Saturday 5 October 2019

The Avenger that Came Too Late

The situation with British tank destroyers during WWII can be described by the Russian saying "the English take a long time to saddle their horses and ride slowly". The best example of this is the story of the Challenger I: the first prototype was ready in the summer of 1942, but mass production only began in March of 1944. Fewer than 200 vehicles of this type were produced before the end of the war. The story of its successor was even sadder. Officially titled the SP 17-pr A.30 or Avenger I, this tank destroyer did not make it in time for the war. Unlike the Challenger I, this was a purpose built tank destroyer. Mistakes made during the design of its predecessor were taken into account, but it was too late. The development took too long.

Fast tank destroyer for Royal Artillery

The idea of motorizing the 17-pounder gun came up shortly after development began. It was no secret that the gun would turn out to be much heavier than its predecessors. Pushing around a three ton gun was no easy task, and so the first ideas of a self propelled chassis were voiced on August 22nd, 1941, three months before work began. One of the ideas was to install it in the American T1 heavy tank (future M6). There were alternative ideas. For instance, installation of the gun into a British tank with a rotating turret. Another proposal was to install it in a casemate on a foreign tank chassis, but work did not progress past discussions.

Draft project of a tank destroyer on the Crusader chassis. The vehicle on a Cromwell chassis was analogous.

By the summer of 1942 it was clear that the artillery needed a mobile platform for the new gun. By that point the development of a tank with this weapon already stated. The first idea was the A.29 heavy tank, which had excellent protection. However, it was known that tank destroyers need to be very mobile. That gave birth to the A.30, later Challenger I. However, the artillery branch needed a tank destroyer, not a tank. The A.30 was an odd tank, but still a tank. In addition, it was very large and too heavy, according to the artillerymen. By the end of June 1942 the first requirements for a tank destroyer were composed. The artillery branch wanted the same A.30 but with thinner armour and a mass of about 26 tons. The Cromwell with a limited traverse angle could be an alternative.

The second proposal was a strange hybrid, consisting of a turretless crusader with a 17-pounder gun on a new mount. This project was shown to the artillery on July 2nd, 1942, but they were not thrilled. The height of this vehicle was comparable with the A.30, the protection was very poor, and the ammunition was stored very high up. The lead tank designer William Robotam was sceptical. He still thought that the A.30 was the optimal tank destroyer.

Achilles IIC, the most numerous British tank destroyer with a 17-pounder gun. This was a GMC M10 with a 17-pounder gun.

The Royal Artillery was in a difficult situation. On one hand, the A.30 was partially satisfactory, but it was still classified as a tank. Therefore, the A.30 belonged to the Royal Armoured Corps. On the other hand, there were projects with a 17-pounder gun on a Cromwell or Valentine/Vanguard chassis. The concept of a tank destroyer with a gun pointing backwards was seriously considered. The Valentine chassis was not a favourite, since it was much slower than the Cromwell. Nevertheless, that is the chassis that was ultimately chosen. On May 24th, 1943, the Royal Artillery was shown the Valentine 17-pounder SP.

There wasn't much of a choice, especially since the artillery had grandiose plans. 1350 tank destroyers were needed in 1943, 450 more in 1944, and 200 in the first half of 1945. Major General Eldridge, the commander of Royal Artillery, understood the risks of a lagging tank destroyer program. As a result, the problem was partially solved via foreign aid. An order for 700 GMC M10s was made in the US. The order was later expanded and 1648 vehicles were shipped in total.

Another option was the GMC T70 or M18. The British received two such vehicles, which received registration numbers S.238462 and S.238463. The War Department reserved a pool of 800 numbers for these vehicles (from S.263894 to S.264693). However, since the 17-pounder gun didn't fit into the M18, these shipments were never made. As for the SPG on a Cromwell chassis, the Royal Artillery came to the conclusion that a new vehicle had to be built using the A.30 concept. It was given the name SP2 (the Archer was SP1).

Same thing but lower

The first draft of the A.30 SP2 was presented by Robotam at a meeting on July 27th, 1943. By the fall a model was constructed, which was met well. However, it was announced that production of the A.30 SP2 will not begin before the second quarter of 1945. Competition began to break out. One of the most important components of the tank destroyer was the turret, which was to be radically different from the Challenger one. The first variant was developed by Stothert & Pitt, the second by Rolls-Royce. The Rolls-Royce design was preferred, under the condition that the gun mount be redesigned.
Dimensions of the SP 17-pr A.30, the official name of this tank destroyer.

The overall concept was ready by the end of December of 1943. According to the requirements, the mass was no more than 30 tons, and the top speed would be 52 kph. The chassis was the same as the Challenger, but the turret was altered. The coaxial machinegun was removed and the turret was now much lower. The overall height of the SP2 would be 2134 mm. This vehicle would not have one of the Challenger's greatest weaknesses: height.

The crew was reduced to 4 men, three of which were housed in the turret. In addition to the reduction of height, the armour was also reduced. The front was 50 mm thick and the sides and rear were 40 mm thick. he rear of the turret received a massive counterweight. Rolls-Royce designers did not include a roof. Like the American tank destroyers, the fighting compartment was open from the top. The concept of the American tank destroyer was largely followed.

SP 17-pr A.30 in travel position.

