A cataclysm became inevitable in the last months before Hiroshima.
By the summer of 1944, U.S. military power in the Pacific Theater had grown spectacularly. Beginning nine days after the D-Day invasion in France, American forces launched their largest attacks yet against the Japanese-held islands of Saipan on June 15, Guam on July 21, and Tinian on July 24. Situated 1,200 to 1,500 miles south of Japan, the crescent-shaped archipelago known as the Marianas was strategically important to the defense of the Empire, protecting vital shipping lanes from Asia and a widened aerial attack of the homeland.
Over the next sixty days, each of the three islands fell to the Americans. During grueling land and sea campaigns, U.S. forces killed 60,000 Japanese soldiers, sailors, and airmen, while the Japanese inflicted just under 30,000 total casualties on the Americans, killing 5,500.
On June 19 and 20, west of the Marianas in the Philippine Sea, the American and Japanese Navies fought one of the greatest air-sea engagements of World War II, the Battle of the Philippine Sea—also known as “The Great Marianas Turkey Shoot.” In the course of the two-day battle, American aviators decimated their Japanese counterparts, shooting down nearly four hundred aircraft. The additional destruction of three Japanese fleet aircraft carriers forever prevented Japan from using carriers to conduct offensive operations in the war.
The losses also made clear to Japan’s military leaders that there was no chance of victory; their only remaining options would lie within the terms of peace, if the Allies were willing to negotiate. With Japan’s failed defense of the Marianas, the war journal of Imperial Headquarters concluded in July of 1944: