From the mid-1960s, passenger ships such as the "Duke of Lancaster" were gradually being superseded by car ferries. Rather than undertake the expensive option of renewing their entire fleet, British Railways instead began a part-programme of conversion. In order to maintain ferry services whilst these modifications took place, the "Duke of Lancaster"'s duties as a cruise ship ceased. On 25 April 1970 the ship returned to service, having had her main deck rebuilt to accommodate vehicles via a door at her stern. The ship now provided space for 1,200 single-class passengers and 105 cars, with a total cabin accommodation for 400 passengers.