In mid-morning a Coastal Command Catalina reconnaissance aircraft from 209 Squadron RAF, which had flown over the Atlantic from its base on Lough Erne in Northern Ireland across the Donegal Corridor, a small corridor secretly provided by the Irish government,[8] piloted by British Flying Officer Dennis Briggs[9] and co-piloted by US Navy observer Ensign Leonard B. Smith, USNR,[10] Smith was at the controls when he spotted Bismarck (via a trailing oil slick from the ship's damaged fuel tank) and reported her position to the Admiralty. From then on, the German ship's position was known to the British, although the enemy would have to be slowed significantly if heavy units hoped to engage outside the range of German land-based aircraft. All British hopes were now pinned on Force H, whose main units were the aircraft carrier HMS Ark Royal, the battlecruiser HMS Renown and the light cruiser HMS Sheffield.