The Tzrifin Underground, officially the Kingdom of Israel (Hebrew: מלכות ישראל, Malchut Yisrael), was an underground Jewish militant group1 active in Israel in the 1950s. "Kingdom of Israel" was the name that the group's members used, but it was better known to the Israeli public as the "Tzrifin Underground", after the Tzrifin military base, where its members were put on trial. The group carried out attacks on the diplomatic missions of the Soviet Union and Czechoslovakia in protest against those countries' antisemitic policies, such as the Slánský trial and the Doctors' plot. They also attempted to assassinate German Chancellor Konrad Adenauer with letter bombs, and occasionally shot at Jordanian troops stationed along the border in Jerusalem. The group's leader, Yaakov Heruti, recruited former Lehi colleagues, as well as adolescents from Revisionist Zionist homes who had been brought up to see Lehi fighters as heroes. Separately, another Kingdom of Israel member, Yaakov Blumenthal, "organized another clique of activists in Jerusalem, most of whom were Orthodox Jews". The group never had more than two dozen members.