end, over 600 design faults, mainly in the Crossley engine, were overcome. One of the strategies used to minimise problems was to de-rate the engine to 1045 hp (officially quoted as 1000 hp). Rumours persisted that the engine was either war surplus, or formerly from a sub-maritime application. Neither of these are correct, despite some publications suggesting this. The myth may have arisen from Crossley's success in delivering robust engines for marine and other modes of transport. Experience in Western Australia with both Metropolitan Vickers and Crossley engines was otherwise positive. It has been noted that the Irish Railways (CIÉ), through the respected Engineer Oliver Bulleid, had "heard" through the British Admiralty that the "Crossley unit gave no trouble". The Smith Royal Commission into the class identified blind faith in the British manufacturers, and chided the WAGR for ignoring the advice of supervising engineers in the UK who reported problems with the diesel motor during testing. Whilst CIÉ re-engined their similarly powered Crossley 001 Class locomotives to rid themselves of the problem, The Smith Royal Commission recommended against rebuilding, proposing that the entire class be replaced wholesale. To be fair to the WAGR, they were not the only ones that rushed into buying unproven traction: British Railways also did the same, buying many different types of diesel locomotives from many different manufacturers in their haste to dieselise, including purchasing the unsuccessful Class 28 Co-Bo locomotives, which could be regarded as "first cousins" to the WAGR X class. Multiple unit working During construction, 16 locomotives were fitted with multiple unit control and denoted as XA class. These locomotives included communication doors at each end, and were numbered in a separate block starting from 1401. From December 1963, Midland Workshops fitted 10 of the X class for multiple unit working, and these were reclassified as Xb class. Units so converted were not fitted with communication doors, and retained their original 10XX series numbers. Other modifications Whilst the class were built with locomotive pneumatic braking and train vacuum braking systems, during 1969 and 1970 eight of the XA class were modified to operate with dual vacuum/air braking systems manufactured by Davies and Metcalfe to allow them to operate air-braked salt traffic on the Esperance Branch. This equipment was removed in the early 1980s, only to be reinstalled in XA 1406 (October 1986) and XA 1403 (November 1986) to allow these units to haul