Petaluma was launched on 5 May 1945, and was about 85% complete when, due to the end of World War II, the ship's US Navy reassignment was canceled. Although initially restored to her original name of Avoca by her original owners, the unfinished ship was completed by the Maryland Drydock Company in Baltimore, Maryland, in October 1947, and sold to the National Petroleum Transport Corporation where she was renamed Transpet.[5][3]
On 29 October 1951, the tanker departed Montreal for Halifax, loaded with 1,500,000 imperial gallons (6,800,000 L) of gasoline and kerosene.[6][7] The following day, the ship suffered an explosion in the engine room while in the Gulf of St. Lawrence. Two seamen were killed in the blast; the other eighteen members of the crew abandoned the sinking ship and were rescued by the British ship Ottinge and landed at North Sydney, Nova Scotia.[6]
In May 1954, the Minneapolis-Honeywell Regulator Company announced that its "sea scanar" device had located the wreck of Transpet at a depth of 120 feet (37 m) about 13 nautical miles (24 km) off Miscou Island. It was the first time the "sea scanar", which had been in use as a fish finder off the West Coast of the United States, had been used in a salvage operation and the first wreck located using it.[7]
