Leading to the M10 TANK DESTROYER
Development and use in United States and British Commonwealth Service
By Richard Henry
Date: 24 March 2021
Words: 3 697
A NEW WAY OF FIGHTING
When the Second World War, 1939 -1945 started, the German armoured forces, consisting of tanks, armoured cars and half-tracks brushed aside any opposition with impunity. The Blitzkrieg tactics ensured the rapid defeat of the Polish, Belgium and especially the French army by June 1940.
The neutral United States of America although morally supporting the British and French, looked on with horror at how easily the German tanks crushed the European nations. American military men could see that they might get involved in the war and that they lacked sufficient quantity and quality of armoured vehicles. Their response was at first slow, but just as a snow ball gathers momentum so did the United States industry. The US armoured force was formed in July 1940. Each armoured division would be theoretically equipped with 368 tanks. During the Second World War, the organisation and structure of an armoured division was changed many times.
THE AMERICAN INITIAL RESPONSE
In August 1941, the American Anti-Tank Planning Board laid an ambitious plan for up to 220 anti-tank battalions. The first nine units formed had 37mm M6 anti- tank guns towed by jeeps and 75 mm guns mounted on M3 Gun Motor Carriages (half-tracks). The new tactic was to hold anti-tank guns in reserve and move them rapidly to the point of the enemy (German) armour attack. From the end of November 1941, the psychologically powerful term ‘Tank Destroyer Battalions’ was used for mobile anti-tank guns units. Their stated purpose was to “destroy hostile tanks” in an aggressive, offensive spirit from a defensive ambush position. At first they used stop gap equipment while the various arms of the army tried to hastily design and manufacture a reliable, fast, effective tank destroyer. Various senior officers saw different requirements and doctrines for tank destroyers. Was the best anti-tank weapon an anti-tank gun or another tank? The American War Department decided that tanks should be countered by fast moving, high velocity guns, used en masse.
HANG ON CHAPS
In Europe and later in North Africa, the British and Commonwealth forces fought for survival, confronting the Germans with whatever equipment was available. Their high velocity 2 Pounder anti-tank gun, which entered service in 1936, fired an armour-piercing solid shot which was able to penetrate 37 mm of armour at 450 m range. This was sufficient to destroy German tanks up to the Panzerkampfwagen III. These anti-tank guns were sometimes supplemented by the 25 Pounder Field Gun used in the anti-tank role. The 2 Pounders were reasonably effective but lacked an effective armour protection for the gun crews. The doctrine called for gun pits to be dug but these took time and to dig; even when the spade work was enthusiastic. Originally anti-tank units were essentially a defensive force of towed guns, which it was hoped would be able to fight off or destroy a force of attacking enemy armour. The 6 Pounder still had to be introduced into service.
THE TANK DESTOYER FORCE
Initially the Tank Destroyer Centre was situated at Fort Meade in Maryland. In November 1941 it was moved to Camp Hood in Texas. The tank destroyer force resisted all attempts throughout the war to incorporate it into the armoured force. It grew in numbers and by late 1942 had 100 000 men and 80 active battalions with 64 more battalions planned, reaching its maximum of 106 battalions in early 1943. From October 1943 there was a decline in numbers as the American Army realised that they were unlikely to face a massed German armoured force as was the case in Europe in 1940. Thirty-five of the 106 battalions never left the United States. Of the remaining battalions, more than half saw combat service.
The first tank destroyers approved for production was the M3 Gun Motor Carriage (GMC). This used an American built 75 mm Model 1897 A4 gun (a copy of the French WW1 gun) mounted on the chassis of the M3 Half-track. The chassis was built by the Autocar Company. A total of 2 203 M3 GMC’s were produced. It carried a total of 59 cartridges. In the anti-tank role the M61 armour-piercing projectile could penetrate up to 76 mm of armour at 900 m. After the introduction of the M10 Tank Destroyer, 1 361 M3 GMC’s were converted back into M3A1 Half-tracks.
THE TANK DESTOYER BATTALLION COMPOSISTION
Each tank destroyer battalion consisted of about 800 men. Approximately half the battalions were equipped with self-propelled guns and the other half with towed guns. The towed guns were cheaper and easier to manufacture.
Each battalion was organised into three companies. Initially there were supporting reconnaissance troops, 108 protection troops and eighteen anti-aircraft guns in each battalion, but in January 1943, these forces were found unnecessary and were dropped.
For the self-propelled gun battalions; each of the three companies was equipped with twelve guns. These were four 37 mm self-propelled (SP) guns (which were quickly obsolete) and eight 75 mm SP guns. Each tank destroyer battalion therefore had twenty-four M3 75 mm GMC’s.
