The attack took place on a sunny Sunday morning. A minimal contingent of soldiers was on duty at the time. Most offices on the base were closed and many servicemen were on leave for the weekend. New technology, including the new radar mounted on Opana Point, were in place, manned and functioning at the time of the attack. The incoming Japanese attack planes were detected by the radar and reported, but were mistaken for an incoming group of American planes due from the mainland that morning.

While there were veiled warnings and isolated events of Japanese hostilities in the weeks, days and hours ahead of the attack, no one in command at Pearl Harbor or in Washington, D.C., expected a Japanese attack on Pearl Harbor, especially before war was formally declared. Effective cryptography and successful cryptanalysis were in their infancy at the time. Under-funded, under-manned and under-equipped, cryptanalysts had been ordered to concentrate on Japanese diplomatic traffic, rather than naval messages. The nation would have had a much clearer picture of the Japanese military buildup and, with the warning provided by those messages, might have prevented the disaster of Pearl Harbor.

About 360 Japanese attack planes had launched at dawn from aircraft carriers in an attack force of about 33 ships, under the command of Vice-Admiral Chuichi Nagumo. The strike force had steamed, under the cover of darkness, to about 275 to 200 miles north of Oahu. Once the bombers sighted the island, they split into two groups. One group proceeded overland at low altitude across the island and the other flew over the water around the island to make an approach from the south. At 7:55 a.m., the first bombs and torpedoes were dropped. After two hours, the U.S. sustained 18 ships sunk or severely damaged, about 170 aircraft destroyed, and there were about 3,700 casualties. Japanese casualties were minimal.