These Are the Planes the U.S. and Japan Use to Check on North Korea's Nuke Tests

The United States and Japan both sent

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jets near North Korea after Pyongyang's latest nuclear weapons test. The U.S. Air Force WC-135 "Constant Phoenix" and Japan Air Self Defense Force T-4 are planes designed to measure radiation released by a nuclear incident.

The U.S. Air Force sent a WC-135 "sniffer" plane from Offutt Air Force Base, Nebraska to Kadena Air Base on the island of Okinawa, and then on to the Korean peninsula. The WC-135 is a military version of the old Boeing 707 modified to collect radioactive particles from the atmosphere. The jet uses external flow devices to collect airborne particulate on filter paper and can analyze samples on board to detect radioactivity. The plane can also collect atmospheric samples in holding spheres for analysis on the ground.

The aircraft, tail number 62-3582, is one of two WC-135s left in the Air Force's inventory. In 2016 a WC-135 was harassed in international airspace by two Chinese Su-30 fighter jets, with one of the fighters flying inverted, "Top Gun" style, above the American plane.