[9] Departing Sydney on 16 July using only one engine to conserve fuel, Marion headed through the Strait of Belle Isle and began her oceanographic survey mission.

Initially, only Smith and his executive officer, Lieutenant Noble Ricketts, had the knowledge of how to sample the Arctic waters for temperature and salinity but they trained additional men to handle the instruments used for the survey.

Samples were taken along the coast of Baffin Island and a 450 mi (720 km) line across Davis Strait during the month of August ending at Ivigtut, the site of a cryolite mine that was Greenland's main source of income during that period.

After re-provisioning and fueling, she headed back to sea only to be forced to shelter under Mount Kungmat for three days before departing Cape Farewell on a 620 mi (1,000 km) station line to Belle Isle.

Heavy pack ice along the Newfoundland and Labrador shelf waters prevented icebergs from being carried to shore and forced them to enter shipping lanes to the south.

[12] Since Marion had originally been designed specifically for prohibition enforcement service, after the specialized oceanographic equipment was removed she resumed Rum Patrol duty with a home-port of New London.

With the end of prohibition, she assumed a more traditional role of a Coast Guard cutter, that of search and rescue, law enforcement, merchant vessel inspection, and defense training.

[1] Marion served on anti-submarine patrols with the Navy's Caribbean Sea Frontier Squadron based at Charlotte Amalie during World War II.

On 14 October 1943, off Mayaguez, Puerto Rico, she assisted with the evacuation of the crew of EM Dow which had been badly damaged by squalls on a passage from Baltimore, Maryland.

[1][Note 2] Marion was released from Navy service on 1 January 1946 and was reassigned duties out of Norfolk consisting of law enforcement and search and rescue work.