Crane and the Admiral are on a mission to secure a new element that could be used to control the world. While exploring an undersea cave events occur that leave the admiral as the only survivor of the expedition and a changed man.

The Seaview investigates a strange cloud that seems to be the source of immense destruction around the world. The world has only 24 hours to live unless Seaview can crack the secret.

The Seaview is tasked with moving a series of crates supposed to contain statues dating from the time of Atlantis. Something far more sinister is in the crates and Capt Crane is the only one in a position to save the ship.

The Seaview is following up reports of a strange island being sighted when it discovers a strange egg on the ocean floor. Everyone is puzzled and excited by the find until it hatches on board.

While on patrol the Seaview is attacked and badly damaged by an unknown submarine. As the crew frantically work to save the vessel and themselves an even greater menace appears.

The Seaview is tasked with attempting a space probe launch from sea. To avoid interference a skeleton crew is manning the ship. While en route the ship encounters a strange object that unleashes a threat that could destroy Seaview and all on board

The Seaview is tasked with transporting an Egyptian mummy from a New York museum for special secret testing. It becomes apparent very quickly not all is as it should seem, and soon a terrible threat is unleashed on the crew of Seaview.

Captain Crane discovers and captures a real mermaid. Everyone is interested in what the specimen might reveal until its mate turns up looking for revenge.

While on routine patrol the Seaview begins to hear strange noises coming from an undersea canyon. Investigating they discover the source of the noise and the power behind the destruction of a British fleet in the area 200 years before.

A Norwegian scientific installation makes contact with an alien intelligence. The Seaview goes to investigate and ends up in a life and death struggle after the alien invades the sub.

The Seaview encounters a strange structure on the sea floor. Investigating they discover a German submarine from WW2. Surviving Germans on-board think the war is still being fought. And they have weapons on-board of unimaginable destructive power.

While on a routine scientific expedition Capt Crane encounters a strange hybrid seaweed humanoid creature. Crane is captured by the creature and the crew of Seaview launch a desperate attempt to rescue Crane before his air runs out.

While racing to the aid of a ship the Seaview suffers a critical engine failure. While doing repairs Admiral Nelson suffers a critical dose of radiation which affects him in a most unexpected way.

An unfriendly government shoots down a cargo plane carrying a new top secret bomb. The race is on to retrieve the bomb and avoid detection from the enemy before the bomb can be accidentally exploded.

A scientist in an underwater sea lab has created a new form of plant life. His twin brother, who can control him telepathically, is on his way there via the Seaview, with plans of using the new plant creatures for his own sinister purposes.

Strange sounds and events begin to be reported on board the sub. While still coming to grips with the crews edginess, the Seaview encounters a strange 17th century warship that fires on the sub.

Space aliens led by an entity which takes the form of a deceased WW2 officer acquaintance of Nelson's invade the Seaview, intending to reactivate an underwater atomic base to acquire its energy.

Admiral Nelson wanders the Seaview and finds it abandoned except for Captain Crain and Chief Sharkey. He has no memory of what happened before or what the strange sounds over the intercom mean. Capt. Crane is also trying to kill him.

A controversial filmmaker's crew is killed by a creature on a remote island. The Seaview goes to investigate the incident. One of the crewmen has a special interest in the mission as his father was one of the victims.

An emergency mission leads the Seaview to rescue Kowalski's brother Stan. Once on board, Stan's refusal to help anyone else threatens the sub's survival after it sinks to the ocean floor, a thousand feet below it's crush limit.

An alien being, capable of impersonating any member of the crew, gets on board the Seaview. He plans to use the Seaview's missiles to start a nuclear war and thereby make the Earth ready for conquest.

An old man, adrift at sea, is rescued along with a sack of toys by the Seaview. The toys take on a life of their own and begin to sabotage the ship. The toys appear to be connected to an alien space ship lying on the ocean floor.

The Seaview's diving bell is driven by a tsunami onto a tropical island where a mysterious mist causes the survivors to see imaginary people and creatures.

After the arrival of a newly elected U.S. Senator to inspect Admiral Nelson's new weapon, strange things begin to happen, culminating with the realization that everyone outside of the Seaview appears to have disappeared from the Earth.

Scientists on a tropical island are measuring the radioactivity of a volcano when they are attacked by a wolf. Prof. Hollis shows signs of lycanthropy and threatens everyone on board, especially Admiral Nelson, whom he has infected.

A strange intelligent organism is found at the bottom of the ocean. Once brought on Seaview the real threat the creature represents is realized. Suddenly every life on board the Seaview is in danger.