These were later replaced by the M10 Tank Destroyer with its 3-inch (76 mm) gun. The towed guns were initially twelve 37 mm guns. The fighting doctrine was for the self-propelled guns to move quickly into ambush positions, fire at the attacking enemy armour with their 75 mm guns and quickly retreat to another defensive position. The SP guns were designed to be fast and manoeuvrable but lightly armoured. They were unable to survive hits from enemy armour piercing rounds but were protected against small arms fire. A secondary role for the tank destroyers was indirect fire support of the infantry and artillery.
COMBAT USE OF THE INITIAL TANK DESTOYERS
The 601 Battalion, equipped with thirty –six, 75 mm M1897 A4 guns mounted on M3 Gun Motor Carriages was the first and last to be used in the envisaged tank destroyer role. On 23 March 1943 during the Tunisian Campaign, the tank destroyers of 601 Battalion destroyed 30 tanks of the German 10 Panzer Division. Flaws in the M3 GMC became evident – too slow, with a high silhouette and the 75 mm gun just capable of destroying the Panzerkampfwagen IV armour.
THE DEVELOPMENT OF THE 3-INCH GUN MOTOR CARRIAGE M10
In November 1941, the Tank Destroyer Board noted the deficiencies of the M3 GMC and dropped the self-propelled, limited traverse gun idea. They then requested a vehicle with a good speed and with a gun in a fully rotating turret with a lower silhouette. The chassis of the early production M4 A2 General Sherman tank was chosen as the drive train. The chosen gun was the 3-inch M7 gun in a cast, pentagonal shaped, manually traversed open-topped turret. The sides of the turret were angled inwards at 15 degrees and had 25 mm thick armour while the partial roof covering was 19 mm thick.
The heavy, M7 Gun of mass 903 kg made turret unbalanced and made for difficult turret traverse. This was eventually rectified by the addition of duckbill weights at the rear of the turret.
Because of the M10’s envisaged role, the armour protection was generally light. The two parts which would normally face the enemy were the thickest. The glacis plate, had 38 mm of armour angled at 55 degrees, the gun mantlet -57 mm. The side and rear of the hull had only 19mm of armour while the engine decking only 9.5 m.
The roof was left open to save mass and allow a wider field of view to spot the enemy. It also allowed for quicker ammunition stowage, emergency escape and better communications with the infantry on the ground.
The prototype of the M10 was designed in early 1942 and the first vehicle delivered to the army in April 1942. After some changes and improvements, the final design was completed by June 1942 and was called the M10 GMC. It was a diesel driven.
Fisher Body Division of General Motors, situated at Grand Blanc, Michigan, USA, were given the initial contract to manufacture M10s. Production started in September 1942. Problems were encountered with the balance of the turret when on a slight sloped ground which prevented the traversing of the turret. Fisher by adding a wedge shaped counterweight of 1 680 kg to the rear of the turret from end of January 1943. This was later reduced to a 1 135 kg (duck-bill) counterweight.
The Fisher manufactured M10s were powered by the General Motors 6046 diesel engine. This was in fact two Detroit 6.71 litre, in- line engines mated to a common crankshaft. The power output from this twin engine was 280 Kw at 2 100 rpm. The advantage of having a twin engine was that if one was damaged, it could be disconnected from the crankshaft and the tank destroyer driven on the remaining engine. The mass of the twin engines was at a heavy 2 204 kg , and along with the duck bill counterweight pushed the combat mass of M10 up to nearly 30 000 kg. This extra mass reduced the maximum on a good road to 48 km/h. By December 1943 Fisher had made a total of 4 993 M10s.
To increase production, the Ford Motor Company was awarded a contract from October 1942 to produce petrol driven M10A1 version using their GAA, 8-cylinder, 335 Kw petrol engine. Ford produced 1 038 M10A1s up until September 1943.
ARMAMENT, SIGHTING and AMMUNITION
The M7 Gun had a calibre of three inches (76.2 mm). It was in an M 5 mount. The barrel was long and heavy and caused balance and traverse problems. The gun had only a marginally better anti-tank performance than the 75 mm General Sherman tank. When the Germans introduced their Tiger and Panther tanks it was found the most armour piercing rounds were ineffective against the new German tanks frontal armour but still effective against the side armour. The lighter M1 gun fitted in the later 76 mm Sherman tanks, fired the same projectiles but had a different cartridge case. The 76 mm Sherman gun was found to be superior anti-tank gun than the M7 Gun but also not able to penetrate the frontal armour of the Tiger and Panther tanks. This lead to the American Army introducing a new 90 mm M36 Tank Destroyer into service . The British fitted their Ordnance Quick Firing 17 pounder Mk V anti-tank gun in the M10s to become known as the “Achilles”
Initially both the M10 and M10A1 had fire controls limited to a direct fire model M51 or M70 G telescope, .as the main perceived target was enemy armour. As the main role of the M10 changed to indirect fire support, an azimuth indicator and gunners quadrant was introduced as from May 1943. An M12A4 panoramic telescope was installed on the right side of the turret for this purpose. In December 1943 the Tank Destroyer Battalions in Italy were firing a collective 15 000 high explosive shells per month and very few armour-piercing rounds as German tank were few and or not engaging the Americans. There was heavy anti-tank action around the Anzio Landings when the Americans tried to outflank the German Gustav Line in January 1944.
