"Idiots!!!" Admiral Nelson to himself. There is an imposter on Seaview. Lee Crane is the main suspect. Admiral Nelson takes Morton and Sharkey into his confidence. They must put Crane to the test to find out whether or not he's the man they know. Captain Crane is really put through the ringer in this episode! Admiral Nelson hurts his feelings on purpose, the Captain practically chokes to death from a fire in the Circuitry Room that he gets blamed for, he gets locked in a storage room, and he's driven half out of his mind by the Admiral, Morton and Sharkey. Through it all, Crane maintains his inner belief in himself.

As Admiral Nelson demonstrates a new tracking device for a visiting U.S. senator, it seems to show that Seaview is the only life left on earth.

Seaview and an enemy sub battle to recover a superbomb from the ocean floor.

In an attempt to control the planet's tides, Dr. Randolph Mason (a nut if ever there was one -- he is part scientist, part make-up artist!) has invented a powerful electromagnet and established a magnetic field around the moon. The only person who seems to recognize the obvious danger in this silly plan is Harriman Nelson. At first glance, it would appear that Nelson has killed Dr. Randolph. At second glance, it would appear that Captain Crane has betrayed the Admiral. On third glance, the moon is getting closer and closer to Earth, and will soon collide with our beautiful blue orb -- unless the Seaview can save the world. Again. * In this episode, we learn that Chief Sharkey attended Lincoln High in Coney Island, Brooklyn, New York. (There actually is a Lincoln High in Coney Island.

Drs. Paul Ward and Peter Omir have discovered a powerful new element -- Subterranium 116. This element can produce limitless pure energy, but Omir may have another agenda.

"Those who see the Flying Dutchman never, never reach the shore." Investigating the loss of Navy ships, Nelson finds an ancient dagger in a cave on an uncharted island, and falls under a strange curse. Haunted by visions of skeletons and an anachronistic ship, he has trouble convincing the crew of his sanity. Meanwhile, Seaview is sailing in circles, and the visiting Commander Van Wyck seems to have disappeared. Guest star Warren Stevens also appeared in "The Saboteur" and "Deadly Invasion".

Cybernetic genius Tabor Ulrich creates a perfect mechanical duplicte of Admiral Nelson. His plot: to make the crew of the Seaview they are fighting World War Three. In doing so, the sub will launch nuclear missles at the China, Russia and the USA. After the holocaust, Ulrich plans to take over and usher in "the age of the cyborg".

Things go wrong when Nelson and Crane test out a new automated system for Seaview.

Crane is caught up with a circle of spies as he tries to make his way back to Seaview with important missile defense data.

A foreign power is salvaging sunken nuke missiles from the ocean floor to make themselves a superpower.

Seaview encounters a sunken WWI sub...with someone still left aboard.

finds herself suddenly out of touch with the rest of the world, in the wrong part of the ocean and encountering strange creatures. It seems she's been thrown a million years back in time. Then the Admiral opens his cabin door and finds himself back in his Santa Barbara office, confronting the strange Mr. Pem and his pocket-sized time machine, and has to play a risky game before time can return to its normal course. The early part of this episode contains two astronomical errors. First, Nelson takes snapshots of the eclipse-darkened sky with an ordinary camera, but when the shots are developed they show galaxies and nebulae that could only be seen with a telescope. Second, the Admiral describes the pictures as showing 'constellations'. Henry Jones (Pem) also appears as Sprague in "Night of Terror" and once again as Pem in "No Way Back". This episode features re-used footage from "Thing from Inner Space".

"... but the Flying Sub's my baby!" Captain Crane to Chief Sharkey Seaview's reactor is running wild -- again. Without taking the time to don protective anti-radiation gear, Captain Crane runs into the Reactor Room to shut down the pile. An explosion renders him unconscious. Although treated in Sickbay with a special anti-radiation device, the Captain does not come out of his coma-like state. Doc can find no explanation. (Apparently, Doc hasn't read the script.) Corpsman Mallory has turned that life-saving device into a time-machine. Mallory is testing his fourth-dimension gadget on Crane before using it to enslave the entire world! A warped and insane Captain Crane from the future shoots and kills Admiral Nelson, because he believes the Admiral has held him back from achieving all he should have. Maybe he's paying Nelson back for the Krueger incident.

