Editing Metal detector (section)

=== Modern developments ===
The modern development of the metal detector began in the 1920s. [[Gerhard Fischer (inventor)|Gerhard Fischer]] had developed a system of radio direction-finding, which was to be used for accurate navigation. The system worked extremely well, but Fischer noticed there were anomalies in areas where the terrain contained ore-bearing rocks. He reasoned that if a radio beam could be distorted by metal, then it should be possible to design a machine which would detect metal using a search coil resonating at a radio frequency. In 1925 he applied for, and was granted, the first patent for an electronic metal detector. Although Gerhard Fischer was the first person granted a patent for an electronic metal detector, the first to apply was Shirl Herr, a businessman from Crawfordsville, Indiana. His application for a hand-held Hidden-Metal Detector was filed in February 1924, but not patented until July 1928. Herr assisted Italian leader [[Benito Mussolini]] in recovering items remaining from the [[Caligula|Emperor Caligula's]] galleys at the bottom of [[Lake Nemi]], Italy, in August 1929. Herr's invention was used by Admiral Richard Byrd's Second Antarctic Expedition in 1933, when it was used to locate objects left behind by earlier explorers. It was effective up to a depth of eight feet.<ref>
{{Cite book
 | first= Thomas C.
 | last= Poulter
 | title= Outline of the Scientific Accomplishments of the Byrd Antarctic Expedition II, 1933–1935
}}
</ref>
However, it was one [[Lieutenant]] [[Józef Kosacki|Józef Stanisław Kosacki]], a Polish officer attached to a unit stationed in [[St Andrews]], [[Fife]], Scotland, during the early years of [[World War II]], who refined the design into a practical [[Polish mine detector]].<ref>
{{Cite book
 | first= Tadeusz
 | last= Modelski
 | title= The Polish Contribution to The Ultimate Allied Victory in The Second World War
 | location= Worthing, England
 | year= 1986
 | page= 221
}}
</ref>
These units were still quite heavy, as they ran on vacuum tubes, and needed separate battery packs.

The design invented by Kosacki was used extensively during the [[Second Battle of El Alamein]] when 500 units were shipped to [[Bernard Montgomery, 1st Viscount Montgomery of Alamein|Field Marshal Montgomery]] to clear the minefields of the retreating Germans, and later used during the [[Allied invasion of Sicily]], the [[Allied invasion of Italy]] and the [[Invasion of Normandy]].<ref>
{{Cite book
 | first1= Mike
 | last1= Croll
 | first2= Leo
 | last2= Cooper
 | title= The History of Landmines
 | year= 1998
 | publisher= Pen & Sword Books
 | isbn= 978-0-85052-628-8
}}
</ref>

As the creation and refinement of the device was a wartime military research operation, the knowledge that Kosacki created the first practical metal detector was kept secret for over 50 years.