Only a decade earlier, Japanese aircraft had devastated Pearl Harbor, Hawaii, thus pulling the United States into World War II. Later, members of the Japanese attack force admitted that they had easily navigated to their target by simply homing in on the AM radio signal of Honolulu station KGMB. American military leaders and civil defense planners would not soon forget such a modus operandi, and so they sought to develop a way to keep local broadcast communication flowing without providing a beacon for an enemy.

     Soviet Russia's 1949 acquisition of nuclear weaponry reminded nervous U.S. officials that bombers poised to deliver nuclear warheads could adroitly locate any of the several thousand American communities that had an AM radio outlet. On any given day or night in the New York metropolitan area, for example, each Russian flyer in the attacking squadron would have his choice of any one of over a dozen strong, standard broadcast stations. And to make matters worse, maps that ordinary folk, as well as spies, could buy from the federal government for a couple of dollars pinpointed the exact whereabouts of every significant AM transmitter tower.

     In 1951 President Harry Truman approved a plan to con­ trol all domestic radio waves so that navigators in enemy aircraft could not be aided by listening to an American broadcast station. The plan for control of electromagnetic radiation, which was simplified into the acronym "CONELRAD," was in practice a complex scheme of transmitter sign-offs and sign­ ons, power reductions, and frequency shifts designed to confound hostile bomber crews. It had the potential to confuse loyal Americans, too.

     A civil defense pamphlet printed shortly after CONEL­ RAD's implementation explained that "at the first indication of enemy bombers approaching the United States, [the Commanding Officer of the Air Division Defense or higher military authority will instruct] all television and FM radio stations to go off the air." In the days before portable, battery-powered TVs or FM personal or automobile radios, no one considered either service a reliable means of conveying emergency information. Typically, television and FM stations received their cue to sign off through a silence-sensor device that detected the sudden absence of key AM outlets, which had also been ordered to be quiet. In daisy-chain fashion, all television, FM, and AM stations would go silent. Along with the TV and FM facilities, many of these AM stations were required to stay dark in order to make way for certain designated CONELRAD AM stations that, during the brief shutdown, had quickly switched their transmitter frequency to either 640 or 1240 kilohertz (whichever was closest to each particular station's regular Federal Communications Commission (FCC)-assigned dial position) and then returned to the air with less than normal output power. Understandably, antenna systems customized for, say, 1600 kilohertz, suffered efficiency loss when coupled to a jury-rigged 1240-kilohertz transmitter. Officials admitted that "the changeover to CONELRAD [frequency and power level] takes a few minutes" and suggested that the understandably anxious public "not be alarmed by the radio silence in the meanwhile."

     Once the participating CONELRAD stations resumed broadcasting on their new (640-kilohertz or 1240-kilohertz) wavelength, they were all required to air the same emergency programming instructing the citizenry what to do next. During this information transmission, the CONELRAD outlets would sequentially shut down momentarily. The idea was to have, at any given time during the crisis, ample operating CONELRAD stations to reach the public while making normal radio station frequency, city-of-origin guides, and transmitter tower maps completely useless from an air-navigational standpoint.

     In theory, attempting to decipher the true identity of a CONELRAD station would be like trying to identify which person, in an auditorium filled with whisperers, was intermittently whispering. In practice, though, not all of these elaborate cloaked CONELRAD facilities were effective conduits for vital communication. This was especially true at 1240 kilohertz, to which many of the participating stations were switched. In CONELRAD test runs, suburbanites near New Brunswick, New Jersey, tuning to the I 240 spot occupied by local WCTC and not-too-distant WNEW (now WBBR) New York heard little there but unintelligible crosstalk interference. The 640-kilohertz CONELRAD setup was the better bet. On that less crowded lower dial position, the result included noticeable station overlapping and some heterodyne whistling, but it delivered readable signals to much of the country.

     A young broadcast buff, Donald Browne, recalled rushing home in late April of 1961 from his Bridgeport, Connecticut, high school to catch a CONELRAD dress rehearsal. He described this final CONELRAD system-wide test as sounding "real spooky," like something from The Twilight Zone television show. Browne noted that "several primary stations could be heard simultaneously on 640, all with the same program, each slightly delayed or out of phase with the others, like one weird echo effect ... and probably scaring more listeners than they informed."

     Most Cold War-era radio audiences took CONELRAD quite seriously. The government asked broadcasters to tout the warning system by ubiquitously airing public service announcements capped with a tiny jingle that went, "Six-forty, twelve-forty ... Con-el-rad." Then people were urged to "mark those numbers on [their] radio set, now!" Starting in 1953, though, every AM radio sold in America was required to have a civil defense logo triangle factory-printed on its dial at 640 and at 1240 kilohertz.

     In addition, CONELRAD regulations touched the amateur or "ham" radio community. As with commercial broadcast outlets, amateur stations were required to cease transmitting at the first sign of a CONELRAD activation. The consumer electronics maker Heathkit offered an inexpensive automatic alarm unit that would ring a bell and immediately cut off one's ham transmitter if any local broadcast station being monitored suddenly left the air. CONELRAD architects could take no chances with some unwitting 25-watt radio hobbyist who might innocently mention his backyard antenna's whereabouts during an atomic enemy sortie. Hams as well as staff at non­ participating CONELRAD radio and TV stations knew to listen closely to the official 640/1240 facilities for the "Radio All Clear." Initiated by the Air Defense Commander (or higher military official), this relief meant that the CONELRAD emergency test had ended and heralded the resumption of normal transmissions over regular AM, FM, TV, amateur, and other FCC-licensed frequencies.

     By the early 1960s, Soviet missiles, including those they briefly positioned in Cuba, made up a nuclear weapon delivery system far more sophisticated than an airplane navigated via some unsuspecting pop music radio station. Therefore, in 1963 CONELRAD was scrapped as obsolete. Its cumbersome 640/ 1240 frequency shifting, power reducing, and on/off sequencing went the way of the wind, but positive aspects of CONEL­ RAD's warning scheme (such as employing a series of primary, participating stations to reach the public) were revamped into the Emergency Broadcast System, which stayed in effect through 1996, when it, in turn, was superseded by the Emergency Alert System.