Voyage to the Bottom of the Sea (1964)

S1E3 The Fear-Makers

Title: The Fear-Makers Plot: Following the disappearance of its sister vessel, Polidor, during a deep-sea experiment, the Seaview forges ahead with its own trials. Unbeknownst to the frazzled crew, a psychologist among the visitors is actually a saboteur who has introduced a gas that induces terror into the submarine's air supply. As Seaview descends into the abyss, an escalating wave of fear begins to grip the crew, threatening their mission and sanity.