P&O Scottish Ferries
P&O took over the routes from the long-established North of Scotland, Orkney & Shetland Steam Navigation Company in 1971. They branded their services "P&O Ferries" from 1975 to 1989 and "P&O Scottish Ferries" thereafter.
The services were taken over by NorthLink Orkney and Shetland Ferries in 2002.
In keeping with the tradition of the company which preceded them on the route, their vessels were (with one or two exceptions) named after saints, such as the St Clair and the St Magnus.
At the end of operations in 2002, the company had four vessels covering the routes:
- Deayton, Alistair (2002). Orkney & Shetland Steamers. Stroud: Tempus Publishing Ltd.
- Cowsill, Miles; Smith, Colin (2010). Passage to the Northern Isles: Ferry Services to Orkney and Shetland 1790-2010 (2nd rev. ed.). Ramsey, Isle of Man: Ferry Publications. ISBN 9781906608149.