The British Railways ‘Pilot Scheme’ orders of 1955 included ten English Electric Type 2 diesel-electric locomotives deploying Napier ‘Deltic’ engines. These locomotives, more colloquially known as the ‘Baby Deltics’, were introduced into traffic during 1959 for use on the Eastern Region of British Railways. This book looks at the history of the Class 23s, making extensive use of available but previously unpublished archive material, covering their introduction, technical idiosyncrasies, appearance design and performance. Issues with the original ‘Deltic’ engines were ultimately dealt with via a major rehabilitation exercise during the 1963-65 period; whilst various re-engining options were considered , including a new ‘U’ series English Electric high-speed engine design, the original Napier engines were ultimately retained. The work involved in the whole rehabilitation process is discussed in detail using internal English Electric archive material and forms a central focus of research. The fleet survived intact until 1968, when withdrawal commenced as a direct result of declining traffic levels across the UK, with successive National Traction Plans progressively selecting the less successful, non-standard and ‘numerically-challenged’ classes for removal from traffic. All ten locomotives were withdrawn by March 1971. Individual locomotive histories, allocations, fire and accident incidents, liveries and detail differences, storage and disposals are provided for each locomotive.