The Seaview takes on a skeleton crew and is being used to guide a new interstellar space probe. However, Chip Morton is taken over by an alien shadow man which wants to stop the probe.

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.

A newly installed super-computer is tested on the Seaview...but the enemy has other plans.

An undersea earthquake exhumes hundreds of strange metallic capsules, and a powerful humanoid creature who could destroy mankind is restored to life after millions of years in suspended animation.

A gigantic tidal wave will destroy much of the civilized world, but Admiral Harriman Nelson has a plan to stop it -- Seaview will set off a nuclear explosion at precisely the right time and place. Evil forces seek to destroy Nelson before he implements his plan -- in the chaos following the tidal wave, they hope to take over the world! Seaview's original Skipper is killed and it's Lee Crane from the US Navy to the rescue.

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

A submerged domed island is forced to the surface by its volcano and exposes a Jurassic-style world.

A missile defense platform-drone malfunctions and threatens to destroy the East Coast of the US.

A husband and wife Antarctic research team is killed by an experiment on plankton gone wild. Seaview arrives to investigate and take plankton samples. Soon the submarine is in danger of succumbing to the horrible, slimy growth. Nelson, Crane and crew face another problem: one of the three scientists on board the sub is an enemy agent.

A lush, tropical, verdant paradise in the South Pole? Living dinosaurs? Such fanciful ideas must surely be the ravings of a madman. Or perhaps not, as Admiral Nelson soon discovers. The question is, will he and Crane survive their trip to a lost world?

While investigating the disappearance of research ships in the Aegean, the Seaview is damaged by a bomb. Captain Crane goes ashore, and pretends to be a diver for hire. The Captain meets an ex-diver, now a mute due to a tragic accident, who claims to have seen a ""city beneath the sea"". Crane gets hired by the ""bad guy"", but his cover is soon blown. He is taken prisoner and nearly loses his life.

Seaview rescues two men adrift at sea, only to discover they are escaped prisoners intent on not returning to prison. While they attempt to hijack the sub, an undersea creature surfaces to menace the Seaview.

Two scientists examining a radioactive volcano are attacked by a wolf. One dies, and the survivor is infected by a virus that causes him to change from man to werewolf and back again. Admiral Nelson is exposed to the virus and the crew must find a vaccine.

After Seaview's sister ship, Polidor, is lost on an experimental deep dive, Seaview continues with the tests. Unknown to the already stressed crew, one of the visiting psychologists aboard is an enemy agent who has released a fear-causing gas into the air system. As Seaview plunges into the depths a dangerous panic starts to spread.

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

A Soviet satellite has crashed into the sea and its nuclear reactor must be disarmed before it causes a disaster. Two Soviet scientists come aboard Seaview to carry out the work -- but one of them is an imposter.

A mad art connoisseur seizes control of the Seaview and plans to pirate Leonardo da Vinci's Mona Lisa from a French Ship bound for the World's Fair.

An alien spaceship lands in the ocean, and Seaview is sent to investigate. Although Seaview is powerless in the vicinity of their ship, the aliens seem friendly, and Nelson manages to open negotiations. The military authorities, however, have other ideas, and Seaview may be in as much danger from human interference as from the aliens.

When a mass missile launching by a foreign power sets the U.S. on nuclear alert, the Seaview goes into a fail-safe maneuver, but is the launch really what it appears to be, and does this actually mean it's "doomsday?"

On a rendezvous mission, Crane and several crewmen are drugged into unconsciousness on a deserted yacht. Waking up in a South American prison, the men are taken out to the courtyard, one per hour, and executed. All will die unless Crane breaks his oath and confesses what he cannot. Will Nelson's rescue mission succeed? Will the country in question survive the machinations of the evil man who wants to take over?

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

Dr. Alex Holden is hunting a gigantic whale in which he has injected an experimental growth serum. It turns and destroys his boat, killing his crew. He is rescued by Seaview, which was on en route to plant a nuclear device to blast an undersea channel Holden obsesses over getting his swallowed equipment from the whale when it turns and comes at the sub, swallowing the bomb as it is being lowered! Nelson cannot detonate the bomb, as the president's carrier is in the area. The nearly insane Holden steals Nelson's remote detonating device and threatens to blow up the whale if he's not permitted to get samples of the whale.

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".

A sea monster kills three villagers in a Norwegian fjord; however, one man survives. Seaview arrives to investigate. Nelson and Crane are met with hostility from the locals and find the survivor has died. Nelson does his best to make sure the ""sea monster"" doesn't destroy Seaview.

Faceless aliens invade Earth and try to take over an underwater atomic base. The leader takes the form of an old, deseased friend of Admiral Nelson in order to convice Nelson they mean no harm. Nelson will have none of it and leads a landing party to the base to stop the aliens, even if the cost includes their own lives.

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.

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.

A scientist and his secretary come aboard Seaview when their research vessel is sunk by a giant Portugese Man-Of-War. They want Admiral Nelson to return to the scene, but won't tell him the real reason.

Injured in a fall, the President of the United States is in desperate need of surgery -- and the operation must be kept secret. Naturally, Seaview is chosen as the best place for the operation. An enemy agent, taking the place of the doctor who would have used a radiological device on the President, will attempt to kill the Commander-in-Chief with a deadly ray. Will she be discovered in time to save the President?

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!

Aliens are at it again. They're planning to destroy the Earth. However, one of the aliens claims to be a good guy. Can he be believed? Will mankind survive yet another close encounter with space visitors? * Skip Homeier also appears in "The Amphibians" and "The Day the World Ended" * Kevin Hagen guest-starred in "The Shape of Doom".

