1924 – The League of Nations grants Poland Westerplatte peninsula for storage and shipment by rail of imported materials. The storage is named Military Transit Depot at Westerplatte It becomes a Polish exclave, surrounded by German-dominated Free City of Gdansk.
January 1926 – the first Polish guard unit arrives at Westerplatte. The Depot is surrounded by a brick wall, new port infrastructure and warehouses are built.
1933 onwards – construction of permanent fortifications: four guardhouses with concealed basements that contain heavy machine guns, fortified posts in the NCOs’ mess and in the purpose-built, modern, bomb-proof Barracks.
A network of field fortifications/outposts is built that protects the Barracks (Wał, Prom, Fort, Deika, Elektrownia, Przystań, Łazienki). This cleverly designed system of defences causes many casualties among the attacking German platoons.