Ordered from John I. Thornycroft & Company and built at their Woolston shipyards, she was launched, on 11 November 1965, by the Governor of the Isle of Wight, Lady Brabourne, daughter of Lord Mountbatten of Burma.

[2] Two Crossley Premier diesel engines driving twin screws gave her a maximum speed of 12 kn (22 km/h; 14 mph).

Before this, she occasionally had trouble berthing at Southampton in high winds and was often assisted by the small tug, Bonchurch.

[1] In addition to her normal service operations, Cowes Castle undertook charter cruises, along with her sister ships.

[2] On 11 February 1971, arriving at Southampton in thick fog, she collided with the pontoon and ripped away one of the flotation tanks.