Locomotive 21C139 was built in 1946 at the Southern Railways works in Brighton and entered traffic on 16th September in full Southern malachite green livery.
 It was based at Stewarts Lane shed working trains principally from London Victoria station to the Kent coast resorts of Margate and Ramsgate and the ports of Folkestone and Dover.
21C139 received the name 'Boscastle' (after the attractive North Cornish village) some time between 1947and1948.
After nationalisation in 1948 'Boscastle' received the number 34039 and betweenJuly and September became the regular engine on the prestigious 'Golden Arrow' pullman train.

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Courtesy E.Wilmshurst

In November 1948 'Boscastle moved to Brighton shed, working to such places as Salisbury, Bournemouth and Southampton. Other duties included late night trains parcels trains from Brighton to London, returning on the early newspaper train from London Bridge.
'Boscastle' became the first West Country to carry the new standard British Railways passenger green livery in August 1949.

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Courtesy J.G.Tawse collection

In 1951 Brightons allocation of West Countrys were dispersed elsewhere and 'Boscastle' was chosen, along with two others for trials on the Eastern Region in May.

Based at Stratford shed (London) they worked services from Liverpool Street to Cambridge, Norwich and Harwich. During this time 'Boscastle' visited Bury St Edmunds ( where it was too long for the 50' turntable) and Doncaster, presumably on a special working.

The trial was not a great success due to the crews unfamiliarality with this type of locomotive and the problems of getting fitters and spare parts across London when they required attention, which they frequently did.

'Boscastle' returned to Brighton in March 1952 and settled down to a relatively quiet life. The schedules of the cross-country trains were not particularly demanding and Brightons 'West Countrys' were only really tested by summer Saturday trainloads.
In November 1958 'Boscastle' was due for a Heavy General overhaul and was sent to Eastleigh works for rebuilding at the same time.