Constructed by Sheffield train builders Cravens in response to BR orders for diesel multiple units these units had a distinctive 2-window front end. The units were quickly pressed into suburban service around London, a service for which the design had not been intended, but proved highly successful. Although the design was not perpetuated Cravens built a quality product and the units ran into the 1980s, outlasting many other builders trains. One 2-car set is preserved, having delivered many more years of reliable service in preservation and with a secure future ahead.