"Radar and Electronic Warfare 1939-1945" Aircraft Navigation and Guidance: MPs visiting No 554 Anti Aircraft Battery near Harwich watching a demonstration of a searchlight with radar equipment known as ELSIE - 90 cm Searchlight Control Radar (SLC) No 2 Mk VI - which entered service in 1942 and was of immense assistance to anti-aircraft when used against the flying bomb attacks of 1944.