On December 7, 1941 an armada of nine Japanese Imperial Navy destroyers, three submarines, seven tankers and six aircraft carriers carrying 414 military-superior torpedo bombers, dive bombers, high-altitude bombers and fighter planes, arrived at a strike point 230 miles north of Hawaii undetected. Within a two hour period the American Pacific Fleet at Pearl Harbor was severely crippled in a surprise aerial attack that destroyed or damaged 19 U.S. ships, destroyed 169 U.S. Navy and Army Air Corps planes and killed 2403 service members. Days later, Japan virtually eliminated the remaining Allied military power in the Pacific through devastating attacks on U.S. and British territory bases in the Philippines, Guam, Wake, Hong Kong and Malaya.

Through remarkable intelligence failure, the U.S. had significantly underestimated the size, strength and threat of the Japanese military. During the lead-up to the Pearl Harbor attack, Japan amassed the third largest Navy in the world, with more aircraft carriers than the U.S. and with the world’s most capable fighter aircraft.  Japan sought to expand its empire to the entire Pacific Rim for world influence and to self-possess the raw materials, most importantly, Dutch East Indies’ oil, needed to fuel its economy and military. 94% of Japan’s oil was imported, 80% of that from the United States, which by the late 1930’s accounted for nearly 70% of world oil production. Following months of failed negotiations and material sanctions to curtail Japanese conquests, which at the time included Manchuria, eastern China and southern Indochina, the U.S. cut off Japan’s oil supply in July 1941 demanding its troops be removed from conquered territories. The aggressive sanctions angered the Japanese against continued Western interference in its Asian affairs. The sanctions instead pushed Japan to secretly plan massive and crippling surprise attacks against Great Britain’s naval facility in Singapore and American bases in the Philippines and at Pearl Harbor to clear a path for its conquest of the oil-rich Dutch East Indies.

Japan’s calculus in attacking the U.S. was based on real and assumptive American weakness. Following WWI, U.S. interest in its military waned from 4 million to just 119,000 troops in 1935, 460,000 in 1940 due to a powerful isolationist movement in the country. The U.S. Congress was divided in funding the military and the economy was recovering from the Great Depression. By comparison, the Japanese military comprised over 4 million well trained, battle-hardened troops. In 1941, U.S. and Ally military presence in the Pacific region was exceptionally weak, particularly in land and carrier-based air power. America’s seven aircraft carriers were divided across world regions, with only three devoted to the Pacific, compared to Japan’s ten. The militaries of Russia and Great Britain were fully consumed in existential battles in Europe against Nazi Germany. China was isolated with Japan’s blockage of its military supply lines. Japan believed the U.S. would be so weakened by the attack on Pearl Harbor that its military would not recover for 18 months to 2 years, giving Japan time to establish a defensive perimeter of airfields and bases in the Pacific so extensive that it would undermine American’s ability or willingness to counter-attack.  Japan also believed the United States as a democracy would be unwilling to support a protracted war in the face of significant losses.  These assumptions would prove Japan’s downfall. Japan had attacked a country with an industrial base 10 times its own.

On December 8, 1941, the U.S. declared war against Japan. When Japan’s Axis partners, Germany and Italy, followed two days later with war declarations against the U.S., America found itself in a global war.

The attack on Pearl Harbor awoke a “sleeping giant”. In 1941, the U.S. was the world’s industrial, mass production and oil production powerhouse. It rapidly converted its expansive peacetime industries to the war, mass producing ships, planes, military vehicles, weapons and ammunition at a rate that would supply nearly two-thirds of the Allies military needs in both the Europe and Pacific wars. Importantly, American manufacturing dominance would allow the Allies to outlast Japan and Germany in a war of attrition, quickly replenishing lost and expended military hardware at a rate far outpacing that of its enemies. Important also, the U.S. controlled two-thirds of the world’s oil supply, which would securely fuel the massive Allied air and naval campaigns to come. Ignoring America’s manufacturing and oil production advantage was a fatal mistake for both Japan and Germany in their war declarations against the U.S.

The attack on Pearl Harbor also unified and galvanized the American people and its leaders to the war. Some 10 million American men joined the military directly following the attack, nearly 40% voluntarily. The greatly expanded military force would be split between Europe and the Pacific.

By June 1942, Japan achieved its primary conquest goals. Its military had occupied a vast new empire extending from western Alaska in the North Pacific to the Solomon Islands in the South Pacific, including eastern China, Korea, Burma, Thailand, French Indochina, Malaya, the Philippines, Dutch East Indies and New Guinea. Oil and raw materials lost to U.S. sanctions were replaced with captured Malaya and Dutch East Indies sources, now shipped with Japanese tankers and transports to its military industry at home. This was the peak of the Japanese Empire.

The tide turned for Japan’s Pacific dominance the same month, June 1942, at the Battle of Midway. U.S. Navy fighter planes from its three Pacific aircraft carriers ambushed and sank four Japanese carriers near Midway Island. U.S. intelligence decoded elaborate Japanese plans to lure the three Pacific Fleet carriers it missed at Pearl Harbor (were at sea) into a fatal trap clearing the seas for Japanese attacks on U.S. bases at Midway and again in Hawaii.

Between August 1942 and June 1944, the U.S. engaged in a strategy of “island hopping” in which it seized Pacific Islands to sever Japanese supply lines and gain military bases from which to launch succeeding attacks on its march toward Japan. The U.S. Navy, Army, Marines and their Allies coordinated these attacks against Japanese control with heavy losses on both sides, including the battles of Guadalcanal (Solomon Islands), Kwajalein (Marshall Islands), Tuwara (Gilbert Islands) and Peleliu (Palau archipelago Micronesia). These successive battles marked turning points in the war as attrition from loses progressively took its toll on Japan’s military power.

Immediately following the war, 854 Japanese were convicted of war crimes, including heinous prisoner of war crimes at War Crimes Trials held in Yokohama. Downed and captured B-29 airmen were among the brutally treated POWs. In 1949, President Truman abruptly ended the Trials, deciding to make Japan an important ally against the spread of communism in Asia at the beginning of the Cold War. Truman signed a peace treaty with Japan in 1952, granting complete amnesty to all accused not yet serving prison terms. In 1958, all Japanese war crimes prisoners were paroled when the U.S. returned governmental authority back to the Japanese.