and supplied to the M3 tank divisions.

By May of 1942, the crews of the M3s had plenty of time to train and become combat effective in their new vehicles. Many problems had been solved and the new M3s were ready for combat. The 75mm gun gave the M3 the ability to destroy German tanks at ranges they were not used to, and easily penetrated the Pz. IIIs front armor. This gave the Germans quite a surprise upon the initial engagement. 167 of the new M3s were split between to two British tank divisions, the 1^st and the 7^th. The 7^th British tank division was the first to see combat in the M3.

On the 27^th of May 1942, the 4^th brigade, 3^rd RTR of the 7^th armored division clashed with German tanks outside of Bir Hacheim. The M3s engaged a numerically superior force at 1000 yards and destroyed many of the German tanks. The 3^rd RTR started the engagement with 19 M3s and ended the day with only 5 M3s surviving. The 8^th Hussars also engaged the Germans on the same day. They destroyed 30 German tanks with the loss of 22 M3s. The M3 proved itself quite battle-worthy on its first day of combat. The British destroyed more German tanks than they lost.

A M3 Grant passing a burning German tank in the desert. The destroyed German tank appears to be a Panzer I.

The new 75mm gun was able to engage the Pz. III and Pz. IV(75mm L24 gun) at a range of 1000 yards, while neither of the German tanks could penetrate the M3s front armor at this range. This gave the British the advantage in firepower for the first time. The 75mm gun could also effectively engage heavy German anti-tank guns with HE ammo.

The first US crews to see action in the M3 were assigned to the 8^th British armored division. They saw combat with the 1^st RTR on June 11, 1942 in the area of Tobruk. After 3 days of fighting the three US crews claimed 9 kills on German tanks without a loss. After this action, the crews flew back to the US in order to assist in training tank crews being prepared for combat.

Here a some M3s of the US 1st Armored division moving near Kasserine on February 20, 1943.

The M3 saw action in North Africa with more US tankers starting in the middle of November 1942. The US 13^th armored regiment, equipped with M3s supported attacks in Tunisia until fighting in that area ended. The 13^th armored regiment saw much action in the Kasserine Pass area during February 1943. The 3^rd battalion of the 13^th armored regiment fought alongside the remaining Shermans from the decimated CCA (Combat Command A) and CCC (Combat Command C) along with CCB (Combat Command B) of the 1^st armored division. This combined force fought a withdrawing defensive battle, which decimated the German offensive and forced Rommel to pull his forces back on the defensive, ending the battle. In April 1943, the M3 was pulled back to second line duty and was given a limited standard designation. The M3 was declared obsolete in 1944 and pulled from service.

References:

Hunnicutt, R.P., “Sherman: A History of the American Medium Tank”. Presidio Press, Novato, CA 1994.