The attack on Pearl Harbor (or Hawaii Operation, Operation Z, as it was called by the Japanese Imperial General Headquarters) was a surprise military strike conducted by the Japanese navy against the United States' naval base at Pearl Harbor, Hawaii, on the morning of Sunday, December 7, 1941 (Hawaiian time, December 8 by Japan Standard Time), later resulting in the United States becoming militarily involved in World War II. It was intended as a preventive action to keep the U.S. Pacific Fleet from influencing the war Japan was planning to wage in Southeast Asia against Britain, the Netherlands, and the United States. The attack consisted of two aerial attack waves totaling 353 aircraft, launched from six Japanese aircraft carriers.
The attack sank four U.S. Navy battleships (two of which were raised and returned to service late in the war) and damaged four more. The Japanese also sank or damaged three cruisers, three destroyers, and one minelayer, destroyed 188 aircraft, and caused personnel losses of 2,402 killed and 1,282 wounded. The power station, shipyard, maintenance, and fuel and torpedo storage facilities, as well as the submarine piers and headquarters building (also home of the intelligence section) were not hit. Japanese losses were minimal, at 29 aircraft and four midget submarines, with 65 servicemen killed or wounded.
The attack was a major engagement of World War II. It occurred before a formal declaration of war and before the last part of a 14-part message was delivered to the State Department in Washington, D.C. The Japanese Embassy in Washington had been instructed to deliver it immediately prior to the scheduled time of the attack in Hawaii. The attack, and especially the surprise nature of it, were both factors in changing U.S. public opinion from an isolationist position to support for direct participation in the war. Germany's prompt declaration of war, unforced by any treaty commitment to Japan, quickly brought the United States into the European Theater as well. Despite numerous historical precedents of unannounced military action, the lack of any formal declaration prior to the attack led President Franklin D. Roosevelt to proclaim "December 7th, 1941 — a date which will live in infamy".