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Project Mogul (sometimes referred to as Operation Mogul) was a top secret project by the US Army Air Forces involving microphones flown on high altitude balloons, whose primary purpose was long-distance detection of sound waves generated by Soviet atomic bomb tests. The project was carried out from 1947 until early 1949. The project was moderately successful, but was very expensive and was superseded by a network of seismic detectors and air sampling for fallout, which were cheaper, more reliable, and easier to deploy and operate.
Project Mogul was conceived by Dr. Maurice Ewing who had earlier researched the deep sound channel in the oceans and theorized that a similar sound channel existed in the upper atmosphere: a certain height where the air pressure and temperature result in minimal speed of sound, so that sound waves would propagate and stay in that channel due to refraction. The project involved arrays of balloons carrying disc microphones and radio transmitters to relay the signals to the ground. It was supervised by Dr. James Peoples, who was assisted by Dr. Albert P. Crary.
One of the requirements of the balloons was that they maintain a relatively constant altitude over a prolonged period of time. (See aerostat.) Thus instrumentation had to be developed to maintain such constant altitudes, such as pressure sensors controlling the release of ballast.
The early Mogul balloons consisted of large clusters of rubber meteorological balloons, however, these were quickly replaced by enormous balloons made of polyethylene plastic. These were more durable, leaked less helium, and also were better at maintaining a constant altitude than the early rubber balloons. Constant altitude control and polyethylene balloons were the two major innovations of Project Mogul.
Project Mogul was the forerunner of the Skyhook balloon program, which started in the late 1940s, as well as two other espionage programs involving overflights and photographic surveillance of the Soviet Union in the mid-1950s, Project Moby Dick and Project Genetrix. The spy balloon overflights raised storms of protest from the Soviets. The constant-altitude balloons also were used for scientific purposes such as cosmic ray experiments.
Echoes of Mogul's experimental infrasound detection of nuclear tests exist today in ground-based detectors, part of so-called Geophysical MASINT (Measurement And Signal INTelligence). In 2013, this world-wide network of sound detectors picked up the large explosion of the Chelyabinsk meteor in Russia (see Chelyabinsk article for details). The strength of the sound waves was used to estimate the size of the explosion.
Project Mogul and the Roswell Incident
In 1994-1995, in response to an official inquiry by New Mexico Congressman Steven Schiff, the Air Force published a report that advanced the theory that Mogul Flight #4, launched from Alamogordo, New Mexico, on June 4, 1947, was what crashed near Roswell, New Mexico, and formed the source of the debris that sparked the Roswell UFO Incident.
However, the alleged Flight #4 does not exist in Mogul's own records, said to have been cancelled because of cloudy weather, according to project scientist Albert Crary's diary. Similarly, the previously planned Flights #2 and #3 were also cancelled and thus absent from the records. Instead, the records show Flight #5 from the next day, June 5, 1947, as being the first actual Mogul flight in New Mexico. (flight summary table above right)
Several official histories of flight also indicate Flight #5, not #4, as the first such New Mexico Mogul flight.
- Project Genetrix and Soviet protests 
- Report on Project Mogul Synopsis of Balloon Research Findings by James McAndrew, 1st Lt, USAFR
- The Roswell Report: Fact versus Fiction in the New Mexico Desert.
- 1)Chronology: From the Cambridge Field Station to the Air Force Geophysics Laboratory 1945-1985, (AFGL, Hanscom AFB, Special Reports, No. 262, 6 Sept 1985), p. 3: “1947, 5 Jun, The first Army Air Forces research balloon launch was conducted at Holloman Air Force Base, New Mexico, by a New York University team working under contract for the Air Material Command. It featured a cluster of rubber balloons."; 2) Aeronautics and Astronautics: An American Chronology of Science and Technology in the Exploration of Space, 1915-1960 (NASA, 1961), 1945-1949, pp. 49-63: “1947, June 5: First AAF research balloon launch (a cluster of rubber balloons) at Holloman, by New York University team under contract with the Air Materiel Command.”; 3)U.S. Air Force: A Complete History, (The Air Force Historical Foundation, 2006), p. 300, “1947, 5 June, A New York University team under contract with the Air Materiel Command launches the Army Air Forces' first research balloon. The cluster of rubber spheres is released at Holloman, New Mexico.”
- Physics lecture video in which Prof. Richard A. Muller gives a detailed explanation of the science of Project Mogul (YouTube)
- Obituary of the man who launched the balloon http://www.nmt.edu/news/3704-charles-b-moore-1920-2010