The bolsterless bogie design was similar to that used on the Bulleid/Raworth electric locomotives, CC1 and 2, introduced in 1941, with similar bearing pads, wheels and the mounting of the bogies and brakes. To carry the additional weight an articulated pony truck was included, ingeniously guided by links fitted to the bogie front plate which also carried the buffers, this also had the effect of improved riding and reduced track wear. Six nose-suspended, axle hung traction motors were fitted driving three axles on each bogie. The profile of the body sides was curved to match the profile of the Bulleid coaches of the time. Steel panels riveted to rolled steel section framing was used throughout, apart from the hinged engine covers which were made from an aluminium alloy.

The driving compartments included a main controller, driver's brake valve, control switches and indicator lights and alarms connected with the automatic control system. The 'deadmans' facility was located in the desk opposite the driver's seat and had two treads to suit either seated or standing driving positions. The engines were fitted for left hand drive. The enginemen were looked after with two seats, an electric cooker, handwash basin and a lavatory.

An automatically controlled oil fired boiler provided carriage steam heating. Water filling access was via a small hatch located on the bodyside at the number two end.

In February 1953 Brighton Works commenced assembly of the third member of the fleet, N°10203, which was completed in March 1954. A number of technical differences were incorporated in this loco, the most significant being the installation of a higher powered engine developing some 2,000hp. After its commissioning trials, N°10203 based at Nine Elms joined 10201/2 on the Waterloo-Exeter line where it demonstrated its superior output. N°10203 was fitted with a Mk II engine developing 2,000 bhp at 850 rpm whereas 10000/1 and 10201/2 were fitted with Mk I versions of 750 rpm rated at 1600 and 1750bhp respectively.

Using steam locomotive designations, the power classifications were 6P/5F for 10000/1 and 10201/1 and 7P/6F for 10203.

N°10201 was completed in November 1950 and commenced tests, including some trials on the London Midland region between St Pancras and Derby. N°10201 was then displayed at the South Bank, Festival of Britain Exhibition from May 1951 and was not returned to normal traffic until the September of that year. From then both engines worked alternately with a Bournemouth line diagram.

In early 1952 both the locos were overhauled at Brighton Works, returning to the West of England line within a short period. In April 1952 a series of controlled road tests were carried out on the Waterloo-Salisbury route using N°10202 hauling 11 bogies plus a dynamometer car. In November 1952 both were again taken out of service and sent to Brighton Works for a number of modifications to be carried out, including re-gearing to increase tractive effort. By Spring 1953 both were returned to the Western section and continued main line operations.

N°10201 was unintentionally the only one of the Bulleid diesel engines to run beyond Exeter Central by running away light engine down the 1 in 37 gradient to Exeter St Davids! Despite weighing in at 135 tons, N°10201 and N°10202 were given a wide route availability and were actually passed to run to Plymouth through Okehampton, but none ever did so.

Bulleid's N°10201 and N°10202 were joined in March 1953 by N°10000 and N°10001, initially on Bournemouth line turns but from the Summer timetable four interworked diesel diagrams were created. Until their appearance on the Southern 10000/1 had spent most of their time on fitted freights due to being equipped with small and unreliable train heating boilers - although for the summer of 1951 a daily 703 mile duty between Euston and Liverpool was regularly worked when train heating was not required. New boilers were fitted to N°10000 and N°10001 for SR duties and along with the re-geared N°10201 and N°10202, four regular diagrams worked in Summer 1952 (with acknowledgement to the Southern Electric Group's website for this information).

For a period during 1954, N°10202 was used on all four daily workings of the "Golden Arrow" and "Night Ferry" a "Golden Arrow" headboard with the two words separated by a diagonal arrow was the only embellishment carried by the engine.

In April 1955 N°10201 and N°10202 were reallocated to the LMR at Camden for use alongside N°10000 andNº10001. N°10203 continued to operate on the SR until July 1955 when it too was reallocated to the LMR.

N°10201 and N°10202 generally worked double heading services such as the "Royal Scot", whileNº10203 was deployed on Euston-Bletchley workings, but did however on occasions make trips to Manchester, Carlisle and Glasgow.

Whilst on the LMR the chime whistle was also replaced by twin air horns.

By the end of the 1950s the locos saw less and less work, being used on secondary passenger and freight duties. In November 1962 N°10201 and N°10203 were taken out of service and stored at Derby, being joined by N°10202 in early 1963. At the end of 1963 all three were withdrawn and unfortunately sent for scrap.

When built all three were painted in black livery with silver lining, including silver frames, whilst the centre of the roof section was matt black. After the locos were allocated to the LMR, Derby Works outshopped all three in BR standard locomotive green and replaced the waist height silver band with orange and black lining. The roof however was painted a really practical primrose yellow! This of course soon ended up a dirty black colour. Near the end of their working lives they sported small yellow warning panels at each end.