Experiments with two double locomotives to France and Roumania during the late 1930's powered by Sulzer 'double-bank' engines had been successful, the four machines were still operating as Derby set to work on the BR/Sulzer Type 4's.
These early machines were too large for Britain's loading gauge, their LDA31's were pared down to LDA28's, more useful for fitting into locomotives destined for restricted European loading gauges.
However in May the class was scattered up the WCML for crew training, D1 to Longsight (9A); D2 & D9 to Edge Hill (8A); D3, D8 & D10 to Crewe (5A); D5&6 to Carlisle (12B) - something of an odd move in light of the English Electric Type 4's being the predominant diesel on the WCML expresses and that the more powerful Peaks soon to come out of Derby & Crewe would end up almost everywhere but the WCML. They would also be frequently found on the Euston - Blackpool & Crewe - Perth workings.
Reallocations at this time centred on returning the locomotives to Camden (1B), but they would continue to be active intermittently on the St Pancras - Manchester services. One particular working associated with the Class on the WCML was the 7.45am Crewe - Euston.
The Modernisation Plan which called for the replacement of steam by diesel and electric traction presented the architects of the Plan with many questions, often with a multitude of answers.
In many cases there was no definitive 'right' or 'wrong' answer, the global use of diesel locomotives was still very much on a learning curve, with some solid successes and also many dead ends.
Nevertheless these were still large engines particularly when coupled to the large generators required to convert that mechanical energy into electricity.
These heavy internal components required substantial framing and support from the body, which was also filled with auxiliary equipment, train heating boilers, water and fuel, all red flags for those trying to keep the axle loadings as low as possible.