The Battle of Westerplatte was the first battle of the German invasion of Poland, marking the start of World War II in Europe. It occurred on the Westerplatte peninsula in the harbour of the Free City of Danzig (now Gdańsk, Poland). A small forested island separated from Gdansk by the harbour channel, Westerplatte was established as a Polish military outpost during the interwar period.
In the mid-1920s, the Second Polish Republic established the Polish Military Transit Depot (Wojskowa Składnica Tranzytowa, WST) on the Westerplatte peninsula in the Free City of Danzig. Beginning on 1 September 1939, the German Wehrmacht and Danzig Police assaulted the WST. Despite initial assessment on both sides that the Polish garrison might hold out for several hours before being reinforced or overwhelmed, the Poles held out for seven days and repelled thirteen assaults that included dive-bomber attacks and naval shelling.