Northrop Grumman has publicly detailed, for the first time, how work is divided between the United States and Japan in the co-development of the Glide Phase Interceptor (GPI), a next-generation missile designed to defeat hypersonic threats.
At a media briefing in Tokyo on April 22, the U.S. defense contractor presented a schematic outlining the allocation of key components between the two nations, providing concrete substance to earlier statements that the program is structured as a “50-50” partnership.
While Japan’s Ministry of Defense had previously described the general framework of the U.S.-Japan workshare in Japanese, Northrop Grumman’s latest briefing offered a more detailed and granular breakdown.
The GPI is designed to intercept hypersonic glide vehicles (HGVs) traveling at speeds exceeding Mach 5 during their glide phase—an engagement window that has proven difficult for existing ballistic missile defense systems. The program was formally agreed upon at the August 2023 summit between then–Prime Minister Fumio Kishida and U.S. President Joe Biden, underscoring the growing urgency of countering advanced missile threats in the Indo-Pacific.
A Clearly Defined Workshare
According to Northrop Grumman’s presentation, the interceptor is a three-stage missile with clearly delineated responsibilities between the two countries.
The United States is responsible for the first-stage booster, the third-stage solid rocket motor, and key elements of the kill vehicle, including the aeroshell, avionics package, and seeker—components central to sensing, guidance, and terminal engagement.
Japan, for its part, is assigned the second-stage solid rocket motor and the third-stage attitude control system (ACS), both critical for flight stability and trajectory control. In addition, Japan contributes to the kill vehicle by developing the rocket motor, fin actuators, and fins, directly influencing terminal maneuverability.
The schematic presented at the briefing visually reinforced this division, highlighting a distribution in which U.S. contributions are concentrated in propulsion and sensor integration, while Japan plays a significant role in flight control and maneuver systems.
Depth of Japan’s Contribution
One of the key takeaways from the disclosure is the extent of Japan’s involvement. Rather than supplying isolated components, Japan contributes to critical elements of propulsion, attitude control, and terminal maneuvering.
This structure reflects a high degree of technical integration between the two nations, consistent with Northrop Grumman’s characterization of the program as a balanced workshare.
Industry and Alliance Integration
Troy Brashear, Vice President for International Space Business Development at Northrop Grumman, emphasized that the GPI program reflects broader cooperation across the missile defense kill chain.
“Northrop Grumman is involved in the full spectrum of missile defense— from understanding the threats to killing the attack vehicle and making the battle damage assessment,” Brashear said. “But what I would also like to highlight is the partnership and collaboration between the United States and Japan across each of these segments.”
He added that the program is designed to counter what he described as a “real” and “imminent” hypersonic threat, particularly for Japan given its geographic proximity to potential adversaries.
Brashear also pointed to the diagram shown during the briefing, noting that it illustrates a “50-50 content share” between the two countries across missile stages and the kill vehicle.
Program Status
Northrop Grumman’s GPI concept was selected in 2024, marking a key milestone in the program’s development.
Northrop’s GPI concept has three features: 1) acceleration by a three-stage rocket motor, 2) destruction of the target by a kill vehicle in the warhead section, and 3) launch from an Aegis destroyer’s vertical launch system (VLS), according to Japan’s Ministry of Defense.
In November 2024, the Ministry of Defense in Tokyo signed a contract with Mitsubishi Heavy Industries worth about 56 billion yen (around $350 million) for the design and manufacture of Japan’s assigned components, with delivery scheduled for March 2029.
The GPI is expected to be deployed on Japan Maritime Self-Defense Force (JMSDF) Aegis destroyers as well as the planned Aegis System Equipped Vessels (ASEVs). Japan aims to field the first ASEV by March 2028, followed by a second by March 2029.
A Next-Generation Interceptor
The GPI builds on earlier U.S.-Japan missile defense cooperation, most notably the SM-3 Block IIA, but represents a significant step forward in addressing hypersonic threats that challenge existing defense architectures.
As development progresses, the program is likely to serve as a key benchmark for future U.S.-Japan defense industrial cooperation, particularly in terms of technological integration and alliance interoperability. Whether the two countries can translate this balanced workshare into an operational capability against hypersonic threats will be a key question for regional security in the coming years.