HMCS Rainbow was built by the Portsmouth Naval Shipyard in Portsmouth, New Hampshire. Her keel was laid on June 28, 1944. She was launched on October 1, 1944 and commissioned into the United States Navy as USS Argonaut SS475 on January 15, 1945. Argonaut was one of 25 Tench Class Fleet Submarines built by the United States.

Argonaut proceeded to join World War II as part of the Pacific submarine fleet based out of Pearl Harbor, Hawaii. She departed from that port in June of 1945 on what was to be her only war patrol. Under the command of John B. Schmidt, the patrol lasted 52 days, with a patrol area of the East China Sea. At this late time of the war, targets were few and far between. Argonaut still managed to sink a 25-ton cargo junk, bombard a Japanese radio detection finder off the coast of Korea, and rescue a downed Marine Corps fighter pilot.

After the war ended, Argonaut continued service with the United States Atlantic Fleet. She was given the Fleet Snorkel conversion at the Philadelphia Naval Shipyard in 1952, which saw the replacement of her WWII fleet type bridge with a new streamlined sail and snorkel. Unlike the GUPPY conversions, her original superstructure was retained.

In the early 1950's, Argonaut operated out of New London, Connecticut as training boat for the Submarine School located there. In this capacity she would dive and surface several times a day to train new submariners in proper operation of this complex vessel. In May of 1955, she and her sister USS Torsk SS423 were transferred to Squadron 6 in Norfolk, Virginia to participate in operations related to the Regulus Missile Program, then under development. She also took part in exercises with surface ships and aircraft for anti-submarine warfare. The photograph below shows her in a nest alongside a tender in Norfolk in the late 1950's.

On December 2, 1968 Argonaut was decommissioned and sold to the Canadian Navy, where she was renamed Rainbow, and given the pennant number SS 75. She was based on the west coast of Canada, sailing out of Esquimalt (Victoria), British Columbia. She served proudly with the Canadian Navy, providing anti-submarine training services to the surface fleet and maritime patrol aircraft. She also took part in many combined US and Canadian exercises.