4920, built in 1939 to diagram 3192 and order number 1043, was the first of the three sorting vehicles built to this order. Initially allocated to the Western Section of the Southern Railway it would have worked the 22:30 Waterloo to Dorchester via Southampton Terminus and the 21:55 Dorchester to Waterloo via Southampton Terminus. However by June 1958, 4920 was acting as a spare to 4921 and 4922 on the same route. By September 1961 the vehicle was back in service with two ex GWR vehicles being used as spares. Soon afterwards 4920 was transferred to the Eastern Section to work the London to Dover service. 4920 was then withdrawn from service in early 1977 while carrying the standard BR Blue and Grey livery.
Known pictures of 4920 in service include:
6th July 1961 at Dorchester in BR Southern Region green, numbered S4920S - picture by H.C.Casserley 
Undated photo in BR Southern Region green, numbered S4920S - picture by B.J.Harding 
5th June 1975 at Ashford in BR blue & grey as S4920 - Unknown photographer 
 published in 'Maunsell's SR Steam Passenger Stock 1923 - 1939' by David Gould
 published in an article in Back Track
4920 was claimed by the National Railway Museum at York for preservation upon its withdrawal and placed on loan to the Nene Valley Railway, arriving at Wansford in either 1978 or 1979.
Since then it has been used as a museum at Wansford giving visitors a chance to experience a TPO and have their own go at sorting the mail.