Two Predator drones were tested on Kauai this summer as ballistic missile trackers as the U.S. Missile Defense Agency seeks to expand its launch detection capabilities without adding costly and sometimes diplomatically unacceptable land-based radars abroad.

General Atomics Aeronautical Systems said Tuesday that its multimission Predator B/MQ-9 Reaper drones were used to detect and track a ballistic missile target as part of an ongoing program with the Missile Defense Agency.

The tests were conducted in late June during Pacific Dragon exercises at the Pacific Missile Range Facility on Kauai. Pacific Dragon was a trilateral ballistic missile defense tracking event involving the Navy, the Japan Maritime Self-Defense Force and the Republic of Korea Navy.

This year’s drills included a coordinated live ballistic target tracking event in which each nation’s Aegis ballistic missile defense system capabilities were tested and improved with participants sharing tactical data link information, according to the Navy.

The Korea Times said it was the first such drills involving the three countries. It drew an angry reaction from North Korea, which vowed to add to its nuclear arsenal. The Predator B drones also exercised with Navy ships.

“The test provided valuable data in our ongoing effort to develop an effective airborne missile defense capability,” Linden Blue, CEO of General Atomics Aeronautical Systems, said in a news release.

The Predators used Raytheon electro-optical infrared targeting system turrets to track the simulated missiles. The Missile Defense Agency said it is developing and testing new technologies to intercept and destroy ballistic missiles during the ascent phase of flight.