pleasure craft got underway for her maiden wartime patrol, which she conducted in waters off the McCrie Shoal Buoy. During her second patrol, (18 to 20 July) she received information by wireless of enemy submarine activity near New York Harbor and promptly loaded her three-pounder to be ready for action. She soon received a signal from to patrol toward the McCrie Shoal for a distance of 10 miles in search of the U-boat reported in their vicinity. In the pre-dawn darkness on 20 July, Avenger drew within hailing distance of Emerald and received oral orders to instruct all northbound vessels to "hug the coast" because of the U-boats operating to seaward. In accordance with those orders, Avenger hailed a steamer at 0210 on the 20th and warned that Portland-bound vessel of her danger. Avenger's third patrol (22 to 24 July) took her to waters off Atlantic City, New Jersey. When her fourth (26 to 28 July) took her across Delaware Bay to Lewes, Delaware, she sported a new weapon – three depth charges. The fifth (29 July to 1 August) again took her to patrol the shipping lanes off Atlantic City. At 0825 on 7 August, Avenger had just commenced escorting a submarine when a muffler exploded on board. The damage apparently not severe enough to force the craft to curtail her assigned tasks, Avenger returned to Cape May that afternoon, remaining alongside the Fish Dock there until 12 August when she got underway, at the end of a towline, bound for Essington, Pennsylvania. Docking on the 13th, Avenger consequently underwent repairs to her hull and engines at Essington – a spell of yard work that lasted into early October 1918. During that time, so that her crew would not get "rusty" on their weapons, they conducted rifle and machine gun practice at the local yacht club rifle range. After her post-repair trial trip to Marcus Hook and back on 9 October, and her second (record) trial trip to Wilmington, Delaware, and return, Avenger returned briefly to Essington before moving back to her home base, Cape May, on the afternoon of 25 October. Underway the next morning, she patrolled off Cape May on the 28th and into the next day, when she was relieved on station by . Avenger underwent further repairs to her engines (30 October to 2 November) before she departed the Fish Dock, Cape May, at 0955