The WAGR X class group comprised 48 diesel electric locomotives built for Western Australian Government Railways by Beyer Peacock and Metropolitan Vickers, at Bowesfield Works, Stockton-on-Tees between 1954 and 1956. They were fitted with a Crossley HST-V8 engine. At the time of construction, this engine was untested for rail traction, though the engine itself was an evolution of a design used successfully in patrol boats during World War Two. 
The engines used exhaust pulse pressure charging and was rated at 1,200 horsepower (895 kW) at 625 rpm. There were no valves, and inlet and exhaust were via ports in the cylinder walls.
The same engine, and some of its derivatives, were used in CIE locomotives (e.g. CIE 001 Class), and the British Rail Co-Bo (BR Class 28). Crossley Brothers, like many others at the time of the Modernisation Plan on BR, were hoping to expand into railway traction. Their foray was an unmitigated disaster. Failures commenced within weeks of the first locomotives being unveiled. It was only the skill of staff at Midland that saved the day. The Smith Royal Commission into the class identified blind faith in the British, and chided the WAGR for ignoring the advice of supervising engineers in the UK, who reported problems with the traction motor during testing.
In their early days, availability was less than for steam. Whilst the Irish re-motored their Crossley locomotives to rid themselves of the problem, The Smith Royal Commission recommended against this, and proposed the purchase of further locomotives of "proven design" to remove the class completely. The motors burnt oil, had underfed bearings, vibrated and popped heads and pistons. It was only the engineering excellence, and perseverance of Midland Workshops staff that kept the locomotives operating, and performance improving. In the end, over 600 design faults, mainly in the Crossley Engine, were overcome.
For these reasons, it would appear the engine was derated to 1105 flywheel bhp, yielding a net of 1045hp for traction. The sources differ on this point, which may reflect the various rack settings used over their extended lives. From memory, the WAGR leaflet on the class cited 1000hp for traction.
The main generator was a MetroVick MV TG4203 delivering current to four MV136 traction motors. These were fitted to the four axles mounted directly to the frame. Two idler trucks each with two axles were mounted at each end, giving a total of 8 axles, 4 of which were motored. The unit was of cowl construction with a bullnose type cab at each end. They weighed 79 ton (80t) and had a maximum speed of 89km/h.
The first group of 32 were all originally classified X and numbered X1000-1032. A second group of 16 was ordered, with the addition of multiple unit (MU) controls. These were fitted with a gangway through the bullnose of each cab, classified XA and numbered XA1401-1416.  MU operation was successful. As a result, 10 of the original X class were modified for MU and reclassified XB. They were not renumbered.
In their final years, those still in service were reputed to have performed well. They ran grain trains in the South West as late as 1984, and provided power for trains following the reopening of the Fremantle line. During the period of suburban electrification works, X class locomotives hauled 5-car trains made up of QR SX stock. The locomotives concerned were fitted with air brakes for that role. (If known, please advise Admin which X class were fitted.)
The last of the class in service was XA1402, stored 31 March 1988. Six in total over the three subclasses have been preserved. The locos carried names of Indigenous groups and individuals. 
Sources include: Wikipedia, Locopage database, WAGR leaflet, forums and newsgroups
1.^ Doncaster, N: The Crossley Experience "The Partyline" - the in-house magazine of Steamtown Peterborough. Number 71, Spring 1998
2.^ a b Obern, L Locomotives of Australia, Reed Books 1975
3.^ Smith Royal Commission (dates pending)
4.^ Renehan,D: "Crossley diesels of CIE". Journal of the Irish Railway Record Society, Vol. 15 pp25-35 and 70-79
5.^ Richardson, L.C. The Western Australian Government Railways X-Class Diesel-Electric Locomotive Australian Railway Historical Society Bulletin, March 1955, pp25-28
6.^ "XA Diesel Loco". Hotham Valley Railway website. Hotham Valley Railway. Retrieved 19 September 2012.
7.^ "Tindale's Catalogue of Australian Aboriginal Tribes". South Australian Museum website. South Australian Museum. Retrieved 18 September 2012.
We identify rebuilt and renumbered locomotives from this class as well as other classes with similar mechanical configurations and present those classes below.
|Manufactured by||Metropolitan-Vickers, Stockton-on-Tees, UK|
|Number in database||16|
|Weight||78 ton (79t)|
|Tractive effort||116kN start, 53kN cont @ 39km/h|
|Axle load||Nominally 10 ton for 45lb lines|
|Number in database||16|
|Preserved - Operational||4||XA1401 XA1402 XA1405 XA1411|
|Preserved - Static||1||XA1415|
|Scrapped||11||XA1403 XA1404 XA1406 XA1407 XA1408 XA1409 XA1410 XA1412 XA1413 XA1414 XA1416|
|Road number||Gauge||Status||Last owner||Last operator / caretaker|
|XA1401||Narrow1067mm||Preserved - Operational||Hotham Valley Tourist Railway||Hotham Valley Tourist Railway|
|XA1402||Narrow1067mm||Preserved - Operational||Rail Heritage WA||Rail Heritage WA|
|XA1405||Narrow1067mm||Preserved - Operational||Rail Heritage WA||Rail Heritage WA|
|XA1411||Narrow1067mm||Preserved - Operational||Hotham Valley Tourist Railway||Hotham Valley Tourist Railway|
|XA1415||Narrow1067mm||Preserved - Static||Privately owned||Hotham Valley Tourist Railway|
Please note - in the case of scrapped, renumbered or rebuilt locomotives, the last operator or owner is listed.