A sophisticated electronic method of pinpointing the position of a submerged nuclear submarine by tracking its wake, a technique explained by Q (Desmond Llewelyn) after the disappearance of the British nuclear submarine Ranger in The Spy Who Loved Me. Q compares it to using an infrared satellite to track the tail fire of nuclear missiles.

Billionaire shipping magnate Karl Stromberg (Curt Jurgens) has enlisted a scientific duo—Dr. Bechmann (Cyril Shaps) and Professor Markovitz (Milo Sperber)—to develop a heat-signature recognition system that Stromberg uses to find and trap three nuclear submarines. However, Stromberg’s system is betrayed by his secretary (Marilyn Galsworthy), who tries to make a fortune by selling the system on the open market. The ploy eventually leads James Bond (Roger Moore) and KGB major Anya Amasova (Barbara Bach) to Stromberg’s Atlantis hideaway off the coast of Sardinia.