Victims of Bloody Sunday of Bromberg.

 Victims of Bloody Sunday of Bromberg.

This german catholic priest of the Church of the sacred Heart of Bromberg (today: Bydgoszcz/Poland) in silent prayer in front of the bodies of massacred ethnic-german civilians, Bromberg september 3rd-5th 1939.

Bloody Sunday (German: Bromberger Blutsonntag; Polish: Krwawa niedziela) was a sequence of events that took place in Bydgoszcz (German: Bromberg), a Polish city with a sizable German minority, between 3 and 4 September 1939, during the German invasion of Poland.

After German Selbstschutz snipers fired on retreating Polish troops, there was a Polish reaction against the German minority and then the retaliatory execution of Polish hostages by the Wehrmacht and Selbstschutz, after the fall of the city. All these events resulted in the deaths of both German and Polish civilians. 

The Polish Institute of National Remembrance found and confirmed 254 Lutheran victims, assumed to be German civilians, and 86 Catholic victims, assumed to be Polish civilians, as well as 20 Polish soldiers. Approximately 600–800 Polish hostages were shot in a mass execution in the aftermath of the fall of the city as a "revenge".

After the Germans took over the city, they killed 1,200–3,000 Polish civilians in retaliation, as part of Operation Tannenberg. The event and place of execution became known as the Valley of Death.

 The murdered included the president of Bydgoszcz, Leon Barciszewski. Fifty Polish prisoners of war from Bydgoszcz were later accused by Nazi Sondergericht Bromberg summary courts for taking part in "Bloody Sunday" and shot.

The term "Bloody Sunday" was created and supported by Nazi propaganda officials. An instruction issued to the press said, "... must show news on the barbarism of Poles against Germans in Bromberg. 

The expression 'Bloody Sunday' must enter as a permanent term in the dictionary and circumnavigate the globe. For that reason, this term must be continuously underlined.

This topic of WW2 history is still a matter of dispute.

The exact number of victims of Bloody Sunday is disputed. Peter Aurich (a pseudonym of the German journalist Peter Nasarski) put the number of German civilian deaths in Bydgoszcz at 366, while Hugo Rasmus estimates it as at least 415.

 Two Polish historians, Włodzimierz Jastrzębski and Czesław Madajczyk, estimate ethnic German deaths at 103 (Jastrzębski), and about 300 (150 on September 3, the rest in the days after). 

The Polish historians point out that since these losses occurred during actual combat, most of the civilian losses should be attributed to accidents common in urban combat conditions; they argue that civilian losses might have occurred when the town was attacked by the German air force (Luftwaffe). Strafing of civilians in the town by the Luftwaffe is confirmed by German witnesses.