Reconsidering the Purpose of the Pearl Harbor Attack: Evidence from Yamamoto Isoroku's Letter to Onishi and His 1942 Commendation to the Kido Butai

The Pearl Harbor attack has frequently been interpreted as an attempt to shock the American public into abandoning the will to fight and thereby compel an early settlement. However, the extent to which this interpretation is supported by Admiral Isoroku Yamamoto's own writings remains unclear. This research note examines two primary sources associated with Yamamoto: his January 1941 correspondence concerning the proposed attack and his commendation to the Kido Butai issued on 15 April 1942. Both documents characterize the operation primarily in military and operational terms. The prewar correspondence emphasizes preventing the advance of the United States Fleet into the Western Pacific, while the post-operation commendation praises Pearl Harbor for its contribution to subsequent operations. Neither document explicitly identifies the collapse of American morale as an operational objective. These findings suggest that a reexamination of conventional interpretations is warranted.