On this day 75 years ago, the last great battle in human history mercifully came to an end

The Battle of Okinawa had raged since U.S. soldiers and marines of the 10th Army landed on the island's shores back on April 1. Since that date, the largest combined land, sea, and air battle had set the Japanese island ablaze. On June 21, some 81 days later, the island was officially declared secure.

For the 250,000+ Americans involved in the operation, it was the most intense and harrowing experience of their lives. When the smoke finally began to clear over the island, it revealed a scene right out of Dante's Inferno. More than 20,000 U.S. soldiers, sailors, and marines were dead. A further 55,000 were listed as wounded or missing. It was by far the bloodiest battle of the Pacific War and, perhaps, a harbinger of things to come in the inevitable invasion of the Japanese home islands.

For the Japanese, the butcher's bill was even worse. An estimated 110,000 IJA soldiers were killed or committed suicide as the battle went south for them. A further 7,000 IJA soldiers surrendered to the Americans. Hit just as hard were the 300,000 Okinawan civilians who populated the island. It is estimated that as many as 150,000 were killed during the battle.

When added together, the total casualties for the Battle of Okinawa comes to 342,000 killed, wounded, or captured/missing. After the horrendous casualties incurred in the battle, Allied military planners couldn't help but wonder just how great the casualties would be if it came to an invasion of Japan. Some estimated casualties north of one million for the Allies alone.

While no one could possibly know it at the time, U.S. President Harry Truman was hedging his bets that a project, being carried out under the upmost secrecy in the desert of New Mexico, would give him another option to use against the Japanese....