While development of the SP2 was underway, the Royal Artillery and War Department continued to argue about what kind of vehicle they should buy. The volume of orders was also discussed. The British military liked the SP2 as the faster and more expensive option. On the other hand, the military's wishes had no power over the British industry. The Challenger, let alone the SP2, was in no hurry to enter production. As a result, the SP1 or Archer was built in large amounts. The Achilles IIC was a true saviour in this scenario. The chassis was already finished and just needed to be converted. The result was that the GMC M10 was the standard carrier of the 17-pounder gun by the summer of 1944. While the rearmament program was underway, the artillery branch still held out hope for a domestic tank destroyer.

The fourth Avenger I pilot. This vehicle was built in the summer of 1945.

As the SP2 design was coming to an end, one event changed its look drastically. The production run of the Cromwell was wrapping up. The A.34 or Comet I was going to replace it. The Cromwell and Comet were similar in many ways, but the chassis was different. In addition to a different shape of the hull the running gear now had return rollers. The SP2 had to be furiously changed, both the hull and turret. Experience also showed that in some cases (especially in the city) vehicles were vulnerable to fire from above. SPG crews built their own roofs in the field.

The development of a roof for the SP2 came up in January of 1945. The name of the SP2 also first turned up in January: Avenger I. Unlike cruiser tanks, whose names started with the letter C, tank destroyers had names that started with the letter A. In addition to the aforementioned Avenger, Archer, and Achilles, the SP3 received the name Alecto.

Unlike the Challenger, no coaxial or hull machineguns were installed.

The first Avenger I pilot was delivered in February of 1945. The vehicle received the registration number S.348560. The second pilot, S.348561, was delivered in April. A pool of 500 WD numbers (S.348560-S.349059) was allocated, hinting at the amount of vehicles that would be ordered. However, by the spring of 1945 it was clearly too late. There was no reason to hurry with production. No more than 10 vehicles of this type were delivered in the first 7 months of 1945.

View from the front. The driver's vision port can be seen. It was the source of many complaints, since the visibility decreased.

The final version of the SP 17-pr A.30, as it was called in documents, was radically different from the initial one. The mass grew to 31 tons due to the new chassis (the trials report had an even larger number, 33 tons). To meet the height reduction requirement the turret platform was lowered. The driver's compartment hatches were made from scratch. They were much better than the ones on the Cromwell or Comet.

The low turret was one of the Avenger's advantages. Even with the roof installed the height of the vehicle was only 2.5 meters.

The turret was also radically different from the Challenger. Like originally intended, it was open from the top. Various changes increased the height of the vehicle to 2210 mm, which is still not bad for a tank destroyer. The roof increased that height to 2.5 meters, although it could be removed. The "light" variant of the roof with hatches that could be flipped open was installed on struts, which helped with ventilation. The openings could be covered with a canvas in bad weather. 

The gun mount was also different. The front of the turret was attached with bolts to make servicing the gun easier. The crew position changed. Unlike other British tanks and SPGs, the gunner was to the right of the breech. The gun itself was different from the one used on the Challenger. The 17-pounder Mk.VII had a breech that opened to the left. The turret basket was preserved, which made the crew's life easier but reduced the amount of ammunition on board. Only 55 rounds were stored instead of 70-75. A Bren gun was kept inside to protect the crew from enemy infantry.

Limited release

The third Avenger I pilot was put through trials starting in July of 1945. Trials showed that the increased mass did not radically impact mobility. The top speed was still 56 kph, the average speed on a highway was 43.5 kph and the average speed on a dirt road was 29 kph. The driver's position (especially the seat) was criticized. It was hard to see through the forward observation port. However, it was partially the port's fault: while the Challenger and Cromwell had a very large port, the Avenger I had a much smaller one. Changing gears was also difficult.

View from the back. While the tank destroyer was being designed the chassis changed. Instead of the Cromwell the tank destroyer was built on the Comet chassis.

The vehicle drove for 2426 km on a highway and 2406 on dirt roads. The last 1600 km were the toughest. The SPG started to fall apart. 37 small defects were discovered at this stage. The gearbox had to be replaced at 1984 km. The overall results were satisfactory. Most of the defects were due to production. The fighting compartment and ammunition racks turned out really well. It took 8 seconds to reload the gun on average, which was a normal result.

Light roof sections are open. The roof was introduced due to combat experience where enemy grenades and shell splinters would come flying through the open top.

Rolls-Royce's tank destroyer turned out to be a very good fighting machine: more mobile than the GMC M10 and also lower. This is exactly what the British artillery wanted. The problem was that it was 1.5-2 years too late. By the time the Avenger I was put into production the war was almost over. The role of tank destroyers was filled by the Archer I and Achilles IIC, not to mention the Sherman VC. 

24th production vehicle, 1945. Due to the end of the war the production volume was reduced five fold.

The financial capacity of the treasury was not unlimited, especially due to the debt owed to the US. Plans for production of 500 Avengers were forgotten. According to modern data 80 Avengers were delivered between February 1945 and March 1947 with registration numbers S.348560–S.348639. The bulk of the production was before the spring of 1946.

The Avenger I's career was quiet and very short, like its similarly unfortunate "brother", the Alecto.

The Avenger I was Britain's last cannon-armed tank destroyer to be built in a large series. The post-war fate of the vehicle was short. The tank destroyers were sent to two regiments, one of which was in the BAOR (British Army on the Rhine) in the British occupation zone. These vehicles quietly served until 1949 when they were written off. Not a single sample survives to this day. This is a sad and unfair end for a rather good fighting machine whose only fault can be summarized by the words "too late".

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