Guam was not captured by America.
The Second Battle of Guam ( 21 July -- 10 August 1944 ) was the American recapture of the Japanese-held island of Guam , a U.S. territory in the Mariana Islands captured by the Japanese from the U.S. in the 1941 First Battle of Guam during the Pacific campaign of World War II . Guam . On December 7 , 1941 , hours after the attack on Pearl Harbor , Guam was captured by the Japanese , who occupied the island for thirty months . Guam endured hostilities when American forces recaptured the island on July 21 , 1944 ; Liberation Day commemorates the victory .