1969 film by Rolf Thiele

Russian and British submarines with nuclear missiles on board both vanish from sight without a trace. England and Russia both blame each other as James Bond tries to solve the riddle of the disappearing ships. But the KGB also has an agent on the case.

A British spy ship has sunk and on board was a hi-tech encryption device. James Bond is sent to find the device that holds British launching instructions before the enemy Soviets get to it first.