The end of the Second World War saw massive technology transfers from Europe’s two leading military and economic powers, Nazi Germany and Great Britain, to the United States to bolster its economy and defence sector in preparation for the coming Cold War. While the latter came as a result of technology sharing agreements, which were frequently considered one sided in their implementation and were imposed when Britain was in dire financial straits, the former came as a result of mass defections by German scientists to the U.S. – with many having been actively sought out and recruited by U.S. intelligence under Operation Paperclip. While some of the better known benefits to the U.S. of the technology transfers affected its military aviation and several of its missile programs, a less well known project which was pursued by the newly formed Central Intelligence Agency (CIA) was to develop an air-driven siren which could be attached to small aircraft for psychological warfare operations.
The inspiration for the CIA’s new weapon, designed to cause terror in those who heard it with a very unique and overwhelming sound, was the German ‘Jericho Horn,’ as it was known in the U.S., attached to the Luftwaffe’s Ju-87 Stuka dive bombers. The CIA had focused heavily on psychological warfare operations, or ’psy-ops,’ in the Cold War’s early years, from mimicking ‘vampires’ and employing other often phantasmic means in the Philippines to undermine support for Hukabulahap insurgents under renowned officer Edward Lansdale to spreading anti communist sentiments in southern Vietnam. An unknown CIA officer made a handwritten request for “a siren or screamer type noisemaker for psychological warfare” in May 1958 for further operations. The requirement reportedly originated with the CIA’s Far East Division, with the program to acquire the device referred to as the “Screamer Project.”
The CIA reportedly wanted the new siren to be integrated onto the P-51 Mustang, an obsolete propeller driven fighter of which the U.S. had hundreds in storage as surplus, and to be operable while the aircraft was flying at low speeds between 280 and 300 miles per hour and at low altitudes. While the agency would later go on to field its own specialised military aircraft such as the A-12 spy plane the following decade, in the 1950s it still relied heavily on surplus aircraft from the Second World War for operations against a number of countries from Guatemala to Indonesia and North Korea. The CIA notably struggled to develop the ‘terror siren’ needed, and would instead seek to find a German Ju-87 for study. Acquiring the siren would prove far more difficult than anticipated, however, as not only had the Air Force misplaced the one Stuka aircraft it had captured, but the Smithsonian Institution and the Museum of Science and Industry in Chicago were both checked in vein with neither holding the much sought after terror weapon.
The CIA would ultimately give up on finding a complete variant of the Jericho Horn, and instead sought out Henning Von Girke, who had been recruited to the U.S. under Operation Paperclip and had designed the original terror horn. He was asked to provide design notes and technical details on the siren. The agency would commission four prototype Jericho Horns in late 1958 based on this information, with the name of the firm that built them still being classified, and by the end of October 1958 the contractor had begun putting them through testing in a laboratory environment. Tests showed that the device could generate a sound 150 decibels loud – with 130 to 140 decibels typically considered the threshold for pain. The CIA reported that the siren’s output could be increased to between 170 to 180 decibels “by electronic means,” and work would continue into 1959 with the first test flights carried out in January that year.
The Beechcraft AT-11 was used to test the first Jericho Horns, and when integrated there was an adjustable iris for the whistle that would alter the air flow and change the sound output. The new siren failed in testing however, producing only 108 decibels at maximum which left it considerably weaker than the estimated power of its German predecessor. A CIA report on the flight tests stated regarding its underperformance: “In the present state this whistle can not be considered as a harassment item. It does however attract attention… Upon hearing the whistle for the first time, and completely unaware that any such device was being tested, a charter pilot, who flew the undersigned to the test site, was of the opinion that either the oil or fuel pump of the test aircraft was failing. He expressed concern for fear the test aircraft might crash due to motor failure. Although this unbiased witness was concerned about the noise, he was not frightened to any degree.”
The CIA would begin another set of flight tests for the Jericho Horn in March 1958 using the smaller Cessna Model 180 aircraft, with two different modified variants of the siren used. Both failed, with a CIA report dated March 31 stating: “At present the ‘Jericho Horn’ does not satisfy this requirement [for a psychological warfare device], and it is doubtful that continued effort will achieve this end.” A report from the engineering division stated regarding the terror program: “If this whistle cannot serve any useful purpose as a psychological identification device, it is our recommendation that this project be dropped.” The project was ultimately cancelled, although the U.S. would seek to develop other kinds of terror weapons including the ’Screeming Meemie’ in following decade, although this too was considered a failure. While the CIA never managed to acquire the Nazi terror weapon it had sought to use in East Asia, sound based terror tactics were common during the Cold War. The U.S. Air Force would use sonic booms from supersonic aircraft once these became more widely available as a terror weapon against targets such as Libya, Cuba and North Korea, and more recently invested in development of propaganda devices which could be dropped on enemy territory to play various recorded messages among multiple other propaganda and psychological programs that utilised aircraft.