Battle of Ushant: intelligence and radar

The German force sailed while the Allies were still establishing the Normandy lodgement, with two Narvik-class destroyers, the captured Dutch destroyer ZH1, and the torpedo boat T24. British intelligence combined Enigma material with the radio-listening system nicknamed Headache. The volume of German radio traffic could reveal enemy activity, although harbour manoeuvring sometimes created a noisy or misleading picture. Plymouth command used that information to coach the 10th Flotilla into a favourable position. Tartar's Type 276 radar then found the German force at a bearing of 241 degrees and a range of ten miles. Closing farther increased the chance of a decisive surprise, but also risked losing it before the British opened fire. German radar provided some warning, and moonlight finally revealed how close the Allied destroyers had come before the Germans turned away and launched torpedoes.