[citation needed] MV Glen Sannox was built for the Arran route, replacing the pioneering "A B C ferries", which were struggling to keep up with the demand created by their own success.

After her maiden voyage on 29 June 1957, Greenock Fair Saturday, she spent a few more days receiving finishing touches at Gourock and took up the Arran route on 5 July.

[1] By 1969, when the Scottish Transport Group acquired the Caledonian Steam Packet Company, the Arran service was under serious pressure.

During her life, a stern ramp was added to allow linkspan operation, the crane was removed and the side-ramps were remodelled as well as numerous changes of livery.

[1] MV Glen Sannox was the main ferry on the Ardrossan - Brodick - Fairlie Arran route for several years.

On introduction, she increased the service from two daily return trips to four, lying overnight at Brodick and using Ardrossan as the principal mainland port.

She spent the 1974 season as the Oban - Craignure ferry, but was increasingly bothered with mechanical trouble, requiring a specially manufactured replacement piston.

Back in the Clyde, she spent two years on contract between Wemyss Bay and the McAlpine oil-rig yard at Ardyne.

[1] Destined for Clyde cruising, in place of TS Queen Mary, she underwent a massive refit in 1976/77, but introduction was delayed by service needs.

While awaiting a new ferry, MV Saturn for Rothesay, Glen Sannox took up the Wemyss Bay roster and inaugurated new linkspans there in May and June 1977.

[1] Glen Sannox appeared on many of the CalMac's Clyde and West Highland routes, but never sailed to any of the Outer Hebrides, or even to Skye.

Despite speculation about redeployment to Oban, she remained essential on the Clyde, as the only suitable alternative to the elderly MV Clansman.