He was a Sonderkommando[citation needed] at the Treblinka extermination camp and participated in the unit's planned revolt in August 1943.

His father, Perec Willenberg, was a teacher at a local Jewish school before World War II, a talented painter and visual artist.

[1][2] In the course of the Nazi German invasion of Poland, on 6 September 1939 the 16-year-old Willenberg set off in the direction of Lublin to join the Polish Army as a volunteer.

[5] The Jews deported from Silesia were brought there, and an epidemic of typhus broke out, due to overcrowding and poor sanitation.

Willenberg traded his father's paintings for food and other necessities, but also worked at a steel mill in Starachowice for several months, along with hundreds of forced laborers supplied by the Judenrat.

[6] In 1942, the Nazis began their secretive Operation Reinhard — a planned extermination action of Jews in the semi-colonial General Government district — marking the most deadly phase of the Holocaust in Poland.

But on 20 October 1942 Willenberg was forced to board a Holocaust train along with 6,500 inmates of the then-liquidated Opatów ghetto, and was sent with them to the extermination camp at Treblinka.

[13][14] Upon his arrival at Treblinka, Willenberg received a life-saving piece of advice at the unloading ramp, from one of the Jewish Auffanglager prisoners.

[1] Luckily, he was wearing a paint-stained smock-frock of his father's (an outer garment traditionally worn by rural workers), donned in Opatów in preparation for slave labor.

Among their tasks was weaving tree branches into the barbed-wire fences in order to hide the grounds, buildings and lines of prisoners.

Wounded in the leg, he journeyed back to Warsaw, where he managed to find his father, who was hiding on the "Aryan" side of the city.

[3] In his memoir, Revolt in Treblinka, Willenberg wrote that on the first day of the Uprising he joined Batalion Ruczaj of the Armia Krajowa Sub-district I.

[citation needed] At the beginning of September 1944, he transferred to the Polish People's Army with the rank of cadet sergeant.

[18] Willenberg took up training as an engineer surveyor and obtained a long-term position of Chief Measurer at the Ministry of Reconstruction.