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!

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

Seaview comes to the rescue of newly discovered WWII survivors living in an underwater cave beneath a rumbling volcano.

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".

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

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

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.

Defecting scientists create a proton bomb, but are killed by a foriegn power and the bomb is captured. A surviving scientist works at disarming the bomb...with other plans in mind.

Asian powers attempt to interfere with the American Space Program.

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

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

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

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

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

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.

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

Cruising for days under the ice, Seaview surfaces to find the sky is ablaze thanks to the Van Allen belt catching fire. Nelson races to Washington to confer with fellow scientists and hatches a plan to detonate a nuclear device into the atmosphere and extinguish the fire. Weber, a Fellow scientist, feels they should do nothing and allow the fire to burn out. Nelson disagrees and takes Weber and two others aboard Seaview to decide the course of action as the sub races to the firing point. However, Weber is determined to stop Nelson and is willing to kill to do it!

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.

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.

A 16th century pirate seemingly comes back from the grave to threaten Seaview.

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

Captain Gantt, an ego-maniacal scientist, is in a nuclear sub testing a powerful new fuel. Due to his bungling, the sub crashes into a giant web and is attacked by a monsterous sea spider. The Seaview investigates and rushes to retrieve the remaining fuel canisters before the enormous underwater pressure collapses the test sub abd detonates the fuel - an explosion which would kill millions!

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.

Captain Krueger returns to compel Nelson to shoot Crane. Once that is done, Krueger takes over Crane's body and searches out a host for Lani, Krueger's dead lover, so the two can be reunited. Can Admiral Nelson save his friend and end the plans of the evil Captain forever?