The Battle of Guam (21 July – 10 August 1944) was the American recapture of the Japanese-held island of Guam, an American territory in the Mariana Islands captured by the Japanese in the First Battle of Guam in 1941 during the Pacific campaign of World War II. The battle was a critical component of Operation Forager. The recapture of Guam and the broader Mariana and Palau Islands campaign resulted in the destruction of much of Japan's naval air power and allowed the United States to establish large airbases from which it could bomb the Japanese home islands with its new strategic bomber, the Boeing B-29 Superfortress.
The invasion of Saipan was scheduled for 15 June 1944, with landings on Guam tentatively set for just three days later, but the Battle of the Philippine Sea and stubborn resistance by the unexpectedly large Japanese garrison on Saipan led to the invasion of Guam being postponed for over a month. On 21 July, American forces landed on both sides of the Orote Peninsula on the western side of Guam, planning to secure Apra Harbor. The 3rd Marine Division landed at Asan near Agana to the north of Orote, and the 1st Provisional Marine Brigade landed near Agat to the south. The Marines at the two beachheads were pinned down by heavy Japanese fire, making initial progress inland quite slow. Supply was very difficult; landing ships could not come closer than the reef, several hundred yards from the beach, and amphibious vehicles were scarce.
The 1st Provisional Brigade blocked off the Orote Peninsula on 25 July, and that night the Japanese counterattacked, in coordination with an attack against the 3rd Marine Division to the north. The effort was a failure. On 28 July the two beachheads were linked, and by 29 July the Americans had secured the Orote peninsula. The Japanese counterattacks against the beachheads and the fierce fighting beforehand had exhausted them. By the start of August, they were running out of food and ammunition, and they had only a handful of tanks left. They withdrew from southern Guam, planning to make a stand in the mountainous central and northern part of the island, and to engage in a delaying action.
The Marines and the Army's 77th Infantry Division overran the rest of the island. Rain and thick jungle made conditions difficult for the Americans, but after an engagement with the main Japanese line of defense around Mount Barrigada from 2 to 4 August, the Japanese line collapsed. On 10 August organized Japanese resistance ended, and Guam was declared secure, but 7,500 Japanese soldiers were estimated to still be at large.
Geography
Guam, at 225 square miles (580 km2), is the largest of the Mariana Islands, larger than the other fourteen major islands combined. It is 32 miles (51 km) long from north to south, with a width ranging from 4 to 10 miles (6.4 to 16.1 km) at different points of the island. Along with the other Mariana Islands, Guam was claimed for Spain by Miguel López de Legazpi on 26 January 1565. It became a United States possession after its capture from Spain in June 1898 during the Spanish-American War. Two months later, Spain ceded Guam and the Philippines to the United States for $20 million (equivalent to about $800 million in 2025), and the island became an unincorporated territory. The island was captured by the Japanese on 10 December 1941, following the attack on Pearl Harbor that brought the United States into World War II.
The island is surrounded by coral reefs varying from 20 to 700 yards (18 to 640 m) wide. The northern coastline is fringed with 100-to-600-foot (30 to 183 m) cliffs. Beyond is a limestone plateau, broken up by three hills, Mounts Barrigada, Santa Rosa and Machanao. The southern part of the island is also fringed with reefs and cliffs, but there are breaks in the reefs and the cliffs are lower. The highest peak is Mount Lamlam near the south west coast. Running north of it are Mount Alifan, Tenjo, Chachao and Aluyom. The best beaches lie in between, around Apra Harbor and Agat Bay.
Before the war, the harbor was used by United States Navy and PanAm seaplanes; there were no airfields before the Japanese occupation. The Japanese built a 4,500-foot (1,400 m) airfield on the Orote Peninsula, and a 5,000-foot (1,500 m) airfield east of the capital Agana was nearing completion in July 1944. Work on a third airfield at Dededo had not progressed any further than the area being cleared and staked out. The average temperature was about 87 °F (31 °C) and humidity was 90 percent, with daily rainfall during the rainy season that usually ran from July to November. In these months, the unpaved roads became all but impassable. Typhoons were not an annual occurrence, but could be devastating; a typhoon in 1900 destroyed most of the crops on the island, and Guam had not fully recovered from a typhoon in 1940.
