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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