Northrop Grumman reports it is to start production of RQ-4 Global Hawk unmanned aircraft systems for South Korea.

The four aircraft, together with two ground stations and supporting equipment, are being produced under a U.S. Foreign Military Sales program contract awarded in December of last year.

"It's clear that U.S. allies have seen the critical role Global Hawk plays for the U.S. Air Force around the world," said Mary Petryszyn, vice president, International, Northrop Grumman Aerospace Systems. "The system will be a vital link in the Republic of Korea's increasing leadership role in defending the peninsula."

The RQ-4 Global Hawk is a surveillance aircraft that uses high resolution synthetic aperture radar and long-range electro-optical/infrared sensors. It has a speed of about 375 miles, a range of 8,700 miles and a flight endurance time of about 28 hours. Both the U.S. Air Force and Navy employ the system.

Petryszyn called the sale of Global Hawks to the Republic of Korea "significant," since it's the first sale of the system to an Asia-Pacific ally under the FMS process.

The sale also follows decisions by Japan and Australia to procure long-endurance Northrop Grumman-made UAVs.

Deliveries of the UAV systems to Korea are expected to begin in 2018.