United Kingdom (1943)

Assault tank – 2 built

Earlier projects

As early as 1941, there were concerns about the A22 Churchill tank. Its performance had been unsatisfactory, due mostly to its mechanical unreliability and poor speed. This lead to several mock-ups and designs, which were part of a project known as the “Cromwell Rationalization Programme”. These used the A27 Cromwell chassis and automotive components as a basis for future vehicles. Projects were drawn up by the Rolls Royce Tank Development Department and by English Electric. These projects, among others, led to a series of infantry and heavy tanks. As a whole, they represented a great example of the rapid escalation of requirements, particularly notable is the increase in armor protection and weight, given the short time frame between the A.28 design and A.33 prototype between late 1941 and early 1943.



The A.28 Infantry Tank, the initial design, was essentially an uparmored A.27 Cromwell with large broad skirt plates covering the sides.

The armor layout of the A.28 was different from the initial set of A.27 Cromwell specifications. The tank featured 3 inches (76.2mm) of armor protection on the frontal vertical plate and 3.5 inches on the driver’s visor plate. The side armor configuration of the A.28, like that of the A.27, consisted of two plates with the Cromwell-type Christie suspension in between them. In the case of the A.28 the design called for a slight reduction of the thickness of the outermost plate, which was supplemented by thick armored side skirts. The thicknesses of various parts of the armor were reduced in an attempt to keep weight down, reducing roof armor, hull floor armor and rear armor. In total, the A.28 was expected to weigh 28 tons.



This A.34 Comet tank, which is under restoration, shows the suspension and both layers of armor visible. The outer side armor is bolted to the inner side armor and the suspension brackets. The A.28, A.31 and A.32 would likely have a similar design – Source: hmvf.co.uk

Side armor protection consisted of a 1.875” inch (47.6mm) thick skirt, a 1.062” inch (27 mm) outer plate, and 0.562 inch(14.3mm) inner plate. This brought the total combined thickness of the side armor to 3.5 inches(88.9mm). While the maximum thickness of the frontal armor increased from 3 inch to 3.5 inches. (76.2mm to 88.9mm) this was not considered a sufficient increase in protection. It is very likely that the meagre increase in armor protection over the Cromwell played a role in the demise of the A.28. The project was canceled in December of 1941 and its design never left the paper and blueprint stage.

This was soon followed by the A.31 Infantry Cromwell, the description stated that it “was the heaviest vehicle which could be carried on a standard Christie suspension of 5 wheels per side”. Compared to the A.28, the overall armor thickness of the A.31 increased. The armor layout is described with most of its protection being along its front and side arc. The turret protection would have been a respectable 4.5 inch(114mm) front, with 3.5 (88.9mm) inches on the sides and 3.25 inches(82.6mm) at the rear. Hull protection was a 4 inch (101.2mm) front visor plate, with 2.312 inches (58.7mm) side armor, and 1.5 inches (38.1mm) of armor along its rear. There is no explicit mention of side skirt plates, however it is possible that this is a combined armor total, given its suspension configuration would be otherwise identical to A.27 and A.28. It had an estimated weight of 32 tons. This project also never left the paper and blueprint stage.

A competing design, the A.32 Infantry Cromwell would have featured a modified Christie-type suspension “using straddle mounted pivot shaft bearings” which was also reserved for a future tank “A.35”, which was a proposed heavy version of A.34 Comet. This suspension was likely designed to cope with the increasing weight requirement. Another feature of the design were the 19 inch (482.6mm) wide tracks, significantly wider than the 14 inch (355.6mm) tracks that were considered standard on the early-type Cromwells and on the aforementioned tanks, A.27, A.28 and A.31. Compared to the A.31, the A.32 appeared to eschew frontal protection for all-around protection, with its turret armor being 4 inches thick in the front, with 3.5 inch thick sides and rear. Hull protection was 3.5 inches on the driver’s visor plate, 3 inches combined side armor and 2 inches to the rear. It was a heavier tank at 34.5 tons and it too never left paper and blueprint stage.

