In 1943, Joseph Stalin decided to launch an arms build-up of nuclear weapons, under the charge of Igor Kurchatov ; the latter requested Stalin to relocate Zeldovich and Khariton to Moscow, in the nuclear weapons program. Zeldovich joined Igor Kurchatov 's small team at this secretive laboratory in Moscow to launch the work on the nuclear combustion theory, and became a head of the theoretical department at the Arzamas-16 in 1946.