Whirlwind fitted out at the Charles L. Seabury Company shipyard, then arrived at New Haven, Connecticut, on 17 August 1917. She soon commenced patrols off the Cornfield Point lightship. Her duties included hailing passing vessels and seeing that they kept within their designated channels and that other section patrol boats were on their stations. She also escorted Allied ships through the nets that guarded those waters. In the course of one of her normal cruises, she prevented the steamer SS Noreg, out of Nova Scotia, Canada, from fouling the antisubmarine net during a heavy squall on 24 August 1917. Early in September 1917 she inspected the 11th Division of the 3rd Naval District's local patrol forces on station in Long Island Sound.