Seaview experiences a sudden power overload and blows up, killing all hands aboard. When Admiral Nelson (who was at the Nelson Institute at the time of the accident) hears of the destruction of the Seaview, he gets an impossible to refuse offer from Mr. Pem (who survived from A Time To Die): in exchange for the use of the sub's nuclear reactor, Pem will transport Nelson back in time to before the explosion which destroyed Seaview. Once back in time, Pem renergizes his time travel device and brings the sub back even further in time to the American Civil War. Before the crew has time to absorb this, the ship is boarded by Major General Benedict Arnold! Now Nelson has to stop Pem's far-reaching plan to take over the world and avoid the explosive disentergration of Seaview.

Nelson is injected with a radioactive material that makes him a walking time bomb. This episode marks the first appearance of the FS-1!

A space probe returns to earth and is recovered by Seaview...only to unleash an alien organism aboard.

Bainbridge Wells is filming a segment of his "Science On The Move" television series on a small island off the coast of Chile. A sea creature comes ashore and kills his crew. Wells convinces Admiral Nelson to return to the island because he wants to prove that the creature really exists. Crewman Patterson has a special interest in the mission.

The Seaview is being buffeted about by underwater explosions due to the eruption of an active volcano. Dr. Turner (Victor Jory) is aboard to stop the eruptions. However, his true mission is to bring up ""elixir stones."" An alchemist, Turner needs the stones to keep him immortal. However, in order to bring up the stones, he needs to stimulate the volcano into full eruption!

Seaview is on the lookout for an enemy sub and its underwater sub-pen. Sonar picks up a contact. The rogue sub fires at Seaview, which is saved only by virtue of her new electronic hull shield. Not so fortunate is Captain Crane, who has just located the sub-pen while on patrol in the FS-1. A powerful laser fires a beam at the Flying Sub, crippling the ship. Running out of air, moving in and out of consciousness, Crane is unable to give the pen's coordinates to Nelson. Thanks to the hard work of some enemy agents aboard, Seaview seems unable to rescue the Captain. Worried about Crane trapped in the Flying Sub, Admiral Nelson is particularly impatient in this episode. He constantly barks at Morton and the Chief.

While inspecting undersea bomb shelters with the President, aides attempt a power grab.

Nelson and crew are invited to a marine scientist's undersea lab for a visit but there is giant sea life in the way.

Seaview is investigating a thousand-mile wide communication blackout. The source of this is a large alien brain found under the sea. It is broght aboard and takes over visiting scientist, Dr. Lindsay. With his help, and after possessing Captain Crane, the alien vows to take over the Seaview and after that, the Earth.

Captain Crane rescues a diver from a wrecked atomic sub. He turns out to be Kowalski's brother, Stan, a Navy diving specialist. When the Seaview needs his help in getting off the ocean floor, Stan is not up to the job.

The crew of a lost submarine returns as rock men to menace the Seaview. A new man, Kowalski's friend Richards, is captured on a diving mission and turned into a Fossil Man. Nelson is then ordered to turn command of the Seaview over to these rock men. Will Nelson comply? Will the crew be dipped into the transformation lava to exist as living rock?

The Seaview is en route to rendezvous with the fleet when Sharkey reports a missle fuel leak. Crane and Morton believe it's worth returing to port to repair, however Nelson knows how to handle it. Taking a small breathing device with him, the Admiral locks himself in the compartment in question to effect repairs. However, he drops a wrench, the circuts blow and Nelson is knocked out. When he comes to, he's gripped by paranoia which worsens with each passing minute. Trusting no one, Nelson loses his grip on reality, arresting Doc, fighting with Sharkey and finally launching a nuclear missle at the fleet!