General Mark W. Clark, commander of the U.S.-Korean-allied coalition forces, and his staff, needed to know details of the enemy's strength, disposition and movements.

The Sabres were operated by the Japanese 501st Tactical Reconnaissance Squadron at Iruma Air Base where they remained in service until 25 March 1977.

The squadron also had a flight of seven specialized RT-33As equipped with sniffer gate valves and filters installed in the nose cone of the tips.

Initially sent to USAFE in 1955 to the 7407th Support Squadron in West Germany, they flew a number of successful missions over non-friendly territory in Eastern Europe.

The (Nationalist) Republic of China Air Force often passed the information gained by these reconnaissance flights along to US intelligence agencies.

The mission profile was briefed to fly north from Chitose and along the eastern side of the island of Sakhalin far enough seaward and at an altitude of 100 feet to avoid radar detection.

This profile was to continue to a point abreast the northern portion of the island where the tip tanks would be jettisoned and a climb initiated to the maximum obtainable altitude.

Somewhere in the climb a 180 degree turn would be started in order to arrive over the northern tip of the island headed south at an altitude of about 55,000 feet.

Another flight on 11 December used three RB-57s was approved in which the aircraft entered Soviet airspace simultaneously from three different locations near Vladivostok and overflew three different targets.

Contrary to Air Force hopes, the bombers were picked up on Soviet radar, and MiG-17s scrambled to intercept them; but the Americans were out of reach.

In the exposed film returned to the intelligence community, the fighters were clearly visible, pirouetting in the thin air beneath the bombers.

The resulting protest on 14 December left no doubt about the capabilities of Soviet air defenses to detect and identify aircraft: Four days after the Soviet note was delivered, an exasperated president met with United States Secretary of State John Foster Dulles to consider the embarrassing situation and decide on a course of action.

Instead, he instructed Colonel Andrew Goodpaster to relay an order to Secretary of Defense Charles Wilson, JCS chairman Gen. Nathan Twining, and Central Intelligence Agency director Allen Dulles: "Effective immediately, there are to be no flights by U.S. [military] reconnaissance aircraft over Iron Curtain countries."