The population of Guam in 1941 was about 23,400, of whom 21,500 were Chamorro people, the indigenous people of the Mariana Islands, who were United States nationals, but not citizens. The garrison consisted of 400 United States Marine Corps and Navy personnel. Most of the population, about 12,500 people, lived in Agana. On 10 December 1941, just days after the outbreak of the Pacific War, the Japanese invaded Guam. After a short battle, the garrison surrendered. The Americans on Guam were taken to Japan. The diplomats and five Navy nurses were repatriated to the United States in August 1942; the rest remained prisoners of war for the duration. Six American sailors initially evaded capture; five were found and executed, but one, George Tweed, remained at large.
The Chamorro population suffered considerably during the Japanese occupation of Guam. When it became clear the island would soon be invaded, Japanese soldiers committed numerous atrocities. For security reasons, they forcibly relocated most of the island's population to internment camps in eastern and southern Guam, most notably Manenggon, which lacked food, shelter or sanitation. This saved them from the American preliminary bombardment of the island, although that was not the intent.
Strategy
American
After World War I, the United States had developed a series of contingency plans for the event of a war with Japan known as the Orange plans. These envisaged an advance through the Marshall and Caroline Islands to the Philippines, from whence Japan could be blockaded. The Mariana Islands figured only incidentally in the plans, as they lay north of the direct route between Hawaii and the Philippines. During World War II, the islands attracted the attention of naval and air strategists. At the Casablanca Conference in January 1943, the US and British Combined Chiefs of Staff endorsed a Central Pacific offensive along the lines envisaged in the Orange plans. In his formulation of a Pacific strategy, the Commander in Chief, United States Fleet, Admiral Ernest J. King, specifically mentioned the Mariana Islands as "the key to the situation because of their location on the Japanese line of communication."
King envisaged the Marianas primarily as a naval base, especially for submarines, but another rationale for their capture emerged with the development of the long-range Boeing B-29 Superfortress bomber. From the Mariana Islands, B-29s could reach the most significant industrial targets in Japan, and the air staff planners began incorporating the islands into their long-range plans in September 1943. Commander in Chief, Pacific Ocean Areas (CINCPOA), Admiral Chester W. Nimitz, produced a campaign plan called Operation Granite, which tentatively scheduled the capture of the Mariana Islands of Saipan, Tinian and Guam for 15 November 1944.
By February 1944, there was consideration of advancing the timetable by bypassing Truk and heading directly for Palau or the Marianas after the capture of the Marshall Islands. On 7 March, Nimitz and his Deputy Chief of Staff, Rear Admiral Forrest P. Sherman, met with the Joint Chiefs of Staff in Washington, D.C., where they were questioned by the Chief of Staff of the United States Army, General George C. Marshall, and the Chief of Staff to the Commander in Chief, Admiral William D. Leahy. Sherman argued the neutralization of Truk required the occupation of the Mariana Islands to cut the air route to Truk from Japan. On 12 March, the Joint Chiefs directed Nimitz to neutralize Truk and occupy the Mariana Islands, with a target date of 15 June 1944.
Although Saipan and Tinian were more suitable as long-range bomber bases, since they were closer to Japan, Guam was the most desirable of the Mariana Islands for a naval base, because it had a more adequate water supply and the best anchorage in Apra Harbor. It was decided to invade Saipan first, though, because aircraft based there could then protect Tinian and Guam from air attacks from Japan staging through the Nanpō Islands. The operation to capture the Marianas was codenamed Operation Forager; Guam was codenamed "Stevedore".
Japanese
On 30 September 1943, the Japanese Imperial War Council established an "Absolute National Defense Zone" that included the Kuril Islands, Bonin Islands, Marianas, Caroline Islands, Western New Guinea, Netherlands East Indies and Burma. Possession of this area was considered vital, as it gave Japan access to interior lines and provided the food and raw materials needed to sustain Japan's war effort. The Army expressed confidence that the national defense zone could be held, but the Chief of the Imperial Japanese Navy General Staff, Admiral Osami Nagano, was much less certain. The Imperial Japanese Navy planned to hold the national defense zone by defeating the United States fleet in a decisive battle.
