Admiral Nelson and a Soviet scientist are in a diving bell when the vessel is swallowed by a giant whale. With only 90 minutes of oxygen, Captain Crane, Kowalski, and Riley swim into the whale's mouth to attempt a harrowing rescue.
The Chinese have developed a way to turn a human body into an