Published 29 Sep 2025
The military presence in the Pacific is significantly influenced by the “island chain strategy,” a concept introduced by John Foster Dulles in 1951. This strategy was designed to encircle the Soviet Union and China with naval bases in the Western Pacific, thereby demonstrating power and restricting their access to the sea. Although it was not a primary focus during the Cold War, this strategy remains crucial for both the United States and China, for the United States, it is integral to its military presence in the Far East, while for China, it is vital for maritime security and is perceived as a method of encirclement by the United States. This strategy underscores the continued importance of geography in military planning and highlights persistent tensions in the region.
The strategy demarcates the Pacific into three principal island chains:
The First Island Chain: This constitutes the initial line of islands from the East Asian coast, encompassing the Kuril Islands, Japan, the Ryukyu Islands, Taiwan, the northern Philippines, and Borneo. This chain functions as a frontline for military defence, the waters west of this chain are shallow, which impacts submarine detection and warfare.
The Second Island Chain: Situated further east, this chain includes Japan’s Bonin and Volcano Islands and the Mariana Islands, with a focus on Guam. It serves as a secondary line of defence for the United States, offering a robust base for logistics and command, and is distanced from the mainland for enhanced protection.
The Third Island Chain: This is the easternmost chain, commencing at the Aleutian Islands and extending south through Hawaii and Oceania to New Zealand. It serves as the primary hub for command and logistics in the Indo-Pacific.
This framework demonstrates that Pacific defence is not merely a collection of isolated bases but a cohesive and strategic network.
The First Island Chain
Japan is a crucial ally and is central to the U.S. presence in the Pacific. The U.S. military operates in Japan under the U.S.-Japan Treaty of Mutual Cooperation and Security of 1960. This has resulted in a substantial long-term U.S. military presence, comprising approximately 60,000 military personnel, 35,000 family members, and 7,000 civilian and contractor employees. This presence encompasses all military branches, reflecting the alliance’s comprehensive nature.
Key U.S. military bases are distributed throughout Japan. The Yokota Air Base near Tokyo serves as the main headquarters for the U.S. Forces Japan. Kadena Air Base on Okinawa is a major Air Force centre and plays a critical role in defence. The U.S. Navy maintains significant facilities at Yokosuka and Sasebo, where vessels such as the USS Ronald Reagan are stationed. The Marine Corps has a substantial presence at Camp S D Butler in Okinawa, which includes several camps and an air station, with approximately 19,500 Marines. Other significant bases, such as the Atsugi and Misawa Air Bases, provide air support.
The strategic significance of the United States military presence in Okinawa is considerable, yet it is constrained by spatial limitations. A plan has been proposed to relocate a portion of the marine forces from Okinawa to Guam. This initiative aims to decrease the concentration of military personnel in Okinawa and redistribute them to a location deemed more secure. This transition reflects a strategic shift towards a more adaptable and less susceptible military configuration.
In South Korea, the United States maintains a substantial military presence through a bilateral agreement, key installations include the U.S. Army Garrison Daegu, and Camp Humphreys. Historically, U.S. forces were dispersed across various locations; however, they are now primarily consolidated at the Camp Humphreys, which has been expanded to nearly 3,500 acres, is the largest U.S. military base overseas and accommodates the United States Forces Korea (USFK) and the United Nations Command Headquarters. It also features a highly active airfield, the consolidation of 28,500 U.S. troops at this extensive base enhances command and control capabilities and positions them at a greater distance from the Demilitarised Zone (DMZ), thereby increasing their resilience to surprise attacks while maintaining their combat readiness.
The United States and the Philippines have renewed their defence collaboration. In 1992, the U.S. closed major bases such as Subic Bay and the Clark Air Base. However, in 2014, the two nations re-engaged through the Enhanced Defence Cooperation Agreement (EDCA), which permits U.S. forces to rotate and construct facilities on Philippine bases, although it does not authorise permanent U.S. bases. Initially, the U.S. was granted access to five locations: the Antonio Bautista Air Base, Cesar Basa Air Base, Benito Ebuen Air Base, Fort Magsaysay, and Lumbia Airport. In April 2023, four additional sites were included: Naval Station Narciso del Rosario, Camp Melchor F. dela Cruz, Lal-lo Airport, and Naval Base Camilo Osias. These new sites are strategically significant because of escalating regional tensions. Three are situated in northern Luzon, facing the Taiwan Strait, and one is located on Balabac Island, facing the South China Sea. This development reflects a strategic and defensive posture. Furthermore, Australia is exploring a similar agreement, indicating a broader interest in collaborative defence efforts beyond the U.S. and the Philippines.
The Second Island Chain
Guam plays a pivotal role in the Pacific defence strategy. It is the only island along the 5,000-mile expanse from Hawaii to Asia that possesses both a secure harbour and sufficient land for large-scale airports. This renders Guam a strategic asset comparable to historical locations such as Gibraltar, Malta, and Singapore. Guam’s control provides access to critical regions: China to the west, Hawaii and North America to the east, Southeast Asia from the north, and Japan from the south. As a U.S. territory, Guam serves as a fortified position that is less susceptible to the political complexities that can affect agreements with other nations.
