Operation Diver was the British codename for countermeasures against the V-1 flying bomb campaign launched by the German Luftwaffe in 1944 against London and other parts of Britain. Diver was the codename for the V-1, against which the defence consisted of anti-aircraft guns, barrage balloons and fighter aircraft. The British Double-Cross System used Double agents to plant false information about the accuracy of the V-1 bombardment. Anti-aircraft guns proved the most effective form of defence in the later stages of the campaign, with the aid of radar-based technology and the proximity fuse. The V-1 campaign from ground launch sites ended by the middle of 1944 with the Allied occupation of the launch sites.