Following several German-staged incidents, such as the Gleiwitz incident, part of Operation Himmler, which German propaganda used as a pretext to claim that German forces were acting in self-defence, one of the first acts of war took place on 1 September 1939. At 04:45, the old German pre-dreadnought battleship "Schleswig-Holstein" opened fire on the Polish military transit depot at Westerplatte, in the Free City of Danzig, on the Baltic Sea. However, in many places, German units crossed the Polish border even before that time. Around then, the Luftwaffe attacked a number of military and civilian targets, including Wieluń, the first large-scale city bombing of the war. At 08:00, German troops, still without a formal declaration of war issued, attacked near the Polish village of Mokra. The Battle of the Border had begun. Later that day, the Germans attacked Poland's western, southern and northern borders, and German aircraft began raids on Polish cities. The main axis of attack led eastwards from Germany through the western Polish border. Supporting attacks came from East Prussia, in the north, and a joint German-Slovak tertiary attack by units (Field Army "Bernolák") from the German-allied Slovak Republic, in the south. All three assaults converged on the Polish capital, Warsaw.