Overview and Implications of the “Golden Dome” Missile Defense Plan for the U.S. Mainland

“Golden Dome for America”[1] is a cross-border, next-generation missile defense concept announced by US President Trump to protect the US mainland.[2] It essentially extends beyond traditional ballistic missile defense (BMD) with the aim to counter emerging airborne threats[3] such as hypersonic glide vehicles (HGVs), cruise missiles, AI-equipped drone swarms numbering in the hundreds[4]—reflecting the diversifying and increasingly complex nature of these aerial threats as part of an Integrated Air and Missile Defense (IAMD) system.

At the core of this system lies a so-called“System of Systems”[5], which organically integrates technology-intensive, independent detection and tracking sensors, interceptor systems, and command and control networks. Realizing such a system would require national-level efforts comparable to the Apollo program[6], which successfully sent humans to the moon in the 1960s. As airborne threats continue to grow in complexity and accelerate across Asia[7], Japan now faces the critical challenge of aligning its IAMD policy with the United States’new homeland defense initiatives.

Transforming Airborne Threats

Recent airborne threats have undergone remarkable evolution in terms of speed, trajectory, and launch characteristics. In particular, China and Russia’s hypersonic weapons and Fractional Orbital Bombardment System (FOBS)[8] are feared to surpass the design capabilities of existing Ballistic Missile Defense (BMD) systems, potentially rendering their air defense shields ineffective. On the other hand, in 2024, Iran launched a saturation attack[9] involving hundreds of missiles against Israel. Israel successfully responded using a multi-layered air defense system that included the low-altitude missile defense system“Iron Dome,”[10] which once again highlighted the importance of missile defense systems capable of comprehensively protecting the homeland from increasingly diverse and complex airborne threats[11].

In addition to its existing BMD assets[12], the United States is developing a detection and tracking system using space-based hypersonic sensors (Hypersonic and Ballistic Tracking Space Sensor: HBTSS)[13] and satellite constellations[14] (Proliferated Warfighter Space Architecture: PWSA)[15], while also planning to upgrade its Ground-based Midcourse Defense (GMD) through the introduction of Glide Phase Interceptors (GPI). The integration of these existing and under-development defense systems into a unified system aims to achieve an autonomous air defense shield capable of intercepting ballistic missiles and other threats at all stages: immediately after launch (boost phase), during inertial flight outside the atmosphere (midcourse phase), and after re-entry into the atmosphere (terminal phase)[16].

Expectations and Concerns

Promoting the Golden Dome Initiative will enable effective responses to hypersonic weapons and complex saturation attacks that were difficult to counter with conventional missile defense systems, thus improving mainland defense capabilities. On the other hand, some experts argue that lessons should be drawn from the history of the Strategic Defense Initiative (SDI), also known as the “Star Wars program,” proposed by President Reagan but never realized due to various reasons[17]. In particular, it is anticipated that the development and deployment of numerous interceptor systems in low Earth orbit(LEO) will be necessary to intercept ICBMs immediately after launch, and that the construction of a large-scale tracking sensor network will be required to manage intercept operations[18]. Consequently, concerns are growing over the enormous costs associated with these efforts[19].

On the other hand, there is also optimism that integrating cutting-edge fields such as space technology, AI, and quantum communication will accelerate technological innovation in the United States, enhance the superiority of U.S. military power[20], and yield spillover benefits in the civilian sector. This expectation mirrors the legacy of the Apollo program, which spurred advancements in civilian technology. At the system level, the integration of systems requires not only extremely advanced technology and IT infrastructure, but also cross-organizational, functional, and domain-level coordination capabilities to integrate various air defense-related systems—capabilities that include space-based interception, real-time information sharing, and AI-driven command and control[21].

Additionally, the deployment of the Golden Dome could also inadvertently encourage the proliferation of weapons of mass destruction by undermining the reliability of existing airborne threats and increasing the cost-effectiveness challenges for potential attackers[22]. As a result, the United States would need to intensify efforts toward arms control and disarmament concurrent with the development of this system. In this context, this approach reflects lessons drawn from the Reagan era, during which the simultaneous pursuit of missile defense under the SDI and the development of new ICBMs (MX) and single-warhead small ICBMs ultimately contributed to the negotiation of major arms control agreements, including the Intermediate-Range Nuclear Forces Treaty (INF) and the Strategic Arms Reduction Treaty (START)[23]. Building on this precedent, the Trump administration appears to seek not only the development and deployment of the Golden Dome but also the resumption of stalled multilateral arms reduction talks[24] aimed at advancing strategic arms control and limiting nuclear weapons[25].

