The years between 1919 and 1939 were the period of the Free City of Gdańsk. After World War I, Gdańsk (or Danzig as it is called in German) was given the status of a Free City under the protection of the League of Nations. The city was separated from Germany.
A Polish post office operated in the harbour of Danzig, from which stamps, destined for Poland, were issued. Most of these stamps were existing Polish postage stamps overprinted "PORT GDANSK". The office remained open until the outbreak of World War II.
Port of Gdańsk
League of Nations
Free City of Danzig