World War II in Europe began on Friday, 1 September 1939, when German forces invaded Poland. In preparation, 5./186 had been moved to Brüsterort, near Königsberg on 22 August. In the early morning hours of 1 September, 5./186 flew its first combat missions, providing fighter protection for 4./186 attacking the naval base of the Polish Navy at Hel and for the old German battleship "Schleswig-Holstein" bombarding the Polish military transit depot at Westerplatte in the Free City of Danzig on the Baltic Sea. The next, II./186 flew further bomber escort missions and was withdrawn from this theater on 6 September, relocating to Hage, East Frisia.