The '1^st Battle of Guam' was fought between Japanese and US forces for the US island of Guam in the Mariana islands group (8/10 December 1941).

Guam is the southernmost part of the Mariana islands group in the Pacific Ocean. It is the largest of the islands, with an area of 225 sq miles (582.75 km²). The island’s interior is rugged, with thick tropical forests in the north of the island and wooded hills in the south. Much of the island’s coast is edged with coral reefs and cliffs, though beaches suitable for landing troops exist in the centre of the western coast.  Guam has a tropical climate, though December forms part of the dry season. 

The USA captured Guam from Spain on 21 June 1898 during the Spanish-American War, and in the following year Spain sold the other islands of the Mariana islands group to Germany. The US Navy established a facility near the village of Piti on Guam in 1899, and the US Marine Corps opened a barracks at Sumay in 1901. A naval coaling station was established in 1905, and in 1909 a battery of six 6-in (152-mm cm) guns was emplaced to strengthen Guam’s defences. A US Navy captain served as both the governor and commander of the naval base from 1899 onward, though there were also some elements of a civilian government on the island. During World War I, Japanese forces captured the German-controlled islands in the Marianas group in October 1914, and then established a garrison which was designated as the South Seas, Defence Force. In December 1920, Japan gained a League of Nations mandate over the islands, which were then administered by the South Seas Bureau, part of the Ministry of Overseas Affairs. Japanese colonists were permitted to settle in the Mariana islands group, and by the a time late in the 1930s there were more colonists than natives in the Japanese islands. In 1935 the Japanese government banned Westerners from entering its mandated islands in the Pacific, and in 1939 established the 4^th Fleet to defend the region.

While the USA considered increasing Guam’s defences during and after World War I, no action was taken other than the deployment of a US Marine Corps seaplane unit to the island in 1921. The outcomes of the 1922 Washington Naval Conference included an agreement by both the US and Japanese governments that they would not fortify the islands, including the Marianas group, they administered in the western Pacific. As a result, no further improvements were made to Guam’s defences during the 1920s and 1930s, and the island’s coastal artillery battery had been removed by 1930. The US Marine Corps seaplane unit also departed in the following year. The US Navy sought authorisation to build fortifications on the island in 1938, but this proposal was refused. In 1941 Guam had a population of 23,394, most of whom lived in or within 10 miles (16 km) of Agana, the island’s capital. The island had about 85 miles (137 km) of improved roads and Apra Harbor was considered the best in the Mariana islands group, but Guam had no airfield.

Japanese plans for the forthcoming war in the Pacific included the seizure of Guam in the campaign’s earliest days and, from March 1941, Japanese aircraft flew photo-reconnaissance sorties over the island.  Plans for the invasion of the island were completed in September 1941, and Major General Tomitaro Horii’s South Seas Detachment was selected as the main unit responsible for this. The 4,886-man South Seas Detachment included the 144^th Regiment and other units detached from Lieutenant General Hiroshi Takeuchi’s 55^th Division. The South Seas Detachment was concentrated in Korea during November 1941 and, following a brief stay in Japan, sailed for Chichi-jima in the Bonin islands group late that month. The 370-man 5^th Company of the 2^nd Maizuru Special Naval Landing Force, which was based on Saipan in the Mariana islands group, was also assigned to join the assault on Guam.  These units would be transported to Guam by nine transports escorted by the minelayer Tsugaru and four destroyers. The 6^th Cruiser Division comprising four heavy cruisers, was also available to provide support if needed. The landing force and naval units were supported by the 18^th Naval Air Corps, which was based on Saipan and equipped with obsolete floatplanes.

The US government believed that it would be neither possible nor practical to defend Guam should it come under attack, and the island was not seen as being useful in efforts to reinforce the Philippine islands group, though it served as a refuelling point for Pan Am civilian flying boats and was one of the relay points for the Pacific Cable Company’s telegraph cable which linked the Philippine islands group with the US west coast. In 1941, the island was given a Category F defence rating: this ruled out the construction of new defences and meant that, when war broke out, Guam’s defenders were to destroy all facilities of military value and withdraw.Despite this, and with only small arms available to them, the US Marines stationed on the island under the command of Lieutenant Colonel William K. MacNulty, fortified their positions and put up a defence against the subsequent Japanese aerial assault on the island, while suffering losses and other casualties of nearly one-third of their complement.