The A.33

The original design for the A.33 was meant to produce a “Heavy Assault Tank based on the Cromwell using thicker armor and redesigned suspension”, “re-introducing armored skirting plates over the suspension”. The project appeared to be directly challenging the Churchill tank, as several mentions are made of the automotive unreliability, poor speed, and overall negative opinion of the Churchill. The A.33’s project goals and requirements were mirrored in the T14 Heavy/Assault Tank, a tank which was designed and built in the United States.

The question of what an “Assault Tank” amounts to is a guessing game, particularly when compared to Nuffield Ltd’s ‘Assault Tank’ entries (which ultimately led to the A.39 Tortoise). The T14 and A.33 both resemble conventional infantry tanks, however they had more mobility and speed than anything in the class prior. Does the increase in mobility alone remove both tanks from the category of infantry tanks, simply because of this? Even official documentation appears confused (and rightfully so) about what the exact nature of and role that an assault tank would fill.

English Electric built the two prototypes. The most early variant of the tank, produced in 1943, was known interchangeably as the “A.33/1” or “A.33/A” and used American horizontal volute suspension and tracks found on the T1 (M6) heavy tank, known internally as “T1E2-type” suspension. This was used as a stopgap as the UK was developing their own heavy bogie-style suspension.



The A.33/1 with it’s T1E2 (M6) heavy tank-type tracks and suspension. It also has a mount for the twin Vickers “ K” machine-guns on the roof.

The later “A.33/2” or ‘“A.33/B”, did not use a widened or strengthened Cromwell suspension but rather a UK designed suspension known as the “R.L.-type suspension” (short for Rolls-Royce and L.M.S. Railway) which was a bogie type similar to the aforementioned American suspension but with significantly longer suspension travel, which was intended to provide improved ride quality and cross country mobility. The UK-type suspension turned out to be expensive, complicated to produce and had reliability problems during trials.

Both A.33 types were powered by an uprated version of the existing Meteor engine. This was the same engine that powered the A.27 Cromwell, with fairly minor alterations. This version produced 620 hp at 2550 rpm. A similar but modified version of the Merrit-Brown transmission from the Cromwell was used in the A.33, which had 5 forward gears and 1 reverse gear. A top speed of 24.8 mph (39.9 km/h) forward and 1.45 mph (2.3 km/h) in reverse gave the tank a significant increase in top speed over the Churchill, which it was directly competing with.



The A.33 in foreground with A.38 Valiant in the background.

The entire tank was of an all-welded construction, uniquely featuring large side access doors on both sides of the hull and broad skirt plates that covered much of the sides of the tank. The A.33 was protected by 4.5 inches (114mm) of vertical armor on both the turret and hull faces. The turret sides were 3.5 inches (88.9mm) thick and the rear was 3 inches (76.2mm) thick. The hull sides were 2 inches (51mm) thick along the fighting compartment. The hull sides along the engine deck were 1.5 inches (38.1mm) thick, and the rear hull armor was 3 inches(76.2mm) thick. The A.33/1 had a 1 inch thick welded-on appliqué plate intended to cover the gap above the track skirts, running horizontally from the front plate to the engine compartment. This was not necessary on the A.33/2 as the track skirt plates covered the entire side hull. The aforementioned skirt plates were 1 inch (25.4mm) thick skirt, and featured 3” thick side escape hatches,which connected to tank’s fighting compartment on either side by 1 inch thick cast armored tubes. This was a considerable amount of all-around protection, with no less than 3 inches of armor on any face of the tank.



The 4½ inch (114mm) thick frontal armor visible through the driver’s hatch.

Initially, the tanks were intended to be armed with the then standard 6 Pounder. The requirement was later changed to the 75mm QF Mk V, very likely to match the standard armament of the Cromwell at that time, with both prototypes being armed with the 75mm gun. It is often said that the initial prototype (A.33/1) was armed with the 6 Pounder, but it appears that this is not the case as all relevant information only makes mention of the 75mm gun, although the two guns were reasonably interchangeable. The main gun has 10 degrees of depression and 20 degrees of elevation. The A.33 carried 80 rounds of either 57mm or 75mm, 5000 rounds of 7.92mm in belts for it’s Besa hull and coaxial machineguns, 30 rounds for its smoke-launching mortar, and 2000 rounds of .303 (in drums) for the roof mounted twin Vickers ‘K’ guns, intended for anti-aircraft duty.