Japan’s Response to the Golden Dome Initiative

While the details of the Golden Dome initiative have not yet been officially disclosed, cross-agency discussions and coordination toward its concrete implementation have already begun under the leadership of the U.S. Department of Defense, involving relevant government agencies and defense commercial firms[26]. As it becomes a priority for the Trump administration, efforts to accelerate the development and deployment of key components of the Golden Dome—such as the initiative’s multi-purpose satellite constellations[27] and the Joint All-Domain Command & Control (JADC2) military network system—are expected to advance the early realization of the Golden Dome[28]. In this context, how should Japan, a key U.S. ally, respond?

・Strengthening Cooperation in Space

To protect the lives and property of its citizens from the growing airborne threats in East Asia, Japan should initiate discussions on developing an IAMD system in coordination with the United States, which is advancing the Golden Dome Initiative. Given that the core of the Golden Dome consists of detection and tracking sensors and interceptor systems deployed in space, this presents an opportunity for the reassessment of the interoperability of U.S.-Japan space assets in countering global airborne threats. Furthermore, cooperation between the U.S. Space Force—poised to play a central role in the Golden Dome—and the Japanese Self-Defense Forces should be strengthened[29].

・Evolution of Joint Development and Technological Cooperation

The Golden Dome Initiative aims to be realized in stages by the 2030s, necessitating the urgent adoption of Evolutionary Acquisition and Spiral Development (EA/SD)[30] for its phased deployment. In this context, Japan and the United States—longtime partners in co-developing missile defense systems[31] such as the SM-3 Block IIA—are currently collaborating on the development of a Glide Phase Interceptor (GPI) designed to engage hypersonic missiles before atmospheric reentry, as part of efforts to develop next-generation missile defense systems. Moving forward, Japan’s aerospace and defense industries could cooperatively contribute to the initiative by developing equipment and software for the Golden Dome[32]. The presidential directive on the Golden Dome explicitly emphasizes the need to strengthen collaboration with allies and partners across development, capability enhancement, and operations[33].

・International Cooperation in Defense Industry

Cooperation in the development of the Golden Dome—an integrated system of systems—is expected to foster collaboration among industry, academia, and government, including the Acquisition, Technology and Logistics Agency (ATLA), JAXA, and the private commercial sector. This could stimulate domestic technological innovation and strengthen Japan’s indigenous defense industrial base.
Given that NATO also regards IAMD as an urgent priority[34], and in light of the growing trend toward joint development and procurement of advanced dual-use technologies[35], opportunities for trilateral industrial collaboration on IAMD-related capabilities—among Japan, the US, and NATO should be explored.

In Closing

As airborne threats become increasingly diverse and complex globally, Japan must place greater emphasis on strengthening IAMD cooperation and coordination with partner countries, anchored by the Japan-U.S. alliance. For instance, Japan, the United States, and South Korea have established a mechanism for sharing early-warning alert data on North Korean ballistic missiles launches[i][36] and have conducted trilateral ballistic missile defense exercises[ii][37], suggesting that the foundation for multilateral IAMD cooperation is already taking shape.
Building upon current Japan-U.S. cooperation under the Golden Dome initiative, opportunities also exist to deepen collaboration with friendly partners such as the Philippines[38] and Taiwan[39], particularly in areas including threat monitoring and intelligence sharing related to airborne threats. Specifically, examples could include the multilateral sharing of sensor data such as satellite imagery and radar feeds related to IAMD, as well as joint military exercises within existing multilateral defense cooperation frameworks.
With the United States designating Golden Dome as a key policy priority, Japan—facing urgent needs to enhance its own IAMD capabilities—must clarify its strategic position on this plan[40], and articulate specific cooperative initiatives and a clear roadmap, and publicly express its commitment to meaningful cooperation.

(2025/05/19)