Fifty-four rounds of 3 inch ammunition were carried in the M10. Forty eight rounds were stored in four racks in the hull sponson. For immediate use six rounds were kept ready at the rear of the turret.
The 3- inch M7 could fire five types of ammunition: The 3-inch Mark II, M2 cartridge case for each of the projectiles was the same. It was 585 mm long (longer than the case for the 76 mm Sherman). The case contained a propelling charge of 2.21 kg of M1 class powder. One of the Manufacturers of this ammunition was Maxims Munitions Company (MMC)
M79 Armour Piercing Tracer Shot. This solid steel projectile was fired at a muzzle velocity of about 850 m/sec. The tracer element at the rear of the shot burned and indicated the trajectory and land of the shot. It could penetrate up to 92 mm of armour, sloped at 30 degrees from the vertical at a range of 914 m.
The M62/M62A1 Armour Piercing Capped Ballistic Capped / High Explosive Shell with Tracer. This had a mass of 7 kg which left the barrel at 792 m/sec. It had a sharply pointed projectile with a cap which facilitated penetration of the armour plate before the shell exploded. It could penetrate 88 mm of armour at a 30 degree slope to the vertical at a range of 914 m. The land of the shell was also indicated by the burning tracer element. This projectile was superior to the one fired by the German Panzer IV.
The M42A1 High Explosive shell had a mass of 5.84 kg. It was filled with either 390 grams of TNT (Trinitrotoluene) or a 50/50 mix of Amatol and TNT. The shell was fused with an M48 impact fuse. It was fired at a muzzle velocity of 853 m/sec. and was used for indirect artillery fire or against fortifications and soft targets like infantry in trenches or antitank guns. The light shell and small explosive charge made it ineffectual against most enemy targets. The maximum range was about 14 700 m.
M88 HC B1 smoke shell was used in small numbers to lay down a smoke screen. This hid the retreat of the M10s or the supporting infantry and prevented them from being over-run by the enemy.
T4 High Velocity Armour-Piercing with Tracer Shot was issued from September 1944. This shot had a sub-calibre tungsten carbide penetrator which was within a steel jacket. It also had a wind shield to prevent the projectile velocity decreasing too much. They were issued to units in small numbers to defeat the Panther and Tiger tanks. It was capable of penetrating 135 mm of armour at 30 degrees to the vertical at 914 m and 150 mm at 500 m. By March 1945 about 10 400 of these rounds had been delivered to the European theatre.
Added to the above ammunition for the M7 gun the flowing was also carried:
450 Rounds of .30 calibre ammunition for the crews M1 carbines
300 Rounds of .50 calibre (12.7 x 99 mm) ammunition for the anti-aircraft M2 Browning Heavy Machine Gun. These were stored in six boxes of 50 rounds each on the floor of the vehicle.
6 Smoke Grenades
6 Fragmentation grenades
CREW AND FIGHTING COMPARTMENT LAYOUT
The crew of the M10 Tank destroyer consisted of five men. The commander (often a sergeant) sat on a folding seat to the right rear of the turret. The gunner stood or sat on the left side of the gun, and aimed the gun using the direct fire M51 telescope. He had to use the slow hand traversing wheel to turn the main gun onto target. The gun loader stood to the right rear right of the gun able to quickly load one of the six ready rounds at the turret rear. The driver, sat behind the glacis plate on the front left of the M10. His vision was through a periscope through the glacis plate when in combat. He was responsible for driving the M10 and listening to his commanders instructions. The co-driver also shared some of the driving duties but was mainly responsible for operating the radio and undertaking the required vehicle maintenance at halts and over-night stops. He also ran the vehicle engine during halts to charge the vehicle’s batteries. Crews were very reliant on each man performing his duties quickly and efficiently and crews were very close as their lives depended on it.
The open topped turret made the crews vulnerability to mortar fire, small arms fire, hand grenades, and shrapnel from air burst artillery fire. Exposure to wind, rain, snow and freezing temperatures also made operations difficult, and crews covered the turret with tarpaulins to improve their comfort and their operational effectiveness.
