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A21 Infantry Support Tank - A British StuG Story

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apophenia:
This sprang out of a simple notion for an early-WW2 British StuG analogue. But do any of my backstories stay terse? Nooo ...

So, with the promise of a captive audience incarcerated by 'social distancing', I have given free reign to my natural verbosity  >:D
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Alaric Tank: Born of the Franco-British Bilateral Defence Coordination Committee

Both Britain and French were naturally threatened by the German remilitarization of the Rhineland in early March 1936. Hilter claimed this move to be, in part, a response to the Franco-Soviet Treaty of Mutual Assistance signed a week earlier. After German troops moved into the Rhineland, the Popular Front government in France sought out reassurances from their British ally.

Léon Blum's 1936 Popular Front government assigned the role of maintaining the military alliance with Great Britain to Minister of State (and former PM) Camille Chautemps. [1] To that end, a commission was established in early 1937 aimed at encouraging defence production coordination between the two nations. This working commission would become the Comité de coordination de la défense bilatérale franco-britannique or FB-CCDB.

'Every Time!': Asking for Assured Assistance While Manouevring for Advantage

Chautemps' British opposite (appointed in May 1937) was the Permanent Under-Secretary of State for Foreign Affairs, Sir Robert Vansittart. [2] Both men would spend much of their time managing the natural competitiveness of representative of their militaries and the excessive industrial proprietariness. The recent nationalization of much of French strategic industrial firms also served to unsettle British company representatives. Nevertheless, the need for cooperation was apparent to both sides and some progress was made.

The British Army was most intrigued by the performance of the '7.5 French' cartridge which had been introduced in 1929. [3] Also of interested was the Hispano-Suiza HS 404 20 mm auto-cannon. British authorities also suggested joint development of a medium artillery piece - as replacements for British 127 mm BL 60-pounders and the various aging French 105 mm howitzers and guns. In this, the British were supremely confident in the capabilities of their pending BL 4.5 inch medium field gun. This 114 mm gun, it was argued, would have superior range to the German 10.5 and 15 cm pieces.

For their part, the French were interested in the performance of the British Army's recently-adopted Ordnance QF 2-pounder anti-tank gun (although less so in its complex carriage). Samples of another Vickers design, the QF 3.7-inch AA gun, were also requested. This was primarily for comparisons between the characteristics - both shells and pieces - of Vickers'  gun and the proposed adaptation of 90 mm naval guns from Établissements Schneider for the DCA (Défense contre les aéronefs) regiments. [4] The ultimate goal was a common heavy AA calibre - either the French 90 mm or British '94 mm' depending upon the outcome of comparative trials.

'Every Time!': Asking for Assured Assistance While Manouevring for Advantage

Most of the posturing at FB-CCDB meetings amounted to little more than thinly-disguised industrial espionage. The concept of adopting common munitions calibres was a good one but neither side was willing to simply accept earlier decisions by their ally. In the end, the French stuck with lower-performing 47 mm tank/anti-tank guns and 105 mm field guns. And the British went it alone with their 94 mm anti-aircraft guns and 114 mm medium field guns.

The armoured forces of each nation had little interest in their opposites - both sides believing their own approach to be correct ones. However, representatives of the Royal Armoured Corps were interested in French technical developments. To that end, samples of the new Somua S35 and the Char B tank were requested for review. It was quickly concluded that the forthcoming Matilda II would be the equal or superior of the S35. However, the potential of the older Char B as an infantry support vehicle was appreciated. It was decided - primarily in the interest of maintaining relations between allies - that the RAC would field an 'anglicized' version of the Char B bis.

(To be continued ...)
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[1] Chautemps was a member of the centre-left Parti radical while Léon Blum headed the socialist party SFIO.

[2] Vansittart had also been  Principal Private Secretary to PM Baldwin. However, Sir Robert strongly disagreed with disarmament plans of both Baldwin and the in-coming Premier, Neville Chamberlain. It has been suggested that the latter used an appointment to the FB-CCDB to sideline Vansittart.

[3] Of particular interest was the 'heavy ball' Balle 1929D with its boat-tailed spitzer bullet for the drum-magazined Mle 1931F machine gun.

[4] The French were acknowledging the inherent limitations of their Canon anti-aérien de 75mm modèles 1932 and 1938 guns. In the end, the DCA would take on the Schneider guns as their canon de 90 mm modèle 39S.

apophenia:
Late 1930s British Tank Developments - From 'Shelled Area' to 'Infantry Support'

With war-clouds looming, the British Army's Mechanisation Board began the concept design for a new infantry support tank capable of dealing with WWI-like trench warfare conditions. This design would emerge as the A20 Shelled Area Infantry Tank, prototypes of which would be built in Belfast by Harland and Wolff. However, the General Staff favoured the interim introduction of an 'anglicized' Char B to fill in until delivery of the A20. Accordingly, Dr. H.E. Merritt, Director of Tank Design at the Royal Arsenal, Woolwich, was detailed to the Mechanisation Board to oversee the modification of the Char B design for British service.