Guam hosts the Joint Region Marianas, which encompasses the Andersen Air Force Base and Naval Base Guam, Andersen Air Force Base serves as a primary installation for bombers and long-range aircraft and accommodates advanced fighter jets such as the F-35 and F-16. Its mission is to maintain readiness for regional conflict. Naval Base Guam is the most developed naval installation on the island, supporting the U.S. Pacific Fleet and housing significant commands, including Submarine Squadron 15, USS Frank Cable, and USS Emory S. Land.
Guam’s strategic significance is underscored by its dual role as a frontline defence point and a secure, autonomous base. As a U.S. territory, it provides a secure location for critical military assets, including nuclear submarines, long-range bombers, and intelligence centres in the Indo-Pacific region. The relocation of a Marine Corps unit from Okinawa to Guam highlights the emphasis on utilising secure areas for essential military resources, which is vital to current strategic requirements.
The Third Island Chain
Hawaii functions as the principal control and support hub for defence operations in the Indo-Pacific. Situated in the Pacific, it is integral to national defence and serves as a frontline for military operations, it hosts numerous military commands, including the U.S. Indo-Pacific Command (USINDOPACOM) at Camp Smith in Hawaii. Key installations include Joint Base Pearl Harbour-Hickam, which supports naval and air forces and is home to the U.S. Pacific Fleet and U.S. Pacific Air Forces, other significant bases include the Schofield Barracks for the U.S. Army and Marine Corps Base, Hawaii. These bases prioritise command, control, logistics, and research over direct combat. They also contribute to humanitarian aid and disaster relief, thereby strengthening regional partnerships that extend beyond military alliances. This defence strategy employs the Third Island Chain to support forces in the First and Second Island Chains.
Australia: The Southern Partner
The US–Australia alliance is pivotal to the Indo-Pacific strategy, U.S. forces utilise Australian bases through agreements that permit a flexible rotational presence rather than permanent installations. The Marine Rotational Force-Darwin (MRF-D) exemplifies this approach in the Indo-Pacific region since 2012, Marines have been rotating to the Robertson Barracks and RAAF Base Darwin for joint exercises with the Australian Defence Force. This force has expanded from 200 Marines to 2,500 annually by February 2024, demonstrating a robust commitment to this model of defence cooperation.
The MRF-D model illustrates the United States’ transition from maintaining permanent military bases to adopting a more flexible strategy. This approach involves troop rotation, which enhances interoperability with allied forces and eases the political and legal challenges associated with permanent bases. In northern Australia, a strategically significant region adjacent to Southeast Asia, U.S. and Australian forces contribute to deterrence efforts without the necessity of large, permanent installations. This rotational deployment strategy is also being implemented in the Philippines, exemplifying a novel and adaptable approach for the region.
The defence strategy
“You can ensure the safety of your defence if you only hold positions that cannot be attacked.” – Sun Tzu
The defence strategy of the United States and its allies in the Pacific is based on a sophisticated network that extends beyond mere physical bases. This network fulfils several critical functions beyond the accommodation of troops and weaponry, including:
– Domain Awareness and Area Defence with facilities such as radar and interceptor sites which are instrumental for threat detection and neutralisation.
– Maintenance and Repair infrastructure such as naval shipyards and aircraft hangars which ensure the operational readiness of weapons systems.
-Training and Exercises facilities such as the Jungle Warfare Training Centre in Japan and Bradshaw Field in Australia which are pivotal in maintaining force readiness and enhancing collaborative efforts.
-Logistics and Prepositioning: The military strategically positions equipment and supplies throughout the Indo-Pacific region for rapid emergency response, coordinated by the Defence Logistics Agency (DLA). This network maintains connectivity to the U.S. mainland, the DLA Indo-Pacific, headquartered in Hawaii, interfaces with the U.S. Indo-Pacific Command, U.S. Forces Korea, and U.S. Forces Japan. Bases on the U.S. West Coast are also integral, with Naval Base San Diego serving as the primary homeport for the Pacific Fleet. Travis Air Force Base in California is crucial for transporting cargo and personnel across the Pacific. The Military Ocean Terminal Concord (MOTCO) on the West Coast functions as a logistics hub, facilitating the swift movement of supplies to global hotspots. These mainland hubs underscore the U.S. military’s capacity to sustain operations over extended distances. Without this robust network, forward-deployed forces would be unable to operate effectively in a protracted conflict.
An analysis of the available data indicates that the United States and its allies have established a meticulously planned defence architecture in the Pacific Ocean. They are transitioning from a fixed-base model to a more flexible and resilient network to address current global challenges.
The United States has implemented a layered defence system to address this issue. Forces are strategically positioned along the First Island Chain and collaborate closely with Japan, South Korea, and the Philippines, Guam functions as a secure base in the Second Island Chain, Hawaii and Australia serve as pivotal command and logistics centres within the Third Island Chain. This configuration has been designed to be both robust and adaptable.
Alliances are indispensable for operational success, providing access to and sharing defence capabilities. Recent agreements in the Philippines and Australia reflect a shift towards flexible deployments rather than large permanent bases. This strategy enables the United States to enhance its presence and foster partnerships while navigating political and legal complexities.
Investments in and the development of infrastructure underscore the United States’ enduring commitment to the Indo-Pacific region and its allies. The comprehensive network, extending from the military forces stationed along the First Island Chain to the logistical hubs located in the U.S. The West Coast constitutes a robust defence system. This configuration is poised to effectively manage emergencies and fortify regional security.
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