Battle of Guam ( 1944 ) The Second Battle of Guam ( July 21 — August 10 , 1944 ) was the American capture of the Japanese held island of Guam , a United States territory ( in the Mariana Islands ) during the Pacific campaign of World War II . Background . Guam is the largest of the Marianas , 30 miles ( 48 km ) long and 9 miles ( 14 km ) wide . It had been a United States possession since its capture from Spain in 1898 until it was captured by the Japanese on December 10 , 1941 , following the Attack on Pearl Harbor . It was not as heavily fortified as the other Mariana Islands such as Saipan that had been Japanese possessions since the end of World War I , but by 1944 it had a large Japanese garrison . The Allied plan for the invasion of the Marianas called for heavy preliminary bombardment , first by carrier aircraft and planes based in the Marshall Islands to the east , then once air superiority was gained , close bombardment by battleships . Guam was chosen as a target because its large size made it suitable as a base for supporting the next stage of operations towards the Philippines , Taiwan and the Ryukyu Islands ; the deep - water harbor at Apra was suitable for the largest ships ; and the two airfields would be suitable for B - 29 Superfortress bombers . The invasion of Saipan was scheduled for June 15 , 1944 , with landings on Guam tentatively set for June 18 . The original timetable was optimistic , however . A large Japanese carrier attack and stubborn resistance by the unexpectedly large garrison on Saipan led to the invasion of Guam being postponed for a month . Battle . Guam , ringed by reefs , cliffs , and heavy surf , presents a formidable challenge for an attacker . But despite the obstacles , on July 21 , the Americans landed on both sides of the Orote peninsula on the western side of Guam , planning to cut off the airfield . The 3rd Marine Division landed near Agana to the north of Orote at 08 : 28 , and the 1st Provisional Marine Brigade landed near Agat to the south . Japanese artillery sank 20 LVT s , and inflicted heavy casualties on the Americans , especially on the 1st Provisional Marine Brigade , but by 09 : 00 men and tanks were ashore at both beaches . The 77th Infantry Division had a more difficult landing . Lacking amphibious vehicles , they had to wade ashore from the edge of the reef where they were dropped by their landing craft . The men stationed in the two beachheads were pinned down by vicious Japanese fire , making initial progress inland quite slow . By nightfall the Americans had established beachhead s about 2 , 000 meters deep . Japanese counter - attacks were made throughout the first few days of the battle , mostly at night , using infiltration tactics . Several times they penetrated the American defenses and were driven back with heavy loss of men and equipment . Lieutenant General Takeshi Takashina was killed on July 28 , and Lieutenant General Hideyoshi Obata took over the command of the defenders . Supply was very difficult for the Americans in the first days of the battle . Landing ships could not come closer than the reef , several hundred yards from the beach , and amphibious vehicles were scarce . However , the two beachheads were joined up on July 25 , and the Orote airfield and Apra harbor were captured by July 30 . The counterattacks against the American beachheads , as well as the fierce fighting , had exhausted the Japanese . At the start of August they were running out of food and ammunition and had only a handful of tanks left . Obata withdrew his troops from the south of Guam , planning to make a stand in the mountainous central and northern part of the island . But with resupply and reinforcement impossible because of American control of the sea and air around Guam , he could hope to do no more than delay the inevitable defeat for a few days . Rain and thick jungle made conditions difficult for the Americans , but after an engagement at Mount Barrigada from August 2 to August 4 , the Japanese line collapsed ; the rest of the battle was a pursuit to the north . As in other battles of the Pacific War , the Japanese refused to surrender , and almost all were killed . On August 10 , after 3 long weeks of bloody and ferocious fighting , organized Japanese resistance ended , and Guam was declared secure . The next day , Obata committed ritual suicide . Aftermath . A few Japanese soldiers held out in the jungle . On December 8 , 1945 , three U . S . Marines were ambushed and killed . On January 24 , 1972 , Sergeant Shoichi Yokoi was discovered by hunters . He had lived alone in a cave for 27 years . After the battle , Guam was turned into a base for Allied operations . Five large airfields were built by the Seabees , and B - 29 bombers flew from the island to attack targets in the Western Pacific and on mainland Japan . Four U . S . Marines were awarded the Medal of Honor for their heroic actions during the Battle of Guam : PFC Luther Skaggs Jr . , PFC Frank Witek ( posthumously ) , PFC Leonard F . Mason ( posthumously ) and Captain ( later General ) Louis H . Wilson , Jr . . Liberation Day continues to be celebrated on Guam every July 21 .