of the submarines of Submarine Squadron 3 aboard his flagship, the light cruiser , and his chief of staff briefed them on plans for Operation Z, the upcoming surprise attack on Pearl Harbor in Hawaii. The attack would begin the Pacific campaign and bring Japan and the United States into World War II. I-10 and the submarine were assigned to the 6th Fleet Reconnaissance Unit. As Japanese military forces began to deploy for the opening Japanese offensive of the war, I-10, with an embarked Watanabe E9W1 (Allied reporting name "Slim") floatplane, departed Yokosuka, Japan, on 16 November 1941, with orders to conduct a reconnaissance of areas in the vicinity of Fiji and the Samoan Islands, including Tutuila in American Samoa. She arrived at Kwajalein Atoll in the Marshall Islands on 23 November 1941 to refuel, then proceeded to Fijian waters. Off Viti Levu in the Fiji Islands on 30 November 1941, she launched her floatplane to reconnoiter Suva Bay off Suva. The floatplane′s crew reported sighting no enemy ships at Suva Bay, but it never returned to I-10, and after a fruitless three-day search for it and its crew under radio silence, I-10 gave up the search and reported the loss of her plane and its crew to 6th Fleet headquarters. While I-10 was at sea, she received the message "Climb Mount Niitaka 1208" () from the Combined Fleet on 2 December 1941, indicating that war with the Allies would commence on 8 December 1941 Japan time, which was on 7 December 1941 on the other side of the International Date Line in Hawaii. On 3 December 1941, she conducted a submerged reconnaissance of the harbor at Pago Pago on Tutuila in American Samoa, sighting what she identified as a United States Navy "Astoria-class" heavy cruiser. World War II First war patrol Heading toward Hawaii after leaving the waters around American Samoa, I-10 arrived in a patrol area south of Oahu on 7 December 1941, the day the Japanese attacked Pearl Harbor. On 9 December, she received a report that the submarine had sighted the U.S. Navy aircraft carrier , along with orders to leave her patrol area and join the search for Lexington. While southeast of Hawaii after dark that evening, she fired one torpedo at the Panamanian 4,430-gross register ton motor vessel , which was on a voyage from Suva to Vancouver, British Columbia, Canada, with cargo of