 Two of his uncles were Joseph Katznelson, a companion of Ze'ev Jabotinsky and one of the Irgun's two Chiefs of Illegal Immigration and Avraham Katznelson, one of the signatories of the Israeli declaration of independence, and his aunt was Rachel Katznelson-Shazar, wife of Zalman Shazar, the third President of Israel.Shmuel joined Etzel in 1938 and after the declaration of the Revolt in February 1944, and took part in operations against British targets, most notably the 26 February 1944 attack on income tax offices in Jerusalem.In 1944 he was a commander of the Jerusalem District and commanded the operation that blew up the Income Tax offices in the city; Commander of Intelligence in Jerusalem District.