FILE PHOTO: An E-2D Hawkeye plane approaches to the U.S. aircraft carrier John C. Stennis during joint military exercise called Malabar, with the United States, Japan and India participating, off Japan's southernmost island of Okinawa, Japan June 15, 2016. REUTERS/Nobuhiro Kubo/File Photo

WASHINGTON (Reuters) - The U.S. State Department has approved the possible sale to Japan of up to nine E-2D Advanced Hawkeye Airborne Early Warning and Control aircraft for an estimated cost of $3.135 billion, the Pentagon said on Monday.

It said in a statement that Japan would use the aircraft to provide "situational awareness of air and naval activity in the Pacific region" and augment its existing E-2C Hawkeye fleet. A unit of Northrop Grumman Corp NOC.N will be the principal contractor.