 Based at the BOF's Boothbay Harbor station from July to October 1921, she underwent an overhaul in July and August 1921.With it completed, she made a cruise between Nantucket, Massachusetts, Browns Bank, and Yarmouth, Nova Scotia, Canada, to collect bottom samples in support of a hydrographic survey of the Gulf of Maine.In October 1921, "Halcyon"s home port changed to the BOF station at Woods Hole, Massachusetts.