The Polish Post Office (Poczta Polska) in the Free City of Danzig was created in 1920 under the Treaty of Versailles, and its buildings were considered extraterritorial Polish property.
The Polish Post Office in Danzig comprised several buildings.

As tensions between Poland and Germany grew, in April 1939 the Polish High Command detached combat engineer and Army Reserve Sublieutenant (or 2LT) Konrad Guderski (1900-1939) to the Baltic Sea coast.
With Alfons Flisykowski and others, he helped organise the official and volunteer security staff at the Polish Post Office in Danzig, and prepared them for possible hostilities.
In addition to training the staff, he prepared the defences in and around the building: nearby trees were removed and the entrance was fortified.
In mid-August, ten additional employees were sent to the post office from Polish Post offices in Gdynia and Bydgoszcz (mostly reserve non-commissioned officers).

In the Polish Post Office complex on 1 September 1939 there were 56 people: Guderski, 42 local Polish employees, ten employees from Gdynia and Bydgoszcz, and the building caretaker with his wife and ten-year-old daughter, Erwina, who lived in the complex.
The Polish employees had a cache of weapons, consisting of three Browning wz.1928 light machine guns, 40 other firearms and three chests of hand grenades.
The Polish defence plan assigned the defenders the role of keeping Germans from the main building for six hours, when a relief force from Armia Pomorze was supposed to secure the area.

The German attack plan, devised in July 1939, determined that the main building and its defenders would be stormed from two directions.
A diversionary attack was to be carried out at the front entrance, while the main force would break through the wall from the neighbouring Work Office and attack from the side.
Danzig Police also drew up plans for attacking the post office.
The Polish Post Office (Poczta Polska) in the Free City of Danzig was created in 1920 under the Treaty of Versailles, and its buildings were considered extraterritorial Polish property. The Polish Post Office in Danzig comprised several buildings.
As tensions between Poland and Germany grew, in April 1939 the Polish High Command detached combat engineer and Army Reserve Sublieutenant (or 2LT) Konrad Guderski (1900-1939) to the Baltic Sea coast. With Alfons Flisykowski and others, he helped organise the official and volunteer security staff at the Polish Post Office in Danzig, and prepared them for possible hostilities. In addition to training the staff, he prepared the defences in and around the building: nearby trees were removed and the entrance was fortified. In mid-August, ten additional employees were sent to the post office from Polish Post offices in Gdynia and Bydgoszcz (mostly reserve non-commissioned officers).
In the Polish Post Office complex on 1 September 1939 there were 56 people: Guderski, 42 local Polish employees, ten employees from Gdynia and Bydgoszcz, and the building caretaker with his wife and ten-year-old daughter, Erwina, who lived in the complex. The Polish employees had a cache of weapons, consisting of three Browning wz.1928 light machine guns, 40 other firearms and three chests of hand grenades. The Polish defence plan assigned the defenders the role of keeping Germans from the main building for six hours, when a relief force from Armia Pomorze was supposed to secure the area.
The German attack plan, devised in July 1939, determined that the main building and its defenders would be stormed from two directions. A diversionary attack was to be carried out at the front entrance, while the main force would break through the wall from the neighbouring Work Office and attack from the side. Danzig Police also drew up plans for attacking the post office.
Defence of the Polish Post Office in Danzig