
When the Nazi's attacked Warsaw September, 1939, it didn't matter if you were Jewish or Catholic or atheist, everyone worked together for weeks, hoping to hold the city against the Germans.
The Polish Army understood that Yom Kippur was the most holy day of the year for Jews and excused them that day from the crucial work of digging defensive trenches.
But German bombs had destroyed many synagogues and homes in Jewish neighborhoods so all able males, including children and old men rallied at the city’s barricades, praying the prayers for the Day of Atonement while they worked to protect their city, even as air attacks continued.
From Irena's Children, Young Readers Edition, a year later, Oct. 12, 1940

A long blast of the shofar marked nightfall and the close of Yom Kippur in Warsaw’s Jewish neighborhood. Panic gripped the Jewish community at news of the Nazi’s latest command. The Germans wasted none of their orderly methods on a system to help the nearly one in four Warsaw families ordered to pick up household and move.
Photo below courtesy Library of Congress, European Jew blows Sabbath shofar, circa 1935
At the end of the war, only 11,500 Jews had survived. Twenty-five hundred of those were children rescued by Irena Sendler and her underground network. Read that story in Irena's Children.