From the outset, it had been decided to import Char B track system and advanced hydraulic suspension units directly from France. This was partially in the spirit of the FB-CCDB but also a practical consideration considering the small numbers involved in an interim purchase. Whitehall also insisted that the armoured body itself be entirely constructed in the UK from British plate. Since Harland and Wolff were engaged with the A20, work on the British Char B - now designated A21 - was assigned to W.G. Allen & Sons, boiler-makers at Tipton in Staffordshire, but with armour experience dating from WWI.

Reports from trials with the loaned Char B1s were rather critical. Some issues were moot. The AMX1 one-man turret was judged exceedingly impractical. However, since the General Staff required a rooftop unditching beam, British vehicles would be turretless in any case. The Renault 6-cylinder petrol engine was reliable enough but Whitehall had already dictated that a British-made engine be used. Most troublesome was the Chaize Naeder hydrostatic system - essential in the Char B for traverse in azimuth (since the gun itself had only 1 degree of traverse for 'fine-tuning'). Fortunately, the General Staff had requested that the main gun be raised to increase ground clearance and allow for manual traverse on the 'anglicized' Char B.

The dictate of a British-made engine was further complicated when the General Staff expressed preference for a diesel engine. Dr. Merritt judged a diesel impractical within the time constraints (no powerful-enough British diesel then existing which was suitable for tank use). Instead, the British Char B would be powered by the Bedford Twin-Six - a new horizontally-opposed petrol engine developing 325 hp at 2,200 rpm. Transmission would be a a Meadows 4-speed and reverse crash gearbox with control via a Merritt-Brown system - also built by David Brown Ltd. but designed by Henry Edward Merritt himself.

The resulting design was initially dubbed A21 Accordance but this nomenclature was amended to A21 Tank, Infantry Support, Mk I, Alaric IA before the first prototype was rolled out in the early Summer of 1938. The Alaric IA was armed with an Elswick QF 12-pounder 12 cwt gun - a 3-inch former naval piece. Although close in calibre to the Char B's French gun (76.2 mm versus 75 mm), the 12 cwt gun had a much longer barrel - 40 calibres (ten feet) versus the Char B1 gun's stumpy 17.1 calibres. In service, this reasonably high-velocity gun was given the short-form of '3-inch-40'. Fortunately, the Bedford Twin-Six proved shorter than the Renault engine which allowed the fighting compartment to be slightly lengthened. With the large '3-inch-40' mounted, every inch counted.

Top An Alaric IA of the Dorset coastal defence force in late June 1940. A3802 'Alexander' was a crew trainer based at the Armoured Fighting Vehicles School, Bovington, but has been 'gunned up' and deployed south to West Bexington on the Dorset coast.

Note the portside hull door and more upright driver's hood unique to the Alaric IA. Distinct features of this particular vehicle are the muzzle brake fitted to the main gun (presumably a piece which had been under test at the Lulworth Gunnery School prior to being fitted) and a commander's turret taken from an obsolete light tank.

Developments and Evolution of the A21 Infantry Support Tank

Changes in British Infantry Support Tank policy were dictated by slow progress on the A20 and urged on by the 'Sudeten crisis' of the summer of 1938. This prompted an order for increased production of the 'interim' A21 Alaric. [1] Since supplies of '3-inch-40' guns were limited, [2] a new main armament would be needed. This resulted in a proliferation of proposed new sub-types of the A21 Tank, Infantry Support. The Alaric IB was to have a heavier 12-pounder gun but never reached the hardware stage. [3] The Alaric II was armed with a QF 13-pounder 9 cwt - an anti-aircraft gun pulled back out of retirement. The Mk II made it to the prototype stage (based on an incomplete Alaric IA hull) but it was decided to deploy available QF 13-pounder 9 cwt guns as reserve AA artillery instead. A related project, the Alaric IIA was to use a hybrid 3-inch gun-howitzer but this 'tube' never appeared. [4]

The follow-on development which did reach production was the so-called 'Expeditionary Alaric'. The production model Alaric IV was armed with a 'French 75' gun. The latter were chosen specifically for commonality with the French allies but the guns themselves were sourced from the United States. As affairs 'heated up' in Europe, the Americans made clear through 'back channels' that their military was willing to part with some of its older equipment. This included stocks of 75 mm field guns - both French-made M1897A2 and US-made M1897A4 models. All of these ex-USA guns had non-updated and rather worn carriages but that was not a concern for use in Infantry Support Tanks. Accordingly, the American guns were lightly refurnished and adapted for vehicle use.

