Monday 5 June 2023

First Among Equals

The defeat of the British Expeditionary Force in France in 1940 was a wake-up call for British tankers. It was clear that their tanks were not suited for modern war. Light tanks had no chance to survive on a battlefield saturated with anti-tank guns, and even heavier infantry tanks were more vulnerable than expected. The Infantry Tank Mk.I armed only with a machine gun was discarded immediately. The Infantry Tank Mk.II proved itself better, but was still far from perfection. German forces were expected to cross the Channel any minute, and Britain had no modern tanks to repel them with. The only choice was to develop a new tank, and quickly. This tank was called the Infantry Tank Mk.IV or Churchill I.

A tank of compromises

Work on the new tank began in July of 1940. The A20 tank, a potential replacement for the Infantry Tank Mk.II, looked quite archaic compared to its German adversaries. However, the British were not prepared to give up on the concept just yet. Harland & Wolff built one prototype, but there were many issues with it, not the least of which was the insufficiently powerful Meadows DAV engine.

Experimental A20 tank, the Churchill’s predecessor.

The British were in a tough situation when it came to tank engines. The army didn’t want to spend money on engine development, expecting to be able to adapt an engine already in production. This is what happened in this case: the DAV was initially meant to go into the much lighter Cruiser Tank Mk.V. The Vauxhall company proposed their own engine, the Bedford Twin Six, to replace the troublesome Meadows DAV. As the name implies, it was composed of two six-cylinder engines produced by Bedford, a subsidiary of Vauxhall. These engines showed themselves well on trucks. Vauxhall’s proposal was so enticing that they ended up with a contract not just for the engine, but for the entire tank.

As the new engine failed to solve all of the A20’s problems, Vauxhall decided to build an entire new tank, keeping only the overall concept. This was a questionable decision, as Vauxhall had no experience in building tanks, but at least its engineers already had experience with other heavy equipment.

The customer had no strict requirements. It was only specified that the tank had to have a 3-man turret, a top speed of 16 mph (26 kph), an average speed of 12 mph (19 kph). Most importantly, production had to start in 1941, even in small numbers. Reliability was not a factor.

The new vehicle was indexed A22. Its designers expected the armour and armament to exceed that of the A20, but there was a problem with that. The prospective 57 mm 6-pounder gun was definitely more powerful than the 40 mm 2-pounder, but work on a mount for it was behind schedule. By May of 1941 a mount was only in development for the Cruiser Tank Mk.VI, and even that was in such early stages that there was some doubt that it would be ready before the Mk.VI was taken out of production.

The engine of a Churchill tank, Base Borden, Canada. The two halves of the engine are clearly visible.

The development of a gun mount alone did not solve all problems. Mass production of the 6-pounder gun was not expected to start until October of 1941, but the tanks had to be built as soon as possible. Installation of a triple mounting with a 2-pounder, 3” howitzer, and BESA machine gun was also discussed. Since this mounting had yet to be built and tested, the designers went with the tried and true 2-pounder gun with a coaxial BESA machine gun. Since the A22 (by that point it already received the name Infantry Tank Mk.IV) was positioned as a “universal tank”, it also received a 3” howitzer in the hull. A similar solution was already used on the French Char B1 tank, but the British design was a little more progressive. A dedicated gunner aimed the howitzer, and it could be aimed horizontally in a limited sector without turning the entire tank.

As the 3” howitzer was considered a specialist weapon, the British considered it wasteful to equip every tank with one, and so the Infantry Tank Mk.IVA was developed alongside the Infantry Tank Mk.IV. Instead of a howitzer, another BESA machine gun was installed in the hull. These tanks received a slightly different front hull plate.

Churchill I tank, Base Borden, Canada. Just like the French Char B1, it had a gun in the hull as well as a turret and tracks that wrapped around the entire hull.

The armour was expected to withstand fire from a 2-pounder gun at point blank range. Penetration tables for the 20 mm Madsen gun and 0.55” Boys rifle were attached to the requirements document. It was clear that this tank was not designed for frontal assaults on 88 mm AA guns. Of course, this was not too much armour for a heavy infantry tank, but the thickness could not be increased indefinitely. Designers expected armour thicker than 3” (76 mm) to result in excessive weight.

