Big Fence

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.

Answering call sign "Big Fence", the central plotting room inside the castle triangulated information from seven direction finding installations, including the Castel headquarters.

[2] 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.

Please accept my personal thanks for your superior work with the 15th.Please convey our hope that if the fortunes of war again bring us together, we may have the privilege of calling "Big Fence" in our hour of need

Castel Del Monte made an excellent landmark that could be seen for considerable distances during VHF site selection reconnaissance.
15th AF Navigational Aid Facilities Map
“YANK, The Army Weekly”, March 23, 1944, p. 20
Sicily Stars and Stripes April 25, 1944, p.3
Mediterranean Naples Stars and Stripes, April 19, 1944, p.5