Special narrow bodied diesel electric multiple units were introduced in 1957–58 to replace steam traction. British Rail Class 201 (6S), 202 (6L) and 203 (6B) (the "Hastings Diesels") took over working the route. These units were constructed of narrow rolling stock. They were delivered in six-car formations (the 6Bs including a buffet car) and two units were often operated in multiple to form twelve-car trains. In latter years some of the units were reduced to five, and later still, to four cars.