In late October 1944, del Valle succeeded Major General William Rupertus as Commanding General of the 1st Marine Division, being personally greeted to his new command by Colonel Lewis Burwell "Chesty" Puller. At the time, the 1st Marine Division was training on the island of Pavuvu for the invasion of Okinawa. On May 29, 1945, del Valle participated in one of the most important events that led to victory in Okinawa. After five weeks of fighting, del Valle ordered Company A of the 1st Battalion 5th Marines to capture Shuri Castle, a medieval fortress of the ancient Ryukyuan kings. Seizure of Shuri Castle represented a morale blow for the Japanese and was a milestone in the Okinawa campaign. The fighting in Okinawa would continue for 24 more days. Del Valle was awarded a Distinguished Service Medal for his leadership during the battle and the subsequent occupation and reorganization of Okinawa.