In the building of the Czechoslovak embassy, Yugoslavia signed capitulation in June 1941, after the Axis attack in World War II. In 1943, as part of the strategic bombing campaign within the scopes of the oil campaign against Nazi Germany, the U.S. began massive bombardment of the oil fields and refineries in Romania, known as the Operation Tidal Wave campaign. On their return, as Belgrade was important strategic point, the bombers threw their unused bombs on the city. German occupational forces dug several pools across the city to storage water for extinguishing the fires. The largest such pool was built along the Bulevar, between the buildings of the Main Post Office and National Assembly, where part of the Takovska Street is today. In time, citizens began to use the pools for swimming and the Germans didn't try to stop them. In order to keep the appearance of normal life during occupation, Germans even organized a water polo match between the German soldiers and local youth. After the war, some swimming competitions were held in this pool by the new authorities, but the pool was ultimately re-filled by 1950.