The Aegis system brings together powerful radar and missiles to locate and intercept several incoming missiles or attack aircraft simultaneously. Japanese vessels equipped with the system currently employ Lockheed Martin's SPY-1 radar. The U.S. Navy plans to upgrade its ships with Raytheon's SPY-6, which can detect missiles more than 1,000 kilometers away, or more than twice as far as the SPY-1.

The U.S. and Japan now aim to develop an even longer-range system that is also more compact, letting ships stationed in the Sea watch for missiles across all of the Korean Peninsula and part of eastern China.

Washington apparently broached the topic of collaborating on this next-generation system at high-level military talks in June. It hopes to incorporate technologies from companies such as Mitsubishi Electric that use gallium nitride chips, which make radar systems much more powerful at little additional energy cost. While American contractors have similar technology, Japan is thought to be the leader in the field.

The countries are expected to agree on the joint project as early as this year. Studies would come first, preparing for mass production five or 10 years down the road. Japan plans to begin budgeting research expenses for the project as early as in fiscal 2019.

Aegis is largely a collection of American technologies. That Japan will be involved in such a key piece of the system as radar and will contribute chips, the locus of its technological power, signifies a deepening bilateral cooperation on security.

With the finished system likely be exported to other American allies, Tokyo hopes the undertaking will benefit the Japanese contractors involved.