Like many British armoured vehicles at the time, the Infantry Tank Mk.IV had composite armour. A 2.5” (63 mm) layer of armour was attached to a 0.5” (12.7 mm) layer of carbon-manganese steel with bolts, which in turn was bolted on to a mild steel “skin”. This clever method of assembly was necessary to prevent the tank from falling apart under fire, as even a small deformation of the inner plates would result in nuts dislodging. Trials showed that this kind of design could resist a 2-pounder AP shell from 400 yards (365 mm). However, even a hit close to the bolt did not result in its destruction, while a more conventional design resulted in significant deformation causing secondary projectiles when a shell hit within 150 mm of the bolt. Shipbuilding experience had to be called upon to work with rolled armour of this thickness, thankfully Great Britain had no shortage of it.

A column of Churchill II tanks. The driver’s observation port is open. This photo also shows the main difference from the Churchill I tank: a BESA machine gun is installed in the hull instead of a howitzer.

The fighting compartment roof and floor were ¾” (19 mm) thick, the engine compartment roof and floor were ⅝” (16 mm) thick. The driver’s observation port armour was 3.5” (89 mm) thick. The driver could open the port to improve visibility while driving. As soon as the fighting started, he could close it and observe through a bulletproof glass block. If the fire was too heavy, the glass block could be closed up by a shutter, and the driver could continue observation through his periscope. This shutter came in handy even under rifle fire, as bullets ricocheted off the sloped upper front plate and into the driver’s visor. As the periscope was relatively easy to destroy, the shutter was designed to fall off in case of damage, rather than get stuck in place. It was preferable that the driver be vulnerable than blind. The large 9” by 12” observation port flap was designed to stay in place if the hinges were destroyed.

The Infantry Tank Mk.IV had two cutouts made in the driver’s visor plate for the howitzer and its sight, the Mk.IVA had just one cutout. The hull gunner had neither an observation port nor glass block. He could only observe through his periscope or gun sight. Due to the complex shape of the front plate there was an idea to make it cast, but there were no available factories in the UK that could produce it in necessary amounts.

A Churchill II hull. The design was complex, and many cutouts weakened the armour.

The side armour was made from 2.5” (63 mm) thick steel. Large 22” by 15” evacuation hatches were cut out. Like the driver’s vision port, these hatches were supposed to stay shut when their hinges were destroyed. They could still be opened from the inside in this condition to prevent the crew from becoming trapped in their tank. A small pistol port was cut in the center of each escape hatch.

Unlike the A20, which was equipped with an Infantry Tank Mk.II turret, the A22 received a new cast turret. Its prototype was cast by the General Steel Castings company in Chester, Philadelphia, and so the turret was referred to as “American” even though it was produced within the UK. The armour was up to 95 mm thick. There was no commander’s cupola. The commander observed the battlefield through a rotating periscope in his hatch. The turret weighed 6.5 tons fully stowed.

A Churchill I tank that served as a firing range target. Separate cutouts in the front plate for the howitzer and its sight can be seen. The tank behind it is a Black Prince, the last vehicle in the Churchill family. Photo from Yuri Pasholok’s collection.

Brigadier F.F. Worthington, a Canadian liaison officer, had a chance to observe trials of the A22 prototype on May 8th, 1941. In his opinion, growing the armour was the correct decision. Thick armour used on Matilda tanks proved itself well against the Italians in North Africa. The new tank was quicker than its predecessor, easily negotiating slopes, craters, and trenches. The turning radius of the tank changed depending on which gear was engaged. Despite a weight of 38 tons, it was easy to steer. However, the suspension and tracks were so loud that Worthington suggested sending these tanks into battle with an airplane escort to mask the noise so the enemy didn’t hear them too early. The tank’s armament impressed Worthington. He noted that the presence of a howitzer meant that a purpose-made close support tank was unnecessary. Worthington also learned that installation of a 6-pounder gun was planned, although even at this stage it was clear that the protruding tracks would cause issues with a longer weapon. Nevertheless, his report back home ended with a very optimistic appraisal:
“While this tank has not yet been tried in battles, there is every evidence to indicate it will give excellent performance. [Whether] it should be capable of fulfilling the role of a Cruiser tank is a matter of conjecture which time alone can tell”.

