sentences:  However, in the fall of 1942 the German Navy changed tactics and reduced their submarine activity in the Caribbean region to concentrate its activity on the North Atlantic convoy route and the approaches to northwest Africa.With the withdrawal of submarines from the Caribbean region the Sixth Air Force concentrated its efforts as a striking force on its primary function of guarding against possible attacks on the Panama Canal.With the end of the war, most of the wartime Caribbean air bases used for antisubmarine patrols were returned to civil authorities in late 1945 or early 1946.