Stalin Moves On Poland; HMS Courageous Sunk

SUN 17 SEP 1939
USSR, its western border secure after its 23 August 1939 ceasefire with the Japanese along the Manchukuo-Mongolia frontier, invades eastern Poland.

British use of Home Fleet aircraft carriers to hunt German submarines, begun on 3 September, ends after U-29 torpedoes and sinks HMS Courageous southwest of the British Isles, 50°10'N, 14°45'W. Courageous is the first capital ship lost by any of the combatants. "A wonderful success," the German U-boat High Command War Diary exults, "and confirmation of the fact that the English defense forces are not as effective as they advertise themselves to be."

U.S. freighter Black Condor is detained by British authorities (see 24 September).