(Reel 1) Introduction states that film describes Coastal Command's anti-U-boat operations up to June 1944. "Although weapons and tactics and areas have changed since then, the strategic principles and organisation of command remain the same." Air Chief Marshal Sir Sholto Douglas sets scene by recalling his Command's other activities (meteorological reconnaissance, Air Sea Rescue, photo-reconnaissance by unarmed Spitfire, anti-shipping attacks by Beaufighter). Animation outlines the successive phases of the U-boat peril which confronted Britain: U-boats attempting to seal British ports, attempting blockade from the West, advance into US waters after 7th December 1941, crisis in Atlantic in March 1943. German production of U-boats in four main classes continued despite Allied air attacks (production scenes, launchings, iced-over U-boats, diving). In order to wear out U-boats' crews and batteries by forcing Germans to remain submerged, Coastal Command implemented theory of offensive anti-U-boat patrol enabling submarines to be caught on surface.

(Reel 2) Typical patrol, codenamed Percussion, over Bay of Biscay is described: patrols leave at half-hour intervals to ensure round-the-clock cover, Flying Fortresses flying by day and RAF Wellingtons and USN Liberators by night. Liberator of USN Fleet Air Wing 7 takes off (from St Eval) after crews have been briefed. Wellingtons equipped with Leigh Light (in use since 1942) stands parked on airfield before take-off; dramatised sequence shows crew members on night anti-submarine operation, with radar officer scanning ASV screen and navigator lowering and switching on Leigh Light prior to order to release depth charges. Organisation of Coastal Command is described: HQ at Northwood, 16 Group against surface shipping along North Sea enemy coast, 19 Group against U-boats in Bay of Biscay, 15 Group covering Western Approaches, 18 Group against enemy shipping off Norway and Iceland, 106 Group at Benson. Close collaboration between HQ (Leigh-Mallory at table) Air Ministry and Admiralty supports chain of command extending from HQ to Group to operational stations in Group, suggested by telephone, wireless and teleprinter working scenes. Aerial view of Plymouth introduces scenes at 19 Group's HQ: communications, RAF Cyphers Room, Operations Room with Admiral Sir Ralph Leatham, AOC Air Vice Marshal B E Baker and USN Fleet Air Wing Representative standing together, aircraft movements board with Mauritius Volunteer Reserve wireless telegrapher at receiver.

(Reel 3) [Reel uncatalogued, held only as 16mm mute duplicate negative.]

(Reel 4) Animation shows Coastal Command's strategic links with Eastern Air Command of the RCAF and the USN's Eastern Sea Frontier. Critical gap in Allied air coverage of Atlantic was filled in October 1943 when British landed in Azores and rapidly completed construction of airfield base protected by Portuguese Army. Air Vice Marshal G R Bromet as commander of Azores Area Combined HQ works with naval and air staff, including senior RN Commodore R B Holt. RAF Flying Fortresses and a Dakota of American Air Transport Command stand on the airfield. Map of Coastal Command's main bases and major convoy routes introduces factual history of one particular convoy from Gibraltar to the UK to show how coastal bases are used. Merchant vessels lie moored off Gibraltar (including freighter with severely damaged stern, and Greek and Dutch vessels), with escort comprising HMS Anthony, Queen Elizabeth Class battleship, HMS Colombo and HMS Active. Catalinas fly over convoy. Merchant skippers of convoy are briefed by RN and Coastal Command officers and are wished good luck by Vice-Admiral Commander-in-Chief Gibraltar. Convoy sets out at dawn, with Hudsons taking off to patrol and Sunderland (with RAAF crew) setting off from Mountbatten, Plymouth (past Dido Class cruiser). Animation traces routine patrols from Gibraltar, Azores and UK.

(Reel 4) Dramatised sequence of U-boat attack against ship and night blaze at sea suggests lurking enemy which Hudsons, Fortresses (signalling to convoy), Wellingtons, Liberators (from St Eval and Ballykelly) and Sunderlands (crew in launch at Castle Archdale) are hunting in their dovetailed pattern of patrols. Leigh-Mallory in Flight Operations Room follows progress of convoy, described over twelve day period as it comes under (diagrammatic) attack from Heinkel He 177s and Focke-Wulf 290s. Convoy arrives safely for loss of two aircraft and two damaged escort vessels, without a single U-boat attack on a merchant ship. Film closes with Churchill's voice: "I still rate highest among the dangers we are overcoming the U-boat attacks upon our shipping without which we cannot live or even receive the help which our Dominions and our grand generous American ally have sent us".

Instructional film describes strategic principles and actual practice of Coastal Command's system of convoy protection by anti-submarine patrols.

Notes

Technical: last reel has US leader marked "Coordinator of Information Photographic Representation Division 0076 OSS Reel 5 822ft". Reels were previously incorrectly numbered 1 to 5 owing to the inclusion as Reel 3 of part of the separate Crown Film Unit dramatised documentary COASTAL COMMAND (COI 426), now renumbered COI 426. The correct Reel 3 is now RMY 195/3, as indicated in the Summary.