Big Fence was a secret navigational aid for US Army Air Force sorties from North Africa and Italy during World War II, ultimately located at the Castel del Monte in Apulia. It was operated by the 6649th Navigational Aids Squadron of the 341st Signal Company, XV Fighter Command, 15th Army Air Force."6649th Navigational Aids Squadron", 341st Signal Company, XV Fighter Command, The Fifteenth Air Force
The 6649th supported missions critically reliant on fixing the position of aircraft. Answering call sign "Big Fence", the central plotting room inside the castle triangulated information from seven direction finding installations, including the Castel headquarters.
From September 1943 until cessation of hostilities, the squadron received an estimated 16,000 calls for assistance from lost, damaged, and air-sea rescue craft. George Loving, Woodbine Red Leader: A P-51 Mustang Ace in the Mediterranean Theater, , 2007, p. 135 Kevin A. Mahoney, ”Fifteenth Air Force against the Axis: Combat Missions over Europe during World War II”, , 2013, p. 265 Kevin A. Mahoney, "Bombing Europe: The Illustrated Exploits of the Fifteenth Air Force", , 2015, p.38 Tom Ivie, Paul Ludwig, “Spitfires & Yellow Tail Mustangs: The U.S. 52nd Fighter Group in WWII”, , 2013, p. 229James M. Doyle, ”Flying Through Time”, , 2005, p. 206 Thomas Follis, “He Wore a Pair of Silver Wings”, , 2004, p. 187 Albert E. Conder, "Air Force Gunners", , 1994, p.122 Bill Disbrow, "On the Edge", , 2005, p.131 Brandon Sanders, "Heroes to Remember", , 2000, p.166 Sam Schneider, Byron L. Kennedy III, "This is How it was: 485th Bomb Group (Heavy) unit history", , 2000, p.124 Louis Falstien, "Face of a Hero", 1950, p.209 Ron White, "Headlong into Fury", , 2016, p.??? Charles E. Francis, "The Tuskegee Airmen: The Men who Changed a Nation", , 1997, p.166 Martin Caidin, "Fork-tailed Devil: The P-38", , 2001, p.247 William E. Knight, "Letters to the Twenty-Second Century, , 2001, p.108 John W. Walcott, "One Fighter Pilot’S War, , 2015, p.??? Gerard Paloque, "12th & 15th Air Forces", , 2011, p.??? Erik Dyreborg, "The Young Ones: American Airmen of WWII", , 2003, p.7 Sgt. August Loeb, YANK Staff Correspondent , March 23, 1944, p. 20
Being a VHF system, Big Fence was particularly valuable to fighters, which only had VHF radios. The bombardment groups could often rely on other navigational aids that were at their disposal, but only VHF remained effective in bad weather.
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