An instructional film that describes the strategic principles and actual practice of Coastal Command's system of convoy protection by antisubmarine patrols as it evolved during World War II. It depicts a wide variety of aircraft and weapon systems, ranging from Spitfires to Sunderlands to Hudsons and Liberators. The impact of surface detection radar (ASV) , as along with the effects of Leigh Light spotlights, convoy formations and patrol lines, is detailed in the war against Nazi Germany's Uboat blockade of the British Isles and key shipping lanes supporting the war in the North Atlantic and Mediterranean.

Original release date: 1944