A major advantage of the '75' was its fixed ammunition. The British 12-pounder guns all had separate casings and projectiles requiring a 'holder' to keep them together for loading. The move to the '75' greatly simplified the job of the Alaric's loader. But overall, Alaric IV gun performance reduced compared with the Alaric IA. The L/40 '3-inch-40' had a muzzle velocity of 2,210 ft/s and a rate of fire of 15-20 rounds per minute. By comparison the L/36 75 mm had a muzzle velocity of only 1,600 ft/s but, with its 'fixed' ammunition had a potentially higher rate of fire. HE shell weight was similar - 12.9 lbs for the '3-inch-40' and 12 lbs exactly for the 'French gun'. So, the '75' was a compromise but one softened by its availability in fairly large numbers.

Bottom 'Expeditionary Alaric' - a 75 mm '3-inch-40'-armed Alaric IV of the 4th Royal Tank Regiment, British Expeditiary Force. One of 18 Alaric IIs deployed to France in May 1940, A3844 'Alcuin' was knocked out in a divebomber attack outside of Mercatel during the Battle of Arras. (The crew abandoned their vehicle after setting it alight and joined the retreat on foot before being captured south of Duisans.)

In evidence are the more sloped driver's hood of the Alaric IV (and IIA). This is a standard vehicle but 'Alcuin' has had a French-style camouflage stripe added as well as unofficial, WWI-style 'tactical' markings near her nose. A small RAC pennant flies from a wireless antenna.

Importing US surplus stocks of 75 mm ammunition continued until the outbreak of war. However, production of 75 mm ammunition was already underway in Britain prior to September 1939. One indirect result of that was the development of the 'domestic' Alaric V with its '3-inch-36' gun. The latter was another hybrid born of necessity. The best of the ex-US '75s' had been installed in Alaric IIAs. However, many of the older M1897A2 and M1897A4 tubes were found to be quite worn. [5] Rather than boring out and lining already elderly weapons, it was concluded that minimal work would be required to get the '75' to chamber and fire the slightly larger British 3-inch projectile. Accordingly, the British-made 75 mm casing was adjusted to accept the fractionally larger 3-inch shell. [6] Initially, the Alaric V was to be a limited production training model. As events unfolded, the Alaric V trainer with its '3-inch-36' gun would become an essential component of Home Defence after Dunkirk.

(To be continued ...)
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[1] BTW: There was a RW A21 project. It was to have been a developed A20E2 Shelled Area Infantry Tank but Harland and Wolff's A21 was passed over in favour of the A22 Churchill.

[2] The QF 12-pounder 12 cwt guns were also in demand for shore defence installations.

[3] The QF 12-pounder 18 cwt was another ex-naval gun which, in the end. While a potentially hard-hitting gun, a separate shell and cartridge made it extremely impractical for tank use.

[4] The proposed 3-inch gun was based on the pending Ordnance QF 25-pounder piece. The modifications consisted of breech and barrel liners reducing the bore down from 88 mm to 76.2 mm (essentially the same mods use to create the Mk II's QF 13-pounder 9 cwt during WWI).

[5] Indeed, this wear would have been one of the reasons why such guns had not been selected for the US Army upgrade prorammes.

[6] There was only .0472 of an inch difference between 'French' and British projectiles. This could be accommodated by a slight enlargement of the cartridge's copper driving band. In metric measures, the French (and American) 75×350 mm R round became a 76.2x350 mm R for the '3-inch-36' gun.

GTX_Admin:
Interesting

tankmodeler:
Very cool. One might imagine that if the A21 served in combat for more than a few months (as the French Char Bs only did) the Brits might have seen their way clear to deal with the CharB's second largest flaw after the 1-man turret, the huge radiator weak points on the hull sides. Offset armoured covers over the grilles permitting air ingress, but not shells would seem an obvious improvement on the design. As would some sort of commander's cupola permitting better lateral (at least) visibility for the commander, if not the driver. A slightly raised superstructure area to permit the fitting of a radio in each tank and the cylindrical cupola from a Matilda II, mught be a good Mk V design?

apophenia:
Cheers folks.

tankmodeler: Agreed that the AMX turrets were dreadful. The AMX4 was meant to be an improvement - it was enlarged just enough for a second crewman to squeeze his shoulders inside the turret in an emergency. Était-ce ergonomique?  :P

On the radiators, I've read conflicting reports. Some sources say that they were successfully targeted by German 3.7 cm Pak 36s. Others claim that the louvres offered protection equivalent to 60 mm of armour plate. But which version is correct?

With the RW Char B, there was sufficient room inside to have a corridor running along the starboard side of the engine. Presumably, any crew member attending to that engine would have to crouch. Why they didn't lower the ceiling a smidge and mount those two radiators on the roof is anyone's guess.

Another curiosity is the appareil Naeder at the stern which was almost as long the Renault engine. So, first chance I got, that hydrostatic system got junked. My British HO12 engine would need to be mounted fairly high up to meet its new transmission. I had a vague notion that this boxer engine could sit above a fuel tank ... not sure if that's ever been done or even if it would be practical.  ???

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