Okinawa's 82-day battle killed up to 150,000 civilians, and the projected cost of invading Japan itself directly drove the decision to drop the atomic bomb.
Operation Iceberg, the invasion of Okinawa in April 1945, was the largest amphibious assault in the Pacific war — 541,000 US personnel supported by over 1,300 ships. The island's roughly 107,000 Japanese defenders, reinforced by Okinawan civilians pressed into service, were ordered to fight to the last man.
Japan deployed 1,465 kamikaze aircraft against the invasion fleet — more than in any previous battle. The attacks sank 36 ships and damaged 368 others, killing over 4,900 US sailors. American crews reported watching planes dive into ships around them for days at a time, a form of warfare no training had prepared them for.
The Japanese battleship Yamato — the largest ever built — was sent on a one-way mission to Okinawa with only enough fuel to reach the island. The plan was to beach it and use it as an unsinkable gun battery. US aircraft intercepted and sank it on April 7, killing 2,498 of its 2,700-man crew before it ever arrived.
Fighting on the island itself was among the most brutal of the Pacific war. Japanese defenders used an extensive network of caves and tunnels to grind down advancing Americans over 82 days. US casualties exceeded 12,500 killed and nearly 40,000 wounded — more than in any other Pacific battle.
The civilian death toll was catastrophic. Between 40,000 and 150,000 Okinawan civilians died — killed by combat, by Japanese soldiers who used them as shields, or by mass suicides that Japanese propaganda had convinced many was preferable to American capture. Up to a third of the entire Okinawan population perished.
The projected cost of invading the Japanese home islands — estimated at up to a million American casualties, calculated directly from the Okinawa experience — shaped the decision to use atomic bombs on Hiroshima and Nagasaki. Every casualty figure at Okinawa was, in a sense, an argument for what happened next.