More than six decades after the end of World War II, the question still boggles the mind: How did they survive? After all these years, even the heroes of the story find it hard to believe that they came out alive. It was 1942 in German-occupied Poland. The Jews of Dubno, then located along the Polish border with Ukraine, were incarcerated in the city's ghetto. A Polish family of five offered to hide a Jewish family whom they knew from before the war in their home on the outskirts of the city if they felt their lives were in danger. As the Germans prepared to liquidate the ghetto that fall, eight members of the Fiszer family and seven other Jews managed to escape the ghetto, and made their way to the Kwarciaks' backyard. An army man, Piotr Kwarciak, his wife, Maria, and their three boys, aged 12 to 15, had built a well-camouflaged underground shelter beneath a pig sty nearby. The shelter was tiny, with only room to sit. But it was life. The 15 Jews would remain underground for the next year and a half, only able to stretch, stand and exercise on a small ladder in the shelter. The Kwarciak family provided the Jews with food and clothing despite the great risk to their own lives. "We knew that we couldn't say a single word to our neighbors or closest friends or we would be killed by the Germans," recalled Alfred Kwarciak, 76, who was the youngest of the family's boys, during a reunion with the Jewish family he helped save at Yad Vashem on Sunday. At first, the Jews paid for their food, but when their money ran out the Kwarciaks continued to hide and feed them, motivated by friendship, compassion, love of humanity and fervent Christian beliefs. The Polish boys stole food from summer camps to feed the 20 people in the household, and were charged with ensuring that no one came to the house. The worst was yet to come. In 1944 the Kwarciaks were also forced to take refuge in the shelter, as the front line between the approaching Red Army and the Germans approached their home. Then 12 German soldiers took up residence in the empty house, maintaining it as an observation post and command center for more than three weeks. Day and night, the house came under constant mortar and gunfire from the Soviet Army, as the 15 Jews and their Polish protectors sat hiding in the shelter and approached starvation. As the families lay huddled in darkness, mortar shells struck nearby. "Until this very day I do not understand how a mortar did not hit us," Kwarciak said on Sunday. "They say that a soldier shoots but the Lord carries the bullets. It must have been divine supervision." Hungry and exhausted, the mothers of the two families decided to leave the shelter, and came upon the German soldiers who were staying in the home. Pretending to be Poles from a neighboring house, they were able to get the soldiers' leftovers by cleaning up for them, and managed to smuggle some of the food back to their families in the shelter. Finally, salvation came. In March 1944, exhausted, starving and filthy from their stay underground - but all alive - the families were liberated by the Red Army. After the war, most of the survivors immigrated to Israel, and the Kwarciak family moved to an area within Poland's new borders. The families kept in touch. In 1989, Yad Vashem recognized the Kwarciak family as Righteous Among the Nations. "You have been in my heart since I was a young boy," survivor Michael Fisher, 80, from Kiyat Tivon near Haifa, who was a boy of 15 in the shelter, told Kwarciak. Fighting back tears, Fisher told how Kwarciak gave him an apple one day when he was in hiding. "Here, eat this," he recalled the Polish teen telling him, the memory still fresh in his mind. Fisher, who immigrated to Israel in 1946 and fought in the War of Independence, is the father of the celebrated singer Dudu Fisher. Sunday's reunion in Jerusalem, which was organized by Fisher's family for his 80th birthday, was attended by 60 family members and friends. "I want you to look around this room," Dudu Fisher told one his father's rescuers. "Most of the people sitting here today are here because of you."