In March 1947, the LMS announced its intention to operate main line passenger services using diesel traction: initial specifications were for a pair of 1,600 hp locomotives with a top speed of 100 mph, capable of hauling express services such as the Royal Scot.

[citation needed] The company also announced it intended to use the same type singly on semi-fast suburban and medium weight freight services such as were hauled by 2-6-4T engines; English Electric engines were specified of similar design to that used on the company's diesel electric shunting locomotives.

[7][8] The bogies took an American pattern design, which was modified by Edward Fox and his team at Derby to create a smooth riding suspension.

[clarification needed] The welded bogie frame was derived from Fox's earlier design for Liverpool-Southport electric trains.

[9] The primary suspension consisted of equalising beams with coil springs;[4] the equalising beams were located within the bogie 'sandwich type' side frame,[10][11] whilst the secondary suspension utilised a two bolsters per bogie incorporating four transverse leaf springs.

[4][12] The locomotive weight was carried on four sliding elements on the bolster, with a centre pivot used to transfer tractive forces.

[7] The locomotive body was a cowl unit design, consisting of structural longitudinal members, with cross stretchers forming the supports for the internal equipment including the engine-generator.

The locomotive superstructure was mechanically separated from the load-bearing structures by pivots at either end of the body and incorporated roof doors for access to the diesel engine.

English Electric supplied the engine from its Rugby factory, the DC Generator from its Bradford works, and Traction Motors from Dick, Kerr & Co. in Preston.

[citation needed][ii] Vacuum brakes were from Westinghouse, and the oil-fired train-heat boiler was from Clarkson.

[17] Each axle was powered: the traction motors were axle-hung, nose-suspended, driving the wheelsets via a single reduction gear.

10000 underwent tests on the line between St Pancras and Manchester, the schedule being set to timings based on a standard 4-6-0 (5X) passenger express locomotive.

10000 was placed on a twice-daily London-Derby (128.5 mile) return passenger service, hauling trains of 300 to 450 gross tons.

At the gradients leading to Shap and Beattock, the engines operated at full power, hauling the trains at 38 and 36 mph in each case.

After June 1949, the units operated for over two months in multiple formation - working London-Carlisle and later London-Glasgow services.

One notable freight working was the haulage of a 60 wagon, 1,100 ton gross coal train, between Rugby and Willesden, achieving 25 mph on a 1 in 133 gradient to Tring Summit.

Due to boiler problems sometimes leaving them unable to provide carriage heating, they often worked freights in winter and the Royal Scot in summer.

[clarification needed] Both locos were subject to preservation attempts from railwaymen who appreciated the change and improvements gained by the switch to diesels.

[citation needed] In 2011, the Ivatt Diesel Re-creation Society announced plans to build a replica of no.