Two actors played the character 'Dr Gamma'. Werner Klemperer and Theodore Marcuse. The transition from Klemperer to Marcuse happens 35 minutes in. Only Klemperer's face was slightly shown though only Marcuse is listed in the credits.
To thwart the attempt by the crew of the Seaview to stop the earthquakes that will destroy the North Atlantic coasts, the leader of the terrorist group sends an unmanned drone to blow up the rescue party. This was filmed in 1963, 50 years before the U.S. used them in the Middle East.
The helicopter during the opening sequence is a Bell 47G-2, probably the most famous rotary wing aircraft of all time.
This episode was shot in color but aired in black in white. It would not be seen in color until the series was released on DVD.
This episode takes place in the 1970s.