Secret Weapon: U.S. High-Frequency Direction Finding in the Battle of the Atlantic

The war against U-boats in the Atlantic was won in part by a high-frequency direction finder -- called Huff Duff or HF/DF for short -- that could pinpoint the location of radio transmitters. The story of HF/DF's development and operation in combat by the U.S. Navy is told here for the first time in revealing detail.