It joined by declaring war after the Japanese Attack on the US Fleet at Pearl Harbor.
They intercepted a mesage from Japan to its naval fleet.
The US was thrust into WWII by the Japanese attack on the Fleet at Pearl Harbor.
The United States Pacific Fleet was moored at Pearl Harbor and it would take a major US fleet to defeat the Japanese. The attack was so successful in destroying the US Pacific Fleet that a large portion of the US Atlantic Fleet needed to come from the East coast through the Panama Canal to fight the Japanese in the Pacific.
The attack on Pearl Harbor aimed to cripple the US Pacific fleet. The Japanese were set to sweep into Burma, Malaya, the East Indies, and the Philippines, and were afraid the US fleet would spoil their plans.
The Japanese High Command.
There were none: There were Japanese Batleships in the fleet, but the attack was made by carrier-borne aircraft. There was also submarine attack. An attack by Japanese midget submarines as attacked & destroyed. The Japanese fleet included 2 battleships but they did not participate in the attack.
The US Fleet was not told of such an attack.
December 7, 1941
Almost all of the US Pacific Fleet was moored in Pearl Harbour.
The Japanese rejected the idea of invading the continental US due to the fact that so many civilians owned guns.
The Japanese attack on the US Fleet at Pearl Harbor.