Churchill’s sword and shield

The British military had a similar opinion to Worthington’s. Mass production began in the summer of 1941, and the first specimens left the factory in June. These tanks were subjected to all manner of trials.

Churchill I and II turret diagram.

The armour was tested even before the first production tanks were finished. A cast turret was shot up on May 13th. These trials were performed with 2-pounder AP shot and 25-pounder proof shot.

The first shot fired from the 2-pounder gun from 200 yards (183 m) hit the lower part of the turret and resulted in a complete penetration with back-spall within 3” of the breach. A second shot fired from the same distance did not penetrate the armour. Only a bump was found on the inner side. There was no back-spall, but fragments were knocked off the outside. At point-blank range one shell ricocheted, one was lodged in the armour without complete penetration, the third and fourth resulted in through cracks. The fifth shell knocked a 3” by 3” fragment out of the cracked turret and shattered against the opposite side, leaving a 0.5” dent. Two more 2-pounder shots resulted in cracks, but no penetrations. A 25-pounder shot did not penetrate the armour, but the armour was bent inwards by half an inch. With a nominal thickness of 95 mm, the armour thickness in areas of penetration ranged between 91 and 98 mm.

The large evacuation hatches in the sides were not properly sealed from splash.

An almost assembled tank was tested on June 5th. Only a machine gun and the 2-pounder gun sight were missing. The goal of these trials was to evaluate the weak points of the tank.

Firing at the evacuation hatch edges with a Lee-Enfield rifle from 10-25 yards showed that splash could penetrate into the tank. Penetration was more likely as the bullets landed further from the hinges. The cannon and machine gun ports also let through bullets. The pistol port in the turret was not as vulnerable and resisted splash completely.

The tank was then fired upon with a 0.55” Boys anti-tank rifle. Despite 10 hits to the driver’s observation port, it did not jam. The deflectors welded to the sloped front hull plate to prevent ricochet also withstood the trials. Anti-tank rifle bullets could penetrate the tank’s tracks, but could not tear them even if they hit track pins.

The front hull of a Churchill I tank. Special deflector plates were welded onto it to prevent bullets from ricocheting upwards towards the driver’s visor. This photo also shows the separate ports for the howitzer and its sight.

The 2-pounder gun turned out to be much more effective. Two shots to the front hull dented the sloped armour without penetration, but the third shot hit near the upper edge and bent it so badly that the bolts holding it in place were partially destroyed. The report noted that it was desirable to join plates with welding instead of bolts or rivets.

One tank was put through brief trials at the Lulworth proving grounds on July 9th, 1941. This was a short demonstration for senior commanders, but the tank’s abilities were tested nevertheless.

The 3” howitzer was tested first. New smoke shells worked well and thick white smoke covered the battlefield effectively. The smokescreen offered effective cover after 20 seconds and remained up for 75 seconds. The maximum range for this type of shell was about 900 yards (823 m). The 2” bomb thrower mounted in the turret was not as effective. Its maximum range was just 95 yards (87 m) and the smokescreen it formed grew much slower, reaching effectiveness in 30 seconds.

The Churchill’s suspension assembly. This suspension turned out to be unsuitable for firing on the move.

The tank fired three HE shells at maximum gun elevation after smoke trials were completed. The range was measured at 1100-1125 yards (1006-1029 m). The crew proceeded to shut the hatches and fire off three more smoke shells to demonstrate the effectiveness of the ventilation system.

Firing on the move revealed serious issues. The tank’s speed was limited to just 10 mph (16 kph) due to the unrefined state of its components. The tank under trial drove along a relatively flat field at a slow speed, but a suspension travel of only 5” (127 mm) meant that the tank shook violently even in the best conditions. Out of 9 shells fired from 750-1000 yards (685-915 m) while driving towards the target not a single one hit. Results when driving parallel to the target were better: testers counted 6 confirmed hits and one likely hit out of 8 shots. The pistol port was also tested. The crew could effectively hit a target representing an enemy infantryman standing 10 feet (3 m) from the tank.

Churchill II tanks on maneuvers. Even with the mudguards installed, the front tank is covered with a significant amount of mud.

The tank also assaulted an anti-tank trench. 14 HE shells were fired with the goal of destroying its sides and making it traversable, but the Infantry Tank Mk.IV still became stuck during crossing. It was pulled out and another section of the trench was demolished with 200 lbs of TNT, after which the tank could successfully climb over it. A Cruiser Tank Mk.V could not cross that same trench.

