The ship's assignment at the beginning of the Pacific War was to support the invasion of the Philippines, initially by attacking the American naval base at Davao, Mindanao, on the morning of 8 December. Her air group had not changed, but four of each type of aircraft were spares. "Ryūjō"s initial airstrike consisted of 13 B5Ns escorted by nine A5Ms with a smaller, airstrike later in the day by two B5Ns and three A5Ms. They accomplished little, destroying two Consolidated PBY seaplanes on the ground for the loss of one B5N and A5M. The ship covered the landing at Davao on 20 December and her B5Ns attacked a British oil tanker south of Davao. In January 1942 her aircraft supported Japanese operations in the Malay Peninsula.