Opposing forces
United States
Overall command of the operation was exercised by Nimitz through the commander of the Fifth Fleet, Admiral Raymond A. Spruance. Under Spruance was the commander of the Joint Expeditionary Force (Task Force 51), Vice Admiral Richmond K. Turner; and the commander of the Expeditionary Troops (Task Force 56), Lieutenant General Holland M. Smith. Task Force 51 was divided into the Northern Attack Force (Task Force 52), under Turner, which would land and support the troops on Saipan and Tinian, and the Southern Attack Force (Task Force 53), under Rear Admiral Richard L. Conolly, the commander of Amphibious Group 3, which would land and support the troops on Guam. In addition to the two defense battalions, Brigadier General Pedro Augusto del Valle's III Amphibious Corps Artillery had the 1st and 2nd 155 mm Howitzer Battalions and the 7th 155 mm Gun Battalion. A Marine Corps observation squadron, VMO-1, was also assigned.
In Nimitz's preliminary order of 20 March 1944, the task of recapturing Guam was assigned to Major General Roy S. Geiger's I Marine Amphibious Corps, which was renamed the III Amphibious Corps on 15 April. For this operation, Geiger had the 3rd Marine Division, the 1st Provisional Marine Brigade and the 9th and 14th Defense Battalions. The 3rd Marine Division was commanded by Major General Allen H. Turnage. The 1st Provisional Marine Brigade was activated at Pearl Harbor on 22 March, and Brigadier General Lemuel C. Shepherd Jr. assumed command on 16 April. The brigade was built around the 4th Marine Regiment on Emirau and the 22nd Marine Regiment, which was in the Marshall Islands; both were ordered to move to Guadalcanal. The 27th Infantry Division was designated the reserve for both the Northern and Southern Attack Forces. The Pacific Ocean Areas reserve was the 77th Infantry Division, which was still in the United States, but under orders to move to Hawaii.
Geiger's headquarters was on Guadalcanal in the Solomon Islands, so he flew to Pearl Harbor on 29 March with members of his staff to confer with Spruance, Turner, Smith and Conolly. The plan they drew up, Operation Plan (OpPlan) 1-44, was approved by Smith on 3 April and Turner and Spruance the following day. It called for simultaneous landings on either side of the Orote Peninsula, with a northern attack group commanded by Conolly landing the 3rd Marine Division between Adelup Point and the Tatgua River, while a southern attack group under Rear Admiral Lawrence F. Reifsnider landed the 1st Provisional Marine Brigade on the beaches between Agat and Bangi Point. The vital Orote Peninsula and Apra Harbor area would be seized by a double envelopment. That the area was likely to be heavily defended was not overlooked, but in the Battle of Munda Point the tactic of landing elsewhere and fighting through the jungle to the objective had proved to be both slow and costly. Geiger returned to Guadalcanal on 7 April, and Conolly joined him there eight days later, co-locating his headquarters with Geiger's until the command ship USS Appalachian arrived from Pearl Harbor on 27 April.
In addition to the main plan, two alternative plans were developed to cover the contingencies where one of the beaches was found to be too heavily defended or otherwise unsuitable. OpPlan 3-44 provided for landing the entire force in the south between Agat and Facpi Point, while OpPlan 4-44 provided for the 1st Provisional Marine Brigade to land further south, between Bangi and Facpi Points. The landing date, codenamed W-Day to avoid confusion with Saipan's D-Day, was tentatively set for 18 June, three days after the landing on Saipan.
Considering that Guam had been an American possession for over forty years, the quality of information available to the American forces about Guam was poor. The Office of Naval Intelligence compiled a 345-page study that was issued in February 1944. The 1:20,000 map issued to the troops contained many broken contour lines, indicating the area had not been properly surveyed, and the location of roads and tracks, particularly in northern Guam, was frequently inaccurate. Areas marked bare on the maps turned out to be densely forested, and many low hills were not marked. The Japanese defenders had better maps. Aerial photography was undertaken in April, May and June, but persistent cloud cover left many gaps. Offshore, there was uncertainty about how sharply the reefs dropped off on the seaward side. In April, the submarine USS Greenling took a series of oblique images of the beaches. Plaster 1:5000 relief maps with a 2:1 vertical exaggeration of the beach areas were also prepared. When Conolly issued his operation plan for the assault on 17 May, US intelligence estimated there were between 6,900 and 9,300 Japanese troops of Guam, of whom 2,000 to 2,600 were in airfield construction units.