World War II began with the shelling of the Westerplatte on 1 September 1939. Gauleiter Forster entered the High Commissioner's residence and ordered him to leave the City within two hours, and the Free City was formally incorporated into the newly formed "Reichsgau" of Danzig-West Prussia. Local SS and the police cooperated with the Germans with expelling Polish authorities from in and around the city. Polish civilian Post Office employees had received military training and were in possession of a cache of weaponsmostly pistols, three light machine guns, and some hand grenadesand were thus able to defend the Polish Post Office for fifteen hours. Upon their surrender, they were tried and executed. (The sentence was officially revoked by a German court as illegal in 1998.) The Polish military forces in the city held out until 7 September.