 This included the removal of a heavy gun platform the Navy had installed on her forward deck, an overhaul of her engine and other machinery, interior alterations, and the installation of bilge keels, electric lighting, and a dredging winch.Finally ready for fishery service, USFS "Halcyon" made her first scientific cruise in August 1920; conducted at the request of fishing interests in Massachusetts, the cruise covered of fishing grounds in the Gulf of Maine and to the south and southwest of the South Shoal Lightship in an unsuccessful attempt to locate schools of mackerel.She then made two oceanographic cruises in the Gulf of Maine under the direction of Dr. Henry B. Bigelow, the first in December 1920–January 1921 and the second in March 1921, steaming a combined total of between Cape Cod, Massachusetts, and Nova Scotia, Canada.