"The Defence of the Polish Post Office in Danzig was one of the first acts of World War II in Europe, as part of the September Campaign. On September 1, 1939, the Invasion of Poland was initiated by Germany when the Schleswig-Holstein battleship opened fire on the Polish-controlled harbor of Danzig, around 04:45-48 hours. Danzig paramilitaries and police, supported by Germany, immediately joined the offensive to take full control of the city, by capturing the Polish post office. Polish personnel defended the building for some 15 hours against assaults by the Heimwehr Danzig and special units of Danzig police. All but four of the defenders, who were able to escape from the building during the surrender, were sentenced to death by a German court martial as illegal combatants on October 5, 1939, and executed".