FROM:  The Bomber Command Historical Society

100 Group were formed on November the 23rd 1943, with their headquarters at Radlett in Hertfordshire, although they soon relocated to Bylaugh Hall near Swanton Morley in Norfolk. Also known as "100 (Bomber Support) Group, they were the "clandestine" side of Bomber Command. Their trade was electronic warfare, radio countermeasures, radar jamming, and night-fighter activities. They flew a wide and varied assortment of aircraft, predominantly from airfields in East Anglia. From the fast twin-engined Mosquito to the four-engined "Heavies", 100 Group sent them all up, and by the end of the war had played a huge part in reducing the effectiveness of the Luftwaffe night-fighters and ground defences. although disbanded in December 1945 with the same Commander as it has started out with (Air Vice-Marshall Addison), it had played a large part in giving credibility to the new form of conflict - electronic warfare. 

FROM: The R.A.F. official history website

The creation No 100 Group within Bomber Command saw Mosquitoes employed electronic counter-measures (ECM) and 'spoof' sorties over Germany to deceive defending forces. Others joined the main bomber force and sought out German fighters whist the bombers attacked their targets. One little recorded mission of a small number of Mosquitoes was espionage. Operated by British Overseas Airways (one of the forerunners of British Airways), the aircraft were disarmed and modified to carry a 'passenger' in the bomb bay. In January 1943 they started a 'courier' run between Stockholm and Leuchars and flew a total of 520 flights before the service ended.