Certain of inevitable war with the U.S., Japan launched a preemptive strike that shocked Americans and prompted the nation to enter World War II.
By Erin Blakemore December 6, 2021 • 8 min readMasao Asada had just finished delivering groceries around Pearl Harbor, Oahu, when he heard some huge booms. No big deal, he thought—he was used to hearing noise from dredging activity in the Pacific Ocean lagoon. But the booms kept coming.
Asada jumped in his truck and drove toward the pier used by the U.S. Navy and Army. En route, he was flagged down by the driver of another car. “Get out of here!” the man shouted, Asada recalled in an oral history taken years later. “This is not practice! It’s war.” That’s when Asada looked to the sky and saw Japanese warplanes zooming overhead.
The grocery store owner was one of the thousands of eyewitnesses to Japan’s surprise attack on Pearl Harbor on December 7, 1941—an act of war that, though just 90 minutes long, irrevocably changed the course of world history.
Tensions between Japan and the U.S. simmered throughout the early 20th century and came to a boil in the 1930s as Japan attempted to conquer China, even attacking civilians. In 1937, China and Japan went to war. By 1940, the U.S considered the Japanese expansion into China threatening enough to its interests that it began to provide military aid to China and started to sanction Japan. After Japan signed mutual defense pacts with Nazi Germany, Italy, and the Soviet Union in 1940 and 1941, the U.S. froze Japanese assets and forbade all exports into Japan.
Meanwhile, Nazi Germany continued its conquest of much of Europe. Though the U.S. was officially neutral in both conflicts, its stance was increasingly challenged both by Japan and Nazi Germany’s wars.
Neutrality was the most divisive public issue of its day, and a majority of the American public, which remembered the losses of World War I and was still recovering from the effects of the Great Depression, opposed entering any war overseas. Still, many Americans wanted the nation to help its embattled allies. President Franklin D. Roosevelt accomplished this through the Lend-Lease Program, which provided allies like Great Britain and China with weapons and military equipment.
But as Japan continued its war with China, a conflict with the U.S. became all but inevitable, prompting Japanese leaders to assess their options. The U.S. Navy was formidable, and Japan didn’t have the resources it needed to eliminate the American threat to their imperial ambitions. But they had one trick up their sleeve: surprise. Admiral Yamamoto Isoroku convinced Japan’s military officials that instead of declaring war on the U.S., they should confront them in the Pacific, doing as much damage to the Pacific Fleet as possible.
While mainland U.S. forces mobilized in the wake of a surprise attack, Yamamoto argued, Japan could seize strategic Pacific islands. Japan was desperate for supplies, and the islands that lay between Japan and the furthest U.S. territory in Hawaii could provide much-needed oil and rubber.
Yamamoto spent months patiently planning the operation with naval captain Minoru Genda and others. In December 1941, Japan’s monarch, Hirohito, finally bowed to months of pressure from the military and authorized war.