For large maintenance tasks, such as removing a track link, the crews often had to use the pioneer tools such as axe, crowbar sledgehammer situated at the rear of the vehicle. More routine adjusting the tension of the tracks was done by a large 3- inch (76.2 mm) spanner.
For personal protection the crews had M1 Carbines or Thompson sub machine guns. The commander may also have had a .45 Colt Pistol. Alongside the co-driver was space for a M1903 .30 Calibre Springfield rifle with an adaptor for anti-tank rifle grenades.
BRIEF HISTORY OF M10 COMBAT USE
North Africa and Italy
After the North African campaign the tank destroyer battalions were re-equipped with M10 tank Destroyers and were part of the force which landed at Salerno, Sicily in September 1943. In January 1944, during the Anzio Landings when the American 5 Army tried to outflank the German Gustav Line Defensive, the M10s saw severe action against German armour. Sporadic actions continued until the Germans withdrew from the Gustav Line in May 1944. On 29 February for example, the M10s were accredited with knocking out 25 tanks and Stug Assault guns. After the breakthrough the M10s fought up the mainland of Italy not however in the envisaged role. The Italian terrain was not conducive to large scale tank battles. The German forces were mostly deployed in a defensive role and their limited number of tanks covered mountain passes and strategic points. Later the M10s were mostly used for fire support.
North West Europe
The largest deployment of M10 and M10A1 tank destroyer units was in this theatre, starting with the D-Day Landings of 6 June 1944 where 30 tank destroyer battalions were deployed. Initially there was little tank fighting. Infantry Division commander soon however requested a battalion of M10s in support. These were used as direct fire support and later indirect fire support (as well as and moral support to the infantry). A company of M10s was often allocated to an infantry regiment. The doctrine of using the M10s in numbers against a large German armoured force was forgotten. When the M10s later encountered Panther and Tiger tanks they realised that they were unable to penetrate their frontal armour. As a stopgap the T4 High Velocity Armour-Piercing with Tracer Shot was issued from September 1944. At the same time some M10s battalions had one company equipped with up-gunned 90 mm M36 Tank Destroyer. The M10 however saw combat until the end of the war. During the Battle of the Bulge, M10s were used in a role closer to their doctrine. From reserve positions they were moved to the point of attack where they ambushed the German tanks. In this role they were an essential part of the American defence of the Ardennes.
Once the US Army had been equipped with M10 Tank Destroyers, other Allied armies were supplied with them. The Free French were the first to receive 155 M10s them under the Lend Lease and a 100 later on. The British received the first of a batch of 1 128 vehicles in late 1943 and a further 520 in 1945 as part of the Lend Lease scheme. Of the 1 654 M10s delivered to the British (Commonwealth Forces), 1 017 were up-gunned with the British potent Ordnance Quick Firing 17 pounder Mk V anti-tank gun at the Royal Ordnance Factory at Leeds. Works was started in May 1944 and completed in April 1945. With this modification the vehicle was officially called the M10 c. They were also known as the 17 pounder S.P Achilles Mark 1 c or mark 11 c”. With this gun the British forces were able to knock out Panther and Tiger tanks. The South Africans were one of the first to received M10s in late 1943 and early 1944 but did not received any of the up-gunned variety. See part two of this article for these details.
Official US Army name: 3-inch Gun Motor Carriage M10
US Soldiers name: TD (Tank Destroyer)
British name: 3-inch Self Propelled Gun
British name for up-gunned version: M10 I c or M10 II c “Achilles”
Canadian name, possible post war name: Wolverine
South African name: M10 Grouse
THE END OF THE WAR
A US Army study found that 39 of the tank destroyer battalions each destroyed on average 34 tanks, 17 towed guns and 16 pillboxes. On the 10 November 1945, the Tank Destroyer Centre was closed and the last battalion was deactivated in 1946.
After the Second World War, with the American deactivating their last battalion in 1946, many M10s were scrapped. They did however supply a small number to Italy. Quite a few European countries such as Belgium, Denmark and the Netherlands received 17 Pr M10c‘s from Britain. Other countries such as Israel and the Republic of China acquired M10 by other means.
The war had shown that the requirement for tank destroyers to be used en masse to stop enemy tanks was not a sound doctrine. The lightly armoured tank destroyers with their open top were less effective at fighting German tanks than the better armed and armoured tank. A large number were made available as Lend Lease equipment and some were up-gunned with British 17 Pr anti-tank guns to become the S.P Achilles. See part two for South African use of the M10 Tank Destroyer.
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