The Battle of Okinawa (April 1-June 22,1945) was the last and largest of the Pacific War. Intending to establish bases for the invasion of mainland Japan, 287,000 troops of the U.S. 10th Army attacked 130,000 soldiers of the Imperial Japanese 32nd Army on April 1, 1945.
The Japanese devised a defensive strategy on Okinawa that differed from their previous tactics of resisting invasion forces on the beaches. Instead, they employed a series of strategic lines across the island with pillboxes and strongpoints within caves and even ancient castles. Interlinked defensive positions were able to survive intensive artillery fire and air strikes, enabling a fierce defense for several weeks. In the bloody battle that ensued, Allied forces had to extinguish each defensive position one by one, often using dynamite or flamethrowers.
In addition, the Japanese made massive suicidal attacks against Allied ships with “Special Attack Force” aircraft (Kamikaze) and deployed their gigantic battleship Yamato to be sacrificed in the battle.
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At the end of the campaign on June 22, casualties were staggering:
>77,000 Japanese soldiers dead
>65,000 Allied casualties (including 14,000 dead)
~100,000 civilian casualties
The American general Simon B. Buckner was killed by artillery fire
The Japanese general Ushijima Mitsuru committed suicide
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Interesting PBS special on tunnels of Okinawa: https://www.pbssocal.org/programs/nazi-mega-weapons/nazi-mega-weapons-wwii-mega-weapons-tunnels-okinawa/