The Class 20 diesel locomotive, also known as the English Electric Type 1, were built by English Electric at Vulcan Foundry and Robert Stephenson and Hawthorns.
In total, 228 locomotives in the class were built between 1957 and 1968. The large number being in part because of the failure of other early designs in the same power range to provide reliable locomotives. The locomotives were originally numbered D8000–D8199 and D8300–D8327, before they were re-numbered in the BR TOPS scheme. They are also known by their nickname as "Choppers", a name derived from the distinctive beat that the engine produces under load which resembles the sound of a helicopter.
A total of 26 Class 20 locomotives are preserved, including the first of the class built, D8000, which is part of the National Railway Collection at the National Railway Museum in York. They can still be found on departmental duties such as hauling RHTTs.