On the morning of 7 December 1941, "Chew" was moored in Berth X-5, alongside "Allen" and the decommissioned , which was being used for storage. At the outbreak of the attack on Pearl Harbor by the Empire of Japan that morning, "Chew" brought one of her 3"/23 caliber guns online and began firing at 08:03, under the command of her executive officer. At 08:11, two of her .50 caliber machine guns were also brought online and began firing. The gun scored one Japanese aircraft shot down and two damaged, and the machine guns observed no hits. "Chew" maintained continuous fire from these weapons until 09:34, when the last of the Japanese aircraft departed. She then got underway and began patrolling for Japanese submarine activity, just southwest of the port entrance buoy. She pinged eight possible contacts and dropped 28 depth charges, which her commander, H. R. Hummer, Jr., reported two Japanese submarines destroyed. Subsequent evidence does not suggest "Chew" struck any Japanese submarines. In the chaos of the attack, a number of "Chew" crew members also disembarked and came aboard nearby battleship , which was in drydock, to assist in manning guns, forming ammunition trains, and fighting fires. Aboard "Pennsylvania", two "Chew" crewman were killed in defending the ship, Seaman Second Class Matthew J. Agola and Fireman Third Class Clarence A. Wise.