Friday, March 20, 2015

Matilda-based flail tank II

Patent diagram for the second Matilda Baron prototype showing the drive arrangement, arc of movement of the rotor and rotational direction and diameter of the two sets of flails. Baron I, II, III and IIIA: Mine-clearing versions of the Matilda developed in Britain, 1942-43.

Without getting too bogged down in technical matters, it is important to explain that although two engines were used to power the flail, each with its own starting and cooling system as well as its own clutch and gearbox, the two engines were, in effect, operated as one. The flail gearboxes had been modified to run on first, second and reverse gears only but, from the operator's point of view, this involved just one gear lever, one clutch pedal and one throttle each for the hand and foot. A series of four jointed Cardan shafts from each engine powered the rotor by means of a worm drive at each end of the shaft. Nothing is said, either in the handbook or elsewhere, about any discrepancy of power between the flail drive engines (presumably this was negligible if the two units were tuned precisely), nor what happened if one engine failed.

The rotor itself was the typical Baron type with a central tube of 6in. (15.2cm) diameter surrounded by a framework to which three banks of chains were attached. The ideal flailing rate was around 80rpm, indicated by an engine speed of 1,200rpm. However, by this time two other roles had been envisaged for the Baron. One was wire-cutting, for which purpose a mechanical cross-cutting device, acting more or less on the same principle as hair trimmers, could be activated from the operator's cab. Used in conjunction with rotary side cutters, this operated at first-gear speed, catching and chopping up the barbed wire as it went. There were limitations; too much wire could choke it and if mines were also present, the handbook noted that the tank should only advance into the wire as far as the rotor extended from the front of the tank, about 10ft (3m), then withdraw and flail over the same ground. It was also possible to use the rotor as a crude device for breaking up ground. With the rotor lowered to ground level and rotated slowly until the flail chains were wrapped around it the rotor then proceeded to chew up the ground and wear away obstacles such as anti-tank defences. The driver was supposed to move the vehicle gently to and fro a short distance while this was going on. The process was described by one witness as 'somewhat akin to the scratching of a dog'.

The failure of the first hydraulic system, run from the tank's original turret traverse gear, encouraged Rackham and his team to develop something stronger, with a separate hydraulic pump driven off each flail engine. Operating via a common reserve oil tank and a control unit in the operator's compartment, the pumps were used to activate big hydraulic jacks that raised and lowered the rotor booms as required. Some reasons for raising and lowering the rotor have already been described. Another would be in order that the tank could drive in the normal way without the flail chains touching the ground and it would also cut down storage space if the Barons could be parked with the boom from one overhanging the engine deck of the vehicle in front.

Illustrations in the handbook suggest that a good deal of the hydraulic plumbing around the control cab was woefully exposed to potential damage when the vehicle was clearing mines or under fire, but these may show a pre-production machine. It does, however, seem clear that on the Baron IIIA the operator was expected to exploit the easy movement of the booms by following contours in the ground so that deep hollows might not be missed and bumps not struck by the rotor. Operators were informed that a height of about 4ft 6in. (1.4m) was best for the rotor (given that the flail chains were not damaged) in order that each chain would strike the ground at around 60mph (96.5km/h), which was sufficient to detonate a German anti-tank mine buried up to 4in. (10.2cm) in the ground.

The greatest drawback to the Baron was, with an engine at each side, its overall width of 13ft (4m). This prevented it from crossing a normal Bailey Bridge or from passing through the bow section of a contemporary landing craft, both serious operational limitations. In addition, as the handbook explains, it was a logistics nightmare since for transportation, presumably by rail, both flail engines had to be removed, as did the rotor, rotor arms (in four pieces), along with the Cardan shafts and gears.

One experiment, which theoretically would have applied to all flails, was the idea of rotating the chain drum in the opposite direction, that is to say anti-clockwise if one were watching the tank from the right. Trials suggested that reverse flailing gave a higher percentage of detonations but, since these now happened a lot closer to the tank than with conventional rotation, the practice was abandoned. It is also worth remarking that with the flail going round in the regular way there were instances of live mines being thrown up by the chains and landing on top of the tank. Generally this was not a problem even if the mine detonated, so long as the crew were totally closed down.

Production of the Baron IIIA was placed in the hands of Curran Brothers of Cardiff in 1942. They were given an initial contract for 60 conversion kits with a promise of 60 more to follow. The idea was that the kits would be delivered to Matilda battalions earmarked for conversion. These would then be visited by travelling teams of trained fitters working in conjunction with local REME workshops. Space had been arranged to ship a dozen Baron IIIAs to the Middle East, but they could not be completed in time and, as far as is known, none ever went abroad. Some were issued to No.1 Assault Squadron Royal Armoured Corps (RAC) which, on 29 July 1943, was placed under command of General Hobart's 79th Armoured Division where it was ultimately absorbed into 43rd Royal Tank Regiment, which became the division's experimental trials unit.

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