The QF 75mm Mk. V gun with muzzle brake and Besa, coaxially mounted. Some photos show the hull MG being plated over, although all documentation does make it clear that they fully intended to mount a 7.92 Besa if the vehicle were to reach production.

First Drive

On the 11th of November 1943, the tank was given an acceptance trial by English Electric. The full battle weight was 40 tons, 8 cwts (896 lbs). It wasn’t stowed with all ammunition and equipment but was fitted with weights to represent the missing equipment. A number of minor defects were noted during the 1000 mile trial. The test track was described as ‘rainy and muddy’ and ‘tough going’.

Oil leaks were noted at 442, 704 and 728 miles respectively. This was apparently from a mixture of the cold weather and cold engine causing oil valves and oil filter connectors to come loose. This was stated to be likely a side effect of distortion of piping. A rubber seal was suggested to resolve the problem. Once the engine was ‘warmed up’ the leaks appeared to stop.

At 600 miles, a hydraulic pipe connected to the transmission clutch leaked. It was being rubbed by the oil tank balance pipe and had chafed through. At 556 and 600 miles the engine would not switch off- the electrical earth leads to the magnetos were not making contact. It was reported that this was a common issue with other Cromwell tanks and not exclusively a problem to A.33.

At several points in time, the driver was unable to put the tank into 2nd or 3rd gear due to a pin on the gear-control lever having come loose. This pin was originally press fit into place, but at 750 miles the pin was brazed into position in an attempt to alleviate the problem. It was suggested that, in future, if production was to occur, the pin would be welded into position.

The brakes were adjusted at 442 miles, but after an additional 15 miles traveled the steering brakes were binding and this forced the tank to stop. It appeared that the brakes were over-adjusted. Once corrected, the tank functioned, but needed one additional adjustment at 853. The trial noted that the brakes were damaged, cracked with leading edges burned, but, noted as still “serviceable”.

Trouble with the American-made T1 suspension was noted. Track guides kept coming loose, guide lugs constantly required tightening during the first 300 miles. It was noted that after this preliminary problem, the issue did not persist. No track links were removed in the 1000 miles running and over 50% of the possible track adjustments had been used, due to the rubber bogies. Minor issues were noted with the sprocket ring. Its bolts incorporated a “shakeproof washer” which could not handle the vibration of the tank on maneuver and they were replaced by normal “tab” washers. Sometime during the end of the trial it was noted that several of the suspension bogies had lost their inner bearings, having no apparent effect on ride quality.

The hull’s skirt plates were noted as loose at 487 miles- once tightened there was no further problems.

It was noted that the tank had very good performance over ‘normal’ terrain, but in mud and slippery terrain, track slip occurred and created a rapid falling off of climbing abilities. It was also said that the tracks were of American design and a superior design with a deeper ‘spud’ could have prevented this slipping. It should be noted that this type of track was featured on the later prototype. Overall, ride quality was described as “very good with no undue pitching or bottoming out”.

It was noted that at 799 miles, the machine weighed, unwashed, 42 tons 8 ½ cwt. It had picked up 2 tons, 2 cwt (224 lbs) of mud, being carried along with the machine. This apparently had very little effect on the vehicle.



Armor layout of the A.33/2. Not shown is the reduction in armor protection along the hull sides of the engine compartment. Also not shown is the tubes that connect the fighting compartment to the escape hatches built into the side skirts. The tubes are made from 1-inch (25mm) thick cast steel. Drawing dimensions and armor thicknesses not to scale. Drawing by R4V3-0N

Excelsior? Commodore?

Official naming changed throughout the life of the project several times, with both ‘A.33 Assault Tank’ and ‘A.33 Heavy Tank’ used interchangeably in documentation. Beyond 1943, it appears to be referred to as an amalgamation of both names, as the ‘A.33 Heavy Assault Tank’. Interestingly, though for a short period of time in November of 1943, documentation and correspondence between the Department of Tank Design and English Electric suddenly begins to refer to it as the “Commodore” alongside Cromwell and Centaur. The name continues for two weeks time and is made mention of several times, before unceremoniously returning to being called the ‘A.33 Heavy’ without any further mention of that name. The name “Excelsior” does not appear in any of the literature related to the A.33. The name may either be a post-war invention or perhaps an internal name, in a similar nature to Vickers’ Valentine. English Electric vehicles may have been titled with an E-name, although proof of this has yet to surface.

