Mission: Impossible - The Bunker (1969)

Dr. Erich Rojak, a brilliant scientist, is being held in an underground bunker containing a laboratory where he is forced to work on a small but extremely powerful long-range missile. If he succeeds, the missile has the potential to change the balance of power between the East and the West. Rojak is cooperating only because his totalitarian government is holding his wife, Anna, and threatens to kill her unless he completes the missile. The IMF's assignment is to rescue Rojak and his wife and to destroy his missile research. But another unfriendly government has sent professional killer Alexander Ventlos to make certain Rojak never completes his work.