 Addison and Jones investigated the failure, and the Royal Aircraft Establishment discovered from the "X-Gerät" equipment in a shot down aircraft that it contained a filter set to 2000 Hz, whereas the jammers were set to 1500 Hz.Thereafter "X-Gerät" was successfully jammed by 80 Wing and the accuracy of German bombing declined until the Blitz ended in May 1941.On 23/24 April 1942, the "Luftwaffe" began a new campaign against the UK (the "Baedeker Blitz" ) with a sharp raid on Exeter, followed by a series of raids on other provincial cities.