Admiral Nelson and Captain Crane are involved in a mind-control experiment, with Chief Sharkey caught in the middle.

Crane is brainwashed by enemy agents, and his new mission is to deactivate certain strategic undersea missiles and to assassinate Admiral Nelson!

A mysterious cloud is enveloping the Earth and causing massive Tsunami and other catastrophic environmental damage. Crane takes the flying sub in to find out the cause and is taken over by an evil alien. Once aboard, this alien tries to stop Nelson before he can destroy the cloud with nuclear weapons.

An old friend of Nelson's comes aboard Seaview to continue his research into the giant whale that destroyed his ship, crippling him and killing his son. His real motives, however, have more to do with vengeance than science, and Crane becomes concerned that the Admiral is caught up in his friend's obsession.

A toy manufacturer is involved with kidnapping and shipping politicians and scientists to foreign powers.

About the plot . . . Um . . . Well . . . Uh . . . Okay, here it is: You see, there are these twin leprechauns, one good, the other icky. The icky one wants all the gold that's buried beneath an underwater defense installation in the Irish Sea. The good leprechaun does his best to stop his evil brother from doing any harm . * Footage of Morton and Kowalski trapped in an underwater cave was borrowed from previous episodes. So what else is new? * Why this episode wasn't broadcast on St.

A lobster-like alien emerges from a capsule retrieved from the ocean floor. He claims that all he wants is one of Seaview's nuclear rods to power his ship for the homeward journey, but neither Captain Crane nor Admiral Nelson is convinced he can be trusted. Victor Lundin also played the neck-braced Hansjurg in Season 2's "The Menfish".

"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".

Arctic Listening Station XZ-5 receives a message from a voice from space (""laser beeeeeam""). Professor Bergstrom, ignoring the advice of his assistant, activates their beam and brings the alien, living flame, to Earth. Now, this Heat Monster wants the Seaview to detonate a bomb under the polar ice cap. How can the intrepid crew defeat this new menace?

Nelson works on finding an assassin before he can kill the new Secretary of State.

With Admiral Nelson away, his old friend Admiral Park takes over Seaview's current mission. Dr. Borgman is conducting experiments, and Park suspects he is up to no good.

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.

The ghost of Blackbeard is alive and well, and he wants the Seaview and her crew. The pirate 'drafts' Kowalski, who makes a very convincing and quite blood-thirsty buccaneer. Nelson and Crane have their hands full trying to protect the President of the United States (a guest of a Middle Eastern Shah on a nearby yacht), and regain control of their ship.

Seaview is under polar ice, trying to discover the cause of increased flooding around the world. Nelson finds out that Frost Men are in the process of melting the ice cap. The Seaview's reactor is just what they need to finish the job.

As World War II draws to a close, a secret underwater Nazi base is damaged during a sea battle. A Nazi scientist and his aide are accidently put in suspended animation. Thirty-five years later, the crew of the Seaview discovers and revives them. The Nazis attempt to carry out their interrupted mission: destroy the capital cities of the Allies.

Aliens snatch a manned space probe launched from Seaview with Chip Morton aboard, and transport it at the speed of light to their observation post on the rocky, unstable surface of Venus. Checking out the duplicate capsule, Crane suffers the same fate before he even has time to launch. With Chip blinded and a prisoner, and the planet's surface due to undergo catastrophic quakes in a few hours, the odds seem to be against the two men.

Nelson is stranded aboard a life raft with the ex-premier of a hostile foreign power who carries vital information on a plot to destroy the free world.

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?

Admiral Nelson has been brainwashed. After getting a vital energy source, he attempts to kill Crane and the visiting Dr. Land in an undersea cave. He then returns to the sub, gasses the crew and sets the reactor to blow. Can Crane recover and return to the Seaview before Nelson can destroy it?

The Seaview is called in to help track an artificially created life form, now loose in the Pacific. The creature, which is growing at a fantastic rate, has its own agenda -- starting with a takeover of the crew.

The Seaview crew is being entertained by puppet cairactures of the Captain and Admiral, compliments of Professor Multiple. Multiple remains on-board when the sub departs, and his dolls soon come to life, replacing their real-life counterparts. Only Nelson and Crane avoid capture and transformation. Multiple boasts that he and the others are all puppets, created by machines from the future that have traveled into the present, and need the Seaview as a new host body. Can Nelson and Crane overcome this fantastic threat?

A UFO crashes and an alien assumes the form of Admiral Nelson.

While racing to help a foundering research vessel, the Seaview's nuclear reactor goes critical. Admiral Nelson's right hand is exposed to intense radiation as he fixes the problem, causing a flare-up of the "werewolf" virus that he carries.

Seaview has been sent to the ocean floor by mysterious pressure impacts. Crane, Sharkey, and Kowalski go out in the Flying Sub to investigate. They, too, are sent to the bottom of the sea. Strange creatures (half men-half fish) present themselves and explain that they intend to take over Seaview (who doesn't?) and eventually the world! Don Matheson starred as Mark Wilson in Land of the Giants.

After Nelson's experimental submarine is attacked by a giant jellyfish, tension mounts aboard the Seaview as Nelson exhibits signs of a mental breakdown.

The Seaview is on a joint mission with Russian scientists to salvage the remains of a Soviet undersea lab. While a scientist is being lowered in the diving bell, a giant whale arrives and rams the bell. The glass is shattered, killing him. Nelson and the remaining Russian scientist, Katya Markova, go on a second dive. The whale reappears, this time swallowing the diving bell whole! Now it's a race against thime as Captain Crane and the crew of the Seaview find the diving bell and get it out before Nelson and Markova run out of oxygen!