The last turbine steamer ordered by British Rail (but not the last to enter service (that honour falling to near sister the Holyhead Ferry 1), the Dover was in fact something of an afterthought for her owners. Having ordered the Holyhead Ferry 1 for the Irish Sea from Hawthorn Leslie on the Tyne it soon became apparent that an additional sailing slot was to become available at Dover. Hawthorn Leslie was approached for a sister but unable to meet the required delivery date the order went to Swan Hunter & Wigham Richardson instead.
She entered service at Dover on 24 June 1965, the first new-build British Rail ship to appear in the recently adopted BR livery of monastral blue hull and black-topped red funnel.
Like her Irish Sea fleetmate, the Dover was hopelessly out of date from the start, being of steam propulsion and fitted only with a stern door, while elsewhere on the English Channel Thoresen Car Ferries had introduced drive through diesel powered tonnage (one of which was later to become the Earl William) complete with bridge control.
Released from the Dover-Boulogne route by the new Vortigern on 31 July 1969 the Dover moved to the Irish Sea, joining her near sister at Holyhead, the Holyhead Ferry I. The partnership was a success, the Dover having a larger car deck capacity, and in 1970 she once again ran from Holyhead, this time for the entire summer season. Sailings to Heysham were also offered from Dun Laoghaire.
Throughout the first half of the 1970s the Dover was to find herself spending more time at Holyhead while the Holyhead Ferry I spent much time at Dover, the latter's capacity for 153 cars being insufficient for the Welsh port's peak seasons.
Like the Holyhead Ferry I the Dover also underwent major surgery from which she emerged in 1977 as a drive through ship renamed the Earl Siward.