Third of three episodes to feature a submarine.
There are James Bond connections here. The idea of a disgruntled Nazi firing atomic bombs on London is the plot of Ian Fleming's novel, Moonraker. Stealing nuclear weapons and demanding ransom is the essence of Thunderball and the film Diamonds are Forever, in which Joseph Furst plays Blofeld's henchman, Metz.
French title: La recherche
The submarine in the external shots is HMS Artemis