[7] As of 2023[update],[9] the John Cabot participated in the deepest submarine rescue ever performed, in 1973, retrieving Pisces III from the seafloor at 480 m (1,570 ft) and rescuing the crew of Roger Mallinson and Roger Chapman.

[13][8] On entry to service it was the only icebreaking cable repair ship in the world, and the first such to be built.

[13][8] In 1965 and 1966, the John Cabot repaired the submarine cable connecting Thule Air Base in Greenland to the rest of the world.

[17][18] For the efforts in repairing the telecommunications cable in November 1965, the ship's captain, Captain George S. Burdock, was awarded the Shield of NORAD in a ceremony on board CCGS John Cabot, while at dock in the Port of Montreal on 22 July 1966.

[19] The John Cabot was one of the ships involved in laying the TAT-5 and SF System transatlantic cables in the 1960s.

[15] In 1985, the ship participated in the search for Air India Flight 182, and its underwater investigation and debris recovery.

[24] The ship successfully retrieved the airplane's black boxes from the seafloor at 2,000 m (6,600 ft) deep.