 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 . 
