Long before radar networks and jet fighters, the RAF kept watch over the British Empire's furthest coastlines with flying boats, and this film traces that overlooked chapter of aviation history. Between the wars, elegant aircraft patrolled distant imperial waters, projecting British air power without a single runway in sight. When war came, the mission turned urgent: Short Sunderlands and PBY Catalinas flew punishing missions far out over open ocean, hunting enemy submarines and searching for downed aircrew whose survival depended on being spotted from the air. Archival footage and expert commentary reconstruct how these lumbering, boat-hulled aircraft operated from open water, what life was like for the crews who flew twelve-hour patrols over featureless sea, and why air-sea rescue became one of the RAF's most vital, least celebrated jobs. The film gives proper weight to a branch of the service usually left out of Spitfire-and-Hurricane narratives, showing how maritime aviation shaped Britain's reach both before and during the Second World War.