Imperial fleet review — the largest fleet review in Japanese history — in honor of the 2,600th anniversary of the enthronement of the Emperor Jimmu, Japan's legendary first emperor. I-68 was decommissioned and placed in reserve on 19 October 1940. While she was inactive, Submarine Squadron 3 was reassigned to the 6th Fleet on 15 November 1940. She returned to active service on 25 July 1941. By 11 November 1941, Submarine Squadron 3 had been assigned to the 6th Fleet′s Advance Force. That day, the 6th Fleet's commander, Vice Admiral Mitsumi Shimizu, held a meeting with the commanding officers of the submarines of the squadron 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. As Japanese military forces began to deploy for the opening Japanese offensive of the war, I-68 departed Saeki Bay on the coast of Kyushu on 11 November 1941 in company with the submarines , I-69, I-70, I-71, I-72, and I-73 bound for Kwajalein Atoll, which she reached on 20 November 1941. Assigned to support Operation Z, I-68 got underway from Kwajalein on 23 November 1941 and set course for the Hawaiian Islands. While she was en route, 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. World War II First war patrol: Attack on Pearl Harbor By the day of the attack, 7 December 1941, I-68 and the other submarines of Submarine Squadron 3 were on station south of Oahu with orders to attack any ships attempting to sortie from Pearl Harbor. On 8 December, I-68 and I-69 received orders to lay off Pearl Harbor and rescue midget submarine crews who had participated in the attack, but none of the midget submarines returned, and I-68 soon returned to her patrol area. Over the course of several days beginning on 13 December 1941, I-68 was subjected to 21 separate depth-charge attacks, the last attack of which damaged many of her battery cells and flooded her aft torpedo tubes. Her commanding officer,