Last Gasps

Even from the outset the A.33’s days appeared to have been numbered. The Churchill tanks’ reliability had improved enough to make it unpalatable to introduce another vehicle. Yet further concern was that the vehicle, even if it did enter production, was unlikely to be produced in time for the end of the war in Europe, with it rapidly drawing to a close. It does not appear that the story of the A.33 ended simply with a pair of unsuccessful prototypes, however.

Weekly situation reports from the Department of Tank Design mention that, along with Cavalier (A.24), Centaur(A.27L) and Cromwell(A.27M), there appeared to be a similar effort to mount an improved gun on the A.33. The new gun is stated as being the Vickers-Armstrong designed 75mm HV gun, which was modified with a different projectile to later become the 77mm gun which was mounted on the Comet. English Electric was ordered to contact Leyland Motors for information on work potentially already complete on the remainder of the Cromwell-series of vehicles, and to contact Vickers for the information on the new gun’s mounting. Specifically, it was stated that “English Electric will send a representative to D.T.D. in about 8 days time to go over the general layout of the A.34 turret and mounting installation with a view of incorporating it into the A.33”.

Principally, the plan was to increase the turret ring width to 66 inches in diameter and include a brand new turret design with geared elevation, which was needed given the weight of the new gun. In effect, this meant that the same upgrades that directly created the Comet could also have been applied to the A.33. It’s unclear if the project proceeded past even a conceptual basis, but it was an interesting idea.

Finally, the A.37. Conceptualized as a lengthened A.33 with an additional bogie on each side, additional armor, and a turret housing a 17 Pounder gun, this may have resembled something similar to the A.30 Challenger. Quoted as being 52 tons, and sporting “increased immunity” over the A.33, there is not much known about the A.37 and neither pictures or drawings have yet to surface.

Survivors

One surviving tank, the A.33/2, with the R.L.-type suspension, survives at Bovington Tank Museum. The Vehicle had previously been on display in the museum, first outside, and then inside alongside the A.38 Valiant after receiving its new camouflage paint job. The vehicle has since been taken off public display and is now stored in the Vehicle Conservation Center (VCC) in the Museum’s grounds.



A photograph taken in 1982 when the A.33 was on display outside of The Tank Museum, alongside the A.38 Valiant and an A.22 Churchill. Photo: Richard Crockett.



The A.33 when it was on display inside The Tank Museum.

An article by Trevor Menard

Sources

Department of National Defence(Canada): Subject Files, 1866-1950, Reel(s) C-8286, C-5779

The UK National Archives, WO 291/1439 British Tank Data

The Tank Museum Files (TTM): E2014.364, E2014.526 E2014.528, E2014.531, E2014.533 E2014.354, E2014.535

A.33 specifications Dimensions 7’11” x 22’7 ¾” x 11’ 1 ½”

2.41 x 6.9 x 3.39 m Total weight, battle ready 40 tons Crew 5 (commander, gunner, loader/operator, driver, auxiliary gunner) Propulsion Rolls Royce Meteor, 620 hp at 2550 r.p.m. Suspension “R.L.” Type Bogie Speed (road) 24.8 mph (39.9 km/h) Range ~100 mi (160 km) Armament QF 75mm Mk. V (or 6-Pdr Mk. V), 80 rounds

2x 303 Besa M.G, 5000 rounds in boxed belts

Vickers “K” Gun (twin mount), 2000 rounds in drums Armor 4.5” (114 mm) frontally

No less than 3” (76 mm) combined on all vertical surfaces. Total production 2 For information about abbreviations check the Lexical Index



A33/2 Excelsior, the late version.



An example of what the A.33/A.34 hybrid may have looked like, fitted with the Comet turret and the 77mm gun and the expanded turret ring required for both.

Both Illustrations by Tank Encyclopedia’s own David Bocquelet.