Context : The Gleiwitz incident (German: Überfall auf den Sender Gleiwitz; Polish: Prowokacja gliwicka) was a false flag operation by Nazi forces posing as Poles on 31 August 1939, against the German radio station Sender Gleiwitz in Gleiwitz, Upper Silesia, Germany (since 1945: Gliwice, Poland) on the eve of World War II in Europe. 
Answer : 31 August 1939
On what date did Gleiwitz incident occur?