[Includes 2 tables, 3 charts, 21 maps and 88 illustrations] On 3 October 1944 American forces in the Pacific Ocean Areas received a directive to seize positions in the Ryukyu Islands (Nansei Shoto). Okinawa is the most important island of the Ryukyu Group, the threshold of the four main islands of Japan. The decision to invade the Ryukyus signalized the readiness of the United States to penetrate the inner ring of Japanese defenses. For the enemy, failure on Okinawa meant that he must prepare to resist an early invasion of the homeland or surrender. The present volume [Of the United States Army in WWII series] concerns one of the most bitterly fought battles of the Pacific war, in which the Army, the Marine Corps, and the Navy all played a vital part. In order to make the Army's role and the campaign as a whole as intelligible as possible the historians have treated in detail the operations of the Marine Corps units attached to Tenth Army, and have also sketched the contribution of the Navy both in preliminary operations against Okinawa and in the campaign itself. Another characteristic of this as of other volumes on Pacific campaigns is that tactical action is treated on levels lower than those usually presented in the history of operations in the European theaters. The physical limitations of the terrain fought over in the Pacific restricted the number and size of the units which could be employed and brought into sharp focus the operations of regiments, battalions, and smaller units. A wealth of verified material on such operations is available for all theaters, but it is only that of the Pacific which can be used extensively, since in other theaters the actions of smaller units are lost in the broad sweep of great distances and large forces. The description of small-unit action has the merit of giving the nonprofessional reader a fuller record of the nature of the battlefield in modern war, and the professional reader a better insight into troop leading.