Despite the island’s low priority, some minor steps were taken by other commands to improve Guam’s defences before war broke out. A contract for minor improvements to the military facilities on Guam was issued in April 1941, and work began in the following month. The Guam Insular Force Guard, which was a local militia unit responsible for protecting the naval base, was also slightly expanded in May. On 17 October, dependents of US military personnel on the island were evacuated to the USA by the transport Henderson, followed by more than 1,000 construction workers. On 23 October, the US Navy’s General Board provided Secretary of the Navy Frank Knox with a report on Guam’s defences which recommended against reinforcing the island because of the inevitable geographical and logistical difficulties of defending it and the need to allocate resources to other priorities. The report argued in favour of continuing to improve Guam’s harbour and seaplane facilities, however.

At the outbreak of war on what was locally 8 December 1941, Guam was held by small US Navy and US Marine Corps units as well as the Insular Force Guard. Captain George McMillin, who was the island’s governor and the overall commander of the garrison, was in charge of naval forces, which amounted to 271 personnel and four nurses. This force was a subordinate unit of Admiral Thomas C. Hart’s Philippines-based Asiatic Fleet and most of its personnel were unarmed. Guam’s guard ship, Gold Star, had sailed to the Philippine islands group to pick up supplies and enable the crew to buy Christmas presents, and was directed to remain there.  The minesweeper Penguin was present at the island, along with the immobile oil depot ship Robert L. Barnes  and two old yard patrol boats YP-16 and YP-17, which had been delivered aboard the naval replacement oiler Ramapo on 22 October 1940. The strength of the US Marine Corps element was 145 men organised into a company armed with rifles and a small number of machine guns.  The Insular Force Guard comprised 246 men, of whom the majority had received little training. The marines and Insular Force Guard were equipped with 170 M1903 Springfield rifles, 13 Lewis light machine guns and 15 Browning Automatic Rifles. The defenders had no mortars or artillery other than the guns on Penguin. In addition to these military units, the Guam Insular Patrol, which was the island’s police force, had a strength of 80 men armed only with pistols.

At 04.45 on 8 December, the governor of the island, George McMillin, was informed of the attack on Pearl Harbor. At 08.27, Japanese land-based aircraft from Saipan attacked the marine barracks, Piti Navy Yard, Libugon radio station, Standard Oil Company, and the Pan American Hotel. During the air attack, the minesweeper Penguin, which was the largest navy vessel at the island, was sunk after shooting down at least one Japanese aeroplane. One officer was killed and several men wounded. The air raids all over Guam continued into the morning and afternoon before subsiding at 17.00.

At 08.00 on the following day, Japanese air attacks resumed, with no more than nine aircraft attacking at a time. The previous day’s targets were again attacked, as too were th Government House in Agana and several villages. That evening, a Japanese invasion fleet of four heavy cruisers, four destroyers, two gunboats, six submarine chasers, two minesweepers, two destroyer tenders, and 10 transports (Yokohama Maru, China Maru, Cheribin Maru, Clyde Maru, Daifuku Maru, Kogyoku Maru, Matsue Maru, Moji Maru, Nichimei Maru and Venice Maru) departed Saipan for Guam. A mistake in their intelligence gathering had caused the Japanese to overcommit resources and attack Guam with disproportionate force.

The Japanese landed about 400 men of the 5^th Defence Force from Saipan on Guam in the early morning of 10 December at Dungcas beach to the north of Agana. The Japanese attacked and quickly defeated the Insular Force Guard in Agana, and then advanced on Piti, moving toward Sumay and the marine barracks. The principal engagement took place on Agana’s Plaza de Espana at 04.45 when a few marines and Insular Force guardsmen fought with the Japanese naval soldiers. After token post-invasion resistance, the marines, on McMillin’s orders, surrendered at 05.45. McMillin officially surrendered at 06.00. A few skirmishes took place all over the island before news of the surrender spread and the rest of the island’s forces laid down their arms. The patrol boat YP-16 was scuttled by means of fire during the event and YP-17 was captured by Japanese naval forces. A US freighter was damaged by the Japanese.

In the meantime the South Seas Detachment made separate landings at Tumon Bay in the north, on the south-western coast near Merizo, and on the eastern shore of the island at Talofofo Bay.

US Marine losses were five men killed and 13 wounded, figures which include the earlier Japanese air assault of the island. The US Navy lost eight men killed, and four of the Guam Insular Force Guards were killed and 22 others wounded. One Japanese naval soldier was killed and six wounded.

Some 13 US civilians were killed by the Japanese during the battle. Six US Navy sailors evaded capture by the Japanese rather than surrender: five were eventually caught by the Japanese and beheaded. The last of the men survived with the help of Chamorro islanders, who moved him from village to village, sometimes endangering their own families for his protection. The Japanese knew that an unknown American could not hide without some form of help, and as a result Chamorro suspects were questioned, tortured, and beheaded. Despite the abuses, Chamorros loyal to the USA protected the sole American, who managed to endure throughout the 30 months of the Japanese occupation.