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Air traffic controllers from NORAD take over the civilian positions in the tower at Washington National Airport during the Skyshield II exercise. (National Archives and Records Administration)

“This Is Only a Test”

Fifty years ago, cold-war games halted all civilian air traffic—long before September 11 did the same.

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AT 8:53 A.M. ON SATURDAY, OCTOBER 14, 1961, Pacific Air Lines flight 715 from Sacramento rolled to its gate at Los Angeles International Airport and shut down its engines for 12 hours. At ticketing posts, a corps of temporary guides straightened their "World Way Blue" uniforms and accepted 50 cents for 20-minute tours of the new passenger terminal and the ramp. Inside the Pan Am 707 Jet Clipper Liberty Bell, stewardesses poured fresh Hawaiian fruit juice.

At every gate across the airport, airliners were receiving visitors but not passengers. United showed off its DC-8 and Boeing 720 jets, Convair 340, and Douglas DC-7A cargoliner. Bonanza opened its Fairchild F-27; Pacific Air Lines a Martin 4-0-4, and National Airlines a Lockheed Constellation. On the LAX ramp sat Western Airline’s tiny 1926 Douglas M-2 biplane.

LAX was only one of many airports to shut down. Nationwide, 50 civilian airports held open houses. But most passenger terminals just turned off the lights. Except for aircraft in Hawaii, the entire U.S. and Canadian commercial fleets and all civilian aircraft were grounded.

On that day, and on two others in the early 1960s, the airliners had to make way for waves of B-52 and B-47 bombers that were to cross from Canada into the United States and enter the continent from the coasts in a simulated Soviet nuclear attack. The three simulations, known as Sky Shield, were training exercises for the personnel, communications, and radar detection systems of North America. The plan was to make sure that the bombers were detected by radar and other early-warning systems, that interceptor and missile squadrons would be alerted and scrambled, and that the United States would remain able to strike back.

Operation Sky Shield II, which ran for 12 hours in October 1961, was the second time—and the longest—that U.S. civil air traffic had been grounded. The first was Sky Shield I, run on September 10, 1960, from 2 a.m. to 8 a.m. Eastern Daylight Time. The third and final time—until last September—was Sky Shield III: five and a half hours beginning at 3 p.m. EDT, September 2, 1962.

In 1951, 30 radars—the Pinetree Line—were constructed along the U.S.-Canada border. By 1954 Pinetree provided early warning of threats and control of friendly aircraft. In 1953, the first station of the more capable Distant Early Warning Line opened at Barter Island, Alaska. By 1957, nearly 60 DEW Line radars were installed 100 to 500 miles apart, within two degrees of the 69th parallel from Cape Lisburne, Alaska, to Cape Dyer, Baffin Island. The new Mid-Canada Line, which ran along the 55th parallel from British Columbia to the Labrador Sea, employed 90 unmanned stations consisting of an electronic "trip wire," an application of the Doppler effect, to detect aircraft.

Continental air defense seemed technically capable, but, untested by war, its true reliability was unclear. General Earle Partridge, commander-in-chief of North American Air Defense Command, hatched a plan for the first live test of the entire continental air defense force. Operation Sky Hawk was set for September 1959 but canceled days before, under the new NORAD commander, General Laurence S. Kuter. Would-be participants were advised to destroy all records. Representatives of the U.S. President, the Air Defense Commands of the United States and Canada, and the Canadian Chiefs of Staff Committee revisited the plan at Camp David, Maryland, on November 7, 1959, agreeing to the first (new and improved) joint exercise.

In October, the Ballistic Missile Early Warning System, which consisted of both detection and tracking radars, opened at Thule, Greenland. Detection radar was a fixed fan parabola, 165 feet high and 400 feet long—a football field on its side sending an invisible "V" 2,000 miles north toward the Soviet Union. The screen could withstand earthquakes and winds of 180 mph. Within the installation’s radomes were 55-ton tracking radars, which followed objects horizon to horizon.

If the ground-based radars, airborne radars, and sea-anchored radar platforms called Texas Towers worked as promised, NORAD expected advance warning of 12 to 20 minutes should an "air-breathing" attack occur along a 5,000-mile line looking north, from the Aleutian Islands to eastern Greenland. Ears and eyes reached out 3,000 miles toward the Red Menace, with the ability to detect a reflecting surface of one square foot—a basketball, or in practical terms, the nose of a B-47-type target. The ICONORAMA at Colorado Springs, the movie-screen-size display tracking all aerial activity in North America, displayed the DEW and Mid-Canada Line blips—up to 95 percent of targets, head-on, flying between 200 and 65,000 feet, within radar line of sight out to 150 miles. Low-altitude detection, mainly by the DEW Line, was projected to be valid from the surface to 10,000 feet.

Data from the DEW Line was fed to the four-story blocks on Strategic Air Command bases containing the 250-ton IBM computer called Whirlwind II, each of which had 49,000 vacuum tubes housed in a bunker that was reinforced to resist all but a direct nuclear hit. Controllers had previously used slide rules and paper charts, marking flight trajectories in grease on Plexiglas boards. The New York Defense Sector at McGuire Air Force Base in New Jersey was the first to get the Semi-Automatic Ground Environment (SAGE), which was enabled by Whirlwind. The Federal Aviation Agency (as it was known until 1967) hoped that simulations like Sky Shield, combining Air Defense Command with its own surveillance and air traffic control radars, would meld military command with FAA personnel through a program called SATIN (SAGE Air Traffic Integration). Under SAGE, the 600 daily civilian flights approaching the continent could now be checked against their authorized flight plans before they crossed the Air Defense Identification Zone, a buffer zone of airspace extending from the nation’s borders and shores. If the flight path was maintained, the aircraft was, by definition, peaceful. If it strayed, within a tolerance for weather and pilot error, identification was attempted by radio. If that failed, within minutes an interceptor would scramble for a visual check.

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