A light jog

In early September British tanks were given names instead of indexes. The Infantry Tank Mk.IV with a howitzer in the hull was given the name Churchill I, the Infantry Tank Mk.IVA with a second BESA machine gun became the Churchill II. The new names did not gain traction immediately, and military documents still referred to the tank as the Mk.IV for some time. Winston Churchill joked that the tank was given his name just as its many defects were discovered. The Churchill tank indeed had many defects, and not all of them were linked to the unconventional layout of the armament and brittle armour.

Churchill and Churchill. Sir Winston was quite aware of the mixed reactions towards the vehicle that was named after him.

Let us go back to 1940. Sir Harry Ricardo, the inventor of the engine used in the famous Mark V rhomboid tank, was no longer in the tank business by the start of the Second World War. However, the talented engineer still had many connections, and periodically wrote angry letters to this or that lord, complaining about the state of British tank building. As you can probably guess, his main gripe was the absence of a purpose made tank engine. Ricardo was not a fan of adapting engines from wheeled vehicles or aircraft for use in tanks. In his opinion, it would take as much time to adapt an existing engine as to design a new one. Most of the time in adapting the engine would be spent on working out defects.

Ricardo had plenty of issues with the Churchill as well. Over a year in development the tank grew from 28 tons to 38.5. The new engine solved the problem of weight only partially, as it did nothing to improve the reliability of the running gear. Vauxhall worked hard to improve their tank, but they did not get far. The lifespan of the tracks was estimated at 20 miles (32 km) in the summer and grew only to 50 miles (80 km) by October of 1941. The suspension also suffered. Ricardo suggested getting rid of springs and making the suspension rigid for a tank that was this heavy.

The Bedford Twin Six engine also had its issues. Ricardo had a high opinion of his colleagues from Vauxhall, but it was hard to hide the fact that the company had no experience in tank building. The engine was fragile and unreliable. Ricardo’s company was called upon to correct the situation, but it was too late. The only thing the tank engine guru could suggest at this stage was to decrease the engine power from 300 hp to 250. This proposal was declined. The water and oil cooling systems already drew 50 hp, and any further loss in power would cancel out any advantages this engine had over the Meadows DAV.

A Churchill II on a tank transporter. Its miserly lifespan meant that long journeys had to be made like this, but there were precious few vehicles capable of carrying a 40 ton tank.

The Churchill tank also had plenty of issues with its clutch, transmission, and lubrication system. Design defects were compounded by manufacturing defects. These issues directly impacted the engine lifespan, for instance as of July 20th, 1941, it measured only 9 hours. It was impossible to establish the lifespan of other components as the tank was unable to complete any lengthy trials without constant stops. Swapping out the engine was a lengthy task. It took six days to install a replacement at Farnborough, and there were not enough spare parts to keep the tank running for long.

Another tank building veteran, Sir Albert Stern, also expressed a negative opinion of the Churchill tank, but much more laconically. He stated merely that the “Infantry Tank Mk.IV is unsuitable for battle and overloaded even with a 2-pounder gun”. Lord Hanky, an ally of Ricardo and Stern in the British government, described the Churchill as a “second rate tank” and “a temporary measure at best”. He suggested that these tanks should be stored close to shore so they did not break down on the way to the battlefield in case of an invasion. Hanky claimed that experts estimated it would take at least a year to make the Churchill into a combat capable tank.

The Churchill tank had other critics. For instance, the Director General of Research and Development at the Tank Department called the layout of the tank an attempt to replicate the tanks of WWI rather than build a high speed tank capable of long marches suited for a modern war.

The Churchill was far from an ideal tank, but it could be built in large numbers.

There were even more criticisms of the Churchill II. The armour and top speed of this 38 ton giant were only slightly better than those of the 25 ton Matilda. The new tank weighed 13 tons more with very little to show for it. To be fair, a small note must be made. Lord Hanky represented the interests of a design group with experience dating back to WWI known as Special Vehicle Design Committee (colloquially referred to as The Old Gang), who designed the even heavier TOG I and TOG II tanks. Hanky was not advocating for the replacement of the Churchill with the TOG as much as attempting to raise the standing of SVDC among British tank builders.

