An oddity in the world of the electro diesel, the Class 73 was designed with the Southern Region in mind with a capability of picking up power via a third rail shoe as well as an ability to propel itself via an onboard diesel powerplant.

While the concept of a diesel electric was not new at the introduction of the Class 73, the idea of one that can pick up via a third rail as opposed to a pantograph was. While diesel electrics are semi common in the UK, the electro diesel is less so with only three classes representing the type, the 74, short lived 74 and recently introduced Class 88.

Examples were built in two batches, the first in 1962 and a subsequent run between 1965 and 1967, 49 of the class would be built in all. Confined almost entirely to the South, the locomotives would be introduced under BR before passing to a range of private operators following privatisation. 16 examples of the class have been withdrawn as of 2023, with 10 scrapped and 6 in storage. 6 locomotives have entered preservation and 27 are still in service.

Locomotive 73109 would be introduced as E6015 in January of 1966. After leaving BR service at the onset of privatisation the locomotive would be painted in the Network South East livery and named in honour of the memory of the Battle of Britain. The locomotive would keep this name, albeit in an updated format for the rest of its life. As of 2023, the locomotive is in service with GB Railfreight.