IFF Mark II was the first operational identification friend or foe system, developed by the Royal Air Force just before World War II. The Mark I, its predecessor, amplified the signals of the British Chain Home radar systems, triggering a radar display blip. It required manual tuning, and operators could not always distinguish between an enemy aircraft and a friendly one with a maladjusted IFF. The Mark II, deployed at the end of the Battle of Britain in late 1940, fixed this problem with an automatic gain control and three automatic tuners that covered a wider selection of radars. The Mark II's frequencies were sufficient for the early war period, but by 1942 many more radars were in use, including incompatible ones based on the cavity magnetron. The IFF Mark III eliminated the multiple tuners and operated on a single frequency that could be used with any radar; it entered service in 1943 and quickly replaced the Mark II.

Read more: https://en.wikipedia.org/wiki/IFF_Mark_II

_______________________________ Today's selected anniversaries:

1551:

Sue Takafusa, a military leader for the Ōuchi clan in western Japan, led a coup against the daimyō, Ōuchi Yoshitaka, leading to the latter's forced suicide. https://en.wikipedia.org/wiki/Tainei-ji_incident

1882:

The Vulcan Street Plant, the first hydroelectric central station to serve a system of private and commercial customers in North America, went on line in Appleton, Wisconsin. https://en.wikipedia.org/wiki/Vulcan_Street_Plant

1939:

NBC broadcast the first televised American football game, between the Fordham Rams and the Waynesburg Yellow Jackets. https://en.wikipedia.org/wiki/1939_Waynesburg_vs._Fordham_football_game

2009:

A 7.6 MW earthquake struck off the southern coast of Sumatra, Indonesia (damage pictured), killing 1,115 and impacting an estimated 1.2 million people. https://en.wikipedia.org/wiki/2009_Sumatra_earthquakes

_____________________________ Wiktionary's word of the day:

Plutonian: 1. (Greek mythology, Roman mythology) Of or relating to Pluto, the Greek and Roman god of the underworld; demonic, infernal. 2. (by extension) Of, relating to, or having characteristics associated with the underworld; dark, gloomy; mournful. 3. (by extension, geology) Synonym of plutonic (“of or pertaining to rocks formed deep in the Earth's crust, rather than by volcanoes at the surface of the Earth”) 4. (by extension, geology, historical) Synonym of plutonic (“of, pertaining to, or supporting plutonism, the theory that the rocks of the Earth were formed in fire by volcanic activity, with a continuing gradual process of weathering and erosion, then deposited on the sea bed, re-formed into layers of sedimentary rock by heat and pressure, and raised again”) [...] 5. (astrology) Pertaining to the astrological influence of Pluto, formerly regarded as a planet. 6. (astronomy) Of or relating to the dwarf planet Pluto. https://en.wiktionary.org/wiki/Plutonian

___________________________ Wikiquote quote of the day:

Silence is an ocean. Speech is a river. When the ocean is searching for you, don't walk into the language-river. Listen to the ocean, and bring your talky business to an end Traditional words are just babbling in that presence, and babbling is a substitute for sight.   --Rumi https://en.wikiquote.org/wiki/Rumi