April 1942 - ITS
Source: https://www.its.bldrdoc.gov/this-month-in-its-history/april-1942
Archived: 2026-04-23 17:36
April 1942 - ITS
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December 1964
December 1941
December 1918
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September 1970
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August 1958
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August 1912
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April 1942
April 1939
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February 2012
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January 1943
January 1909
Institute for Telecommunication Sciences
/ April 1942
In April of 1942, shortly after the U.S. entry into World War II, the Interdepartmental Radio Propagation Laboratory (IRPL) published its first ionospheric predictions. These predictions on the height and state of the ionospheric layer of the Earth’s atmosphere were used to determine which frequencies and paths would be most effective for radio communication. The ionosphere is made up of shifting plasma that reflects radio waves; it is necessary for radio communication in most situations. Knowing the height and state of the atmospheric layer allows more distant communication with reduced interference. IRPL had been sounding the ionosphere with radio waves and reporting their findings since 1939. By 1942, they could recognize patterns in the data that allowed them to predict the changing state of the atmospheric layer. Since the predictions were used heavily by the military to communicate with troops in the field, the published predictions remained top secret until the end of the war. Publishing ionospheric predictions was one of the most important missions undertaken by IRPL and its successor agencies for many years. ITS no longer publishes ionospheric predictions, but continues to improve telecommunication for everyone by studying the propagation of radio waves and developing new prediction algorithms.
Skip to main content
↑ Back to top
The .gov means it’s official.
Federal government websites often end in .gov or .mil. Before sharing sensitive information, make sure you’re on a federal government site.
The site is secure.
The
https://
ensures that you are connecting to the official website and that any information you provide is encrypted and transmitted securely.
ITS Home
This Month In ITS History
December 1964
December 1941
December 1918
December 1901
November 1965
November 1920
November 1918
October 1957
October 1997
October 1925
September 1970
September 1962
September 1954
September 1952
August 1958
August 1957
August 1912
July 1968
July 1957
July 1907
June 1961
June 1950
June 1910
May 1965
May 1946
May 1937
April 1950
April 1942
April 1939
March 1978
March 1976
March 1915
March 1901
February 2012
February 1927
February 1921
January 1958
January 1949
January 1943
January 1909
Institute for Telecommunication Sciences
/ April 1942
In April of 1942, shortly after the U.S. entry into World War II, the Interdepartmental Radio Propagation Laboratory (IRPL) published its first ionospheric predictions. These predictions on the height and state of the ionospheric layer of the Earth’s atmosphere were used to determine which frequencies and paths would be most effective for radio communication. The ionosphere is made up of shifting plasma that reflects radio waves; it is necessary for radio communication in most situations. Knowing the height and state of the atmospheric layer allows more distant communication with reduced interference. IRPL had been sounding the ionosphere with radio waves and reporting their findings since 1939. By 1942, they could recognize patterns in the data that allowed them to predict the changing state of the atmospheric layer. Since the predictions were used heavily by the military to communicate with troops in the field, the published predictions remained top secret until the end of the war. Publishing ionospheric predictions was one of the most important missions undertaken by IRPL and its successor agencies for many years. ITS no longer publishes ionospheric predictions, but continues to improve telecommunication for everyone by studying the propagation of radio waves and developing new prediction algorithms.