[3] The Class 15 was ordered by British Railways (BR) shortly after the announcement of the 1955 Modernisation Plan, which led to the procurement of a diverse number of diesel locomotives under the 'pilot scheme'.

There was also a strong political desire to support British manufacturers in transitioning towards the design and production of these favoured forms of traction.

Due to a lack of expertise, this often involved the pairing of traditional locomotive manufacturers with various firms within the electrical sector, even though the latter typically had very limited experience of the railways.

[4] In accordance with these policies, BR ramped up its efforts to convert its fleet, placing numerous orders within a short timeframe for diesel locomotives to several different specifications with various manufactures.

The first batch of locomotives was primarily intended for evaluation purposes, this initiative coming under the remit of BR's pilot scheme.

[4] While BTH was appointed as the main contractor and was viewed as being capable of designing the type, the company lacked capacity at its facility in Rugby, Warwickshire, and thus was unable to produce the locomotives inhouse.

[4] The propulsion system consisted of a single Paxman 16YHXL engine that provided up to 800 hp (597 kW) that, via a diesel-electric transmission, drove four individual DC traction motors.

An example of such an occurrence was on the northbound Fenman on 6 January 1961 where D8236 hauled the train, including the failed Class 31 D5665, from near Stanstead to Bishop's Stortford where a more powerful replacement took over.

[4] A series of modifications to the pistons, piston rings and maintenance schedules, and fitting cast iron cylinder heads led to considerable improvements in the engine's reliability, however, it remained a complex V16 for only providing 800 bhp, while the small size of the class bore poorly at a time when the rail network was rapidly contracting.

[4] Additional factors highlighted by Bradley include a general dependence upon the wider British electrical industry to both design and deliver numerous subsystems that would function sufficiently well upon the often-challenging railway environment, along with radical changes to the national economy during this era had also impacted the type's suitability to these broader circumstances and thus its overall performance.

After withdrawal 23 of the class were stored at the former Ipswich engine shed during 1971 before being hauled away, generally as part of booked freight trains, for scrapping.

[4] The four Class 15s that survived were used for departmental service for a time, for which they were converted into non-powered electric train pre-heating units based at Doncaster Works.

[14][4] A ready to run model in 00 gauge was available from TechCad design based on a hand finished resin shell and powered by a Mashima motor.