Westerplatte is a peninsula in Gdańsk, Poland, located on the Baltic Sea coast mouth of the Dead Vistula (one of the Vistula delta estuaries), in the Gdańsk harbour channel. From 1926 to 1939 it was the location of a Polish Military Transit Depot (WST), sanctioned within the territory of the Free City of Danzig (now Gdańsk).
It is famous for the Battle of Westerplatte, which was the first clash between Polish and German forces during the Invasion of Poland and thus the first battle of the European theater of World War II.
The resort was established on the Westerplatte peninsula around 1830 which had a beach, a forested park, an ocean-side bath complex and health spa facilities.
In 1925 the Council of the League of Nations allowed Poland to keep 88 soldiers on Westerplatte, which the Poles had secretly increased to 176 men and six officers by September 1939. They were armed with one 75 mm gun, two 37 mm Bofors antitank guns, four mortars and a number of medium machine guns. There were no heavy fortifications, but several reinforced buildings and guardhouses equipped with heavy weapons hidden in the peninsula's forest.
The Polish garrison was separated from Free City of Danzig (Gdańsk) by the harbor channel, with only a narrow isthmus connecting the area to the mainland. In case of war, the defenders were supposed to withstand a sustained attack for 12 hours after which a relief from the main units of the Polish Army were to arrive.