supplied with power from the current rails, and at half that speed when working on batteries. The metadyne-fitted locomotives had new bodies, but the bogies and motors were removed from redundant Metropolitan line stock and refurbished at Acton Works. Similarly, the metadyne equipment was removed from an experimental train and reused. A metadyne unit consists of a rotating machine, which converts the constant voltage supplied by the battery to a constant current, which feeds the motor. The metadyne system is more efficient than conventional starting resistances, particularly when the locomotive starts and stops frequently, or when it needs to run for long periods at slow speeds. For cable laying work, the metadyne-equipped locomotives could pull trains of 100 tons at for considerable distances, without any sign of overheating. Despite the advantages, their complexity resulted in them becoming unreliable, and they were withdrawn in 1977. L41 and L42 were scrapped soon afterwards, but L43 was used for testing purposes for a further three years. The locomotives fitted with GEC controls used an electro-pneumatic controller, with 28 steps, which allowed the four motors to be connected in series, in two parallel-series pairs, and all in parallel as the speed increased. Pairs of locomotives could be operated in multiple, and motors 1 and 3 or 2 and 4 could be selected if there was a failure of the other pair. As built, the vehicles were long, and could pick up power either from a standard four-rail configuration, or the three-rail configuration of the Central London Railway, until it was converted to four rails in 1940. The next batch of seven vehicles were manufactured by R. Y. Pickering and Co Ltd, who were based in Wishaw, Scotland. The traction control equipment was by GEC, although the batteries had a larger capacity than the previous batch. The motors were reused from passenger stock which was being withdrawn at the time. One important improvement was the addition of runners and a lifting device, which enabled any battery cell to be removed from its rack and lowered to the ground through an aperture in the floor. This feature meant that the batteries could be changed without using an overhead crane in a lifting shop, freeing it for more important work. An eighth locomotive was built by staff at Acton Works in 1962, partly as an exercise to prove that the workshop could compete for this type of