The proposal to stop Churchill production received no support. No one argued that the new tank was without serious issues, but the Churchill was the only tank in production that was developed after the start of the war. The second candidate for the role of a universal tank, the future Cromwell, was only in early stages of development. It would take at least 18 months to design a replacement for the Churchill.

Other members of the government saw no irreparable issues with the Churchill tank. Stopping production was considered unacceptable, and a decision was made to send the tanks into service as is. Tankers were warned to treat their tanks with care and avoid excessive speeds to make sure that their Churchills were not worn out before the designers solved their growing pains.

Early Churchill tanks on the move. By late 1941 such a journey was no longer likely to end in a nightmare for repair crews.

The reliability of Churchill tanks gradually improved. A four-day long training exercise codenamed Exercise Bumper was held in September of 1941. This exercise simulated a counterattack on German tank units that successfully landed in Britain, established a foothold, and were now penetrating deeper into the island. Among other units, three armoured divisions and two army tank brigades took part. Tanks were required to make rapid and decisive advances to overtake the enemy spearhead.

The Churchills were not entirely up for this task. Even though the use of the top gear was forbidden, limiting their top speed to 10 mph (16 kph), half of the Churchills ended up requiring repairs during the exercise and 40 tanks out of 54 were in need of repairs by the end. Most of these repairs were relatively minor, and only 11 Churchills were still in the workshops 48 hours after the end of the exercises. On average, each Churchill tank travelled for 150 miles (240 km). This figure was much worse than that of Valentine, Matilda, and Covenanter tanks that also took part in the operation. The other tanks drove for 225 miles (362 km) on average, 1.5 times more than the Churchill.

Two production tanks were put through trials in early December of 1941. The tanks managed to complete a 65 mile (105 km) march on a concrete road without any issues. This feat was repeated the next day. With the ability to use the top gear restored, these tanks gave an average speed of 14 mph (22.5 kph). Fuel economy was recorded at 0.85 mpg (3.3 L per km), which was better than expected. An experimental tank was tested alongside the production models. This tank managed to drive 700 miles (1126 km) without a breakdown. Vauxhall also finished work on new tracks that were estimated to last for 2000 miles (3218 km) of driving.

A Churchill II tank with a fake 3” howitzer instead of a BESA, Bovington Tank Museum. The letter R in the registration number means that the tank was put through a remanufacturing program.

The lifespan of these tanks grew as crew training and production quality improved. By December of 1941 20 out of 22 serious defects were considered solved. The army set a reliability target: each tank had to be able to drive for 60 miles (100 km) per day, six out of seven days of the week. By the end of 1941 this goal was within reach.

The reliability of newly built tanks was promising, but there were still plenty of old tanks around. By November 27th, 1941, the British army had 381 Churchill tanks, 111 of which were already considered unsuitable for combat and needed a major overhaul.

A remanufacturing program was scheduled for early 1942. 50 tanks were scheduled for overhaul by the end of January, and 700 tanks out of 1000 would be ready by March. The Ministry of Supply estimated that the first 300 Churchill tanks would have to remain on the Home Islands as training vehicles, as they could not be made combat capable. Their lifespan could be extended by transporting them on trailers. There were few vehicles in the UK capable of carrying such a weight, but the Americans promised to deliver 300 of their own trailers.

The situation with the Churchill tank more or less stabilized by the end of 1941. The German war machine stalled in the USSR and the threat of a German invasion of the British Isles was gone. There was no longer a reason to hurriedly produce “second rate tanks” and the quality of production began to rise. Even though the Churchill I and II were replaced in production soon after, there were no radical changes to the design of this tank until the end of the Second World War.

  • Documents from the Canadian Military Headquarters, London (1939–1947) RG 24 C 2
  • Documents from the National Archives (Kew)
  • The Canadian Army at War: The Canadians in Britain, 1939–1944 — King's Printer, 1945
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1 comment:

  1. The story of the directorate of tank design is really quite something. Despite being formed in the late 30s, they got bypassed for every project up until Centurion, their first actual complete tank design the government allowed them to do.

    "The Tank Factory" is a great book, covering their work and going over how much infighting between industrial groups, well-connected engineers, and politicians completely dominated tank design for the interwar period and most of WW2 in the UK.