Cobra was built as a private motorboat of the same name at Lynn, Massachusetts, in 1917 at a cost of US$14,000. She had one mast and could accommodate seven passengers and crew.[1]
On 19 September 1917, the U.S. Navy acquired Cobra for use as a section patrol boat during World War I. She was commissioned as USS Cobra (SP-626) on 19 September 1917. Assigned to the 1st Naval District in northern New England, Cobra performed patrol duty for the rest of World War I.
World War I ended on 11 November 1918, and sometime thereafter the Navy decommissioned Cobra. Under an executive order dated 24 May 1919 addressing the disposition of vessels the Navy no longer required, Cobra was among several vessels designated for transfer to the United States Bureau of Fisheries (BOF).[1] The Navy duly transferred her to the BOF on 9 September 1919.
Prior to Cobras official transfer, the Bureau of Fisheries took possession of her at Quincy, Massachusetts, in July 1919 and renamed her USFS Petrel.[1] The BOF vessel USFS Phalarope towed Petrel and another former U.S. Navy patrol boat, the BOF vessel USFS Merganser, from Quincy to the Norfolk Navy Yard in Portsmouth, Virginia.[1] There Petrel and Merganser were loaded aboard the U.S. Navy collier on 3 October 1919.[1] Neptune transported them to the Puget Sound Navy Yard in Bremerton, Washington, arriving there in early 1920.[1] After they were unloaded, Petrel and Merganser were taken to Seattle, Washington, to undergo inspection.[1]
After the inspections were complete, Petrel and Merganser were loaded aboard the Pacific American Fisheries steamer Redwood, which transported them to Kings Cove, Territory of Alaska, where Redwood arrived on 18 June 1920.[1] The BOF intended to use them to conduct fishery patrols in the waters of Alaska, but withheld them from service, and instead sent them back to Seattle for repairs and to modify them for fishery patrol work as funds became available for the repairs and modifications.[1] Petrels modifications took place in early 1922; they involved general remodeling, re-decking, and the replacement of her original 350- Dusenberg engine with a more economical 25hp Standard engine removed from the BOF vessel USFS Auklet when Auklet underwent an engine upgrade.[1] Early in the summer of 1922, Auklet towed Petrel to Wrangell, Territory of Alaska, from which Petrel finally began her annual patrol duties, operating in the waters of Southeast Alaska.[1]
Petrels engine eventually broke down, and she was laid up during the 1926 fishing season.[1] After the installation of a new 50hp, four-cylinder Cummins engine, she resumed her patrol duties on 20 September 1927.[1] During 1930, she was involved in enforcing laws protecting fur seal populations near Sitka, Territory of Alaska.[1]
Petrels last BOF service took place during the 1934 fishing season.[1] At the conclusion of the season, she was decommissioned at Seattle.[1]