December 1941: Japanese attack on Pearl Harbor

What:

Yesterday, December 7th, 1941—a date which will live in infamy—the United States of America was suddenly and deliberately attacked by naval and air forces of the Empire of Japan. The United States was at peace with that nation and, at the solicitation of Japan, was still in conversation with its government and its emperor looking toward the maintenance of peace in the Pacific.  I ask that the Congress declare that since the unprovoked and dastardly attack by Japan on Sunday, December 7th, 1941, a state of war has existed between the United States and the Japanese empire.

Why:

On 1 August 1941, in response to continued Japanese aggression in China and Japan’s invasion of French Indochina, the US embargoed Japan, cutting it off from a crucial oil supply. The only other oil supply, apart from the USA, was held by the Netherlands in their East Indies colony. Japan knew that to continue its war efforts, and to eventually invade the USSR, it needed access to another oil supply. However, invading the East Indies was thought likely to trigger American intervention due to its proximity to the Philippines, which was still an American colony.

The decision to attack the USA was also heavily influenced by competition between the Army and the Navy in Japan. The army had been receiving the vast majority of support and budget during the course of the war in mainland Asia and the navy was jealous. Attacking the USA would start a war in the Pacific that could be dominated by the navy and justify greater political standing and a larger share of the military budget for the branch. The oil embargo provided a pretty good reason to do it.

Pearl Harbor was chosen because it was the primary base for the US Pacific Fleet, one of the two main fleets of the US. If Japan attacked, it knew that this would start a massive and protracted naval war with the USA, in which the US Navy would have an advantage. To offset the material advantage enjoyed by the USA, Japan sought to utterly destroy one of the its fleets in a surprise attack, forcing the US to either rebuild the fleet from scratch or take a long time to transfer ships from the Atlantic.

 

Impact:

The attack on Pearl Harbor was massively important because it involved the USA in WWII. It is likely, considering widespread isolationist feeling in the USA at the time, that the US would never have become involved in WWII, or would have only become involved at a much later date, had Japan not attacked Pearl Harbor. American entry into the war massively boosted the material and military resources of the Allied side, and the USA is almost solely responsible for the defeat of Japan.

The destruction of much of the US Pacific Fleet at Pearl Harbor was as successful as the Japanese had expected, temporarily crippling America’s ability to conduct a war in the Pacific. However, Japan had vastly overestimated the amount of time it would take to replace lost assets. Not reckoning with the size of American industry, Japan had assumed it would take years for the USA to respond. Instead, America had rebuilt large portions of the Pacific Fleet and gone on to expand the navy within only a few months.