Freya was first successfully used on December 18, 1939 when two stations detected an approaching daytime raid on Wilhelmshaven by 22 RAF Vickers Wellington bombers at a range of 113 km and guided fighter planes toward them via radio. Only half of the Wellingtons returned to Britain undamaged, but the German fighters only reached the bomber after they had made their bombing run on ships in harbour. The performance of Freya left the "Luftwaffe" so impressed that, by the Spring of 1940, eleven "Freya" stations were installed to guard Germany's western border. After the invasion of France in 1940, additional "Freya" stations were built along the Atlantic coast. When Britain started its bombing raids, Hermann Göring ordered Colonel (later General) Josef Kammhuber to install an efficient air defence. This led to the so-called Kammhuber Line into which more "Freya" stations were incorporated. In the later course of the war, "Freya" devices turned out to be vulnerable to chaff, along with other countermeasures, which meant they could still be used for early warning, but no longer for guiding fighter planes. British bombing raids could also be organized such that the Kammhuber Line could be overwhelmed in massed raids.