Long before diesel traction was common, several mainline services in Devon were being hauled by diesel locomotives and it was the Southern and not the Western that led the way. In the 1940s Oliver Bulleid had designed and built the revolutionary Merchant Navy and West Country Class air-smoothed pacific steam engines. In 1948 his attention turned to diesel power.
Locomotives numbered 10201 and 10202 rolled off the production line at Ashford in Kent in 1951. A third, 10203 was added to the fleet from the Brighton works in April 1954. The engine and transmission were supplied by the English Electric company with a top speed of 110mph.
Bulleid’s influence was obvious – the curved box-like body style closely resembled the carriages the engines would haul. The engines weighed in at 135 tonnes had two eight-wheeled bogies with an articulated inter-bogie connection, each with three axles powered by a separate traction motor per axle and with the fourth non-powered axle in an integral leading pony truck to reduce the axle load.
Locomotive 10202 began a regular diagram early in 1951 running 687 miles each day. Commencing in 29th October the duty covered the 0125 and 1300 departures from Waterloo as far as Exeter Central, and 0730 and 1755 from Exeter Central daily except Sundays. Each day 10202 took on 760 gallons of fuel at Waterloo and was only booked to visit the Nine Elms depot on Sundays for maintenance.
10201 joined her sister in February 1952 and achieved notoriety as the only machine of this type to run beyond Exeter Central-by running away light engine down the 1 in 37 gradient to Exeter St Davids.
In the summer of 1952, the locomotives were re-geared reducing their maximum speed but increasing the load they could haul. Around this time two further diesel locos were added to the London Waterloo to Exeter fleet when numbers 10000 and 10001 were moved from the London Midland Region.
The 1100 Waterloo-Exeter Central (the Atlantic Coast Express), 1630 Exeter Central-Waterloo, 1800 Waterloo-Exeter Central and 2240 Exmouth Junction-Nine Elms freight were now also diesel hauled. On Sundays the engines were used on the 1100 Waterloo-Exeter Central,1656 Exeter Central-Waterloo, 0135 Waterloo-Yeovil Junction and then return 0710 Yeovil Junction-Waterloo.
All five locomotives were transferred to the London Midland Region in April 1955 and steam domination returned to the Southern’s route to Devon and Cornwall for the next 9 years.
All were non-standard with regards to spare parts and servicing and they were withdrawn at the end of 1963.