September 1939
Day by day chronology

FRIDAY, 1 SEPTEMBER 1939
Germany: Before dawn, Germany begins attacking western Poland, At 4:40am Luftwaffe aircraft attack Wieluń as German troops begin crossing the border. At 4:45am German pre-dreadnought battleship Schleswig-Holstein openes fire on the Polish military transit depot at Westerplatte in Danzig on the Baltic Sea. World War II in Europe begins.

SUNDAY, 3 SEPTEMBER 1939
UK/France: United Kingdom and France declare war on Germany after the invasion of Poland and few skirmishes occur on the German-French border.

TUESDAY, 12 SEPTEMBER 1939
(JAAF) Reconnaissance flight over Tamsagbulag and Buir Nur observes 16 twin engined aircraft and 68 fighters on the ground.

FRIDAY, 15 SEPTEMBER 1939
JAAF: Ki-27s from 59th Sentai flew the unit's only combat mission with the 2nd Chutai claiming eleven aerial victories and the 1st Chutai lost five pilots.

IJA/Soviet: The Soviet-Mongolian and Japanese-Manchukuo forces agreed to a cease fire that would go into effect the next day and will end the Battle of Khalkhin Gol (Nomonhan Incident).

SATURDAY, 16 SEPTEMBER 1939
USSR/Mongolia/IJA/Manchuria: At 1:10pm local time, the Soviet-Mongolian and Japanese-Manchukuo forces agreed to a cease fire goes into effect ending Battle of Khalkhin Gol (Nomonhan Incident).

SUNDAY, 17 SEPTEMBER 1939
USSR: Soviet Union invades eastern Poland in accordance with the "secret additional protocols" of the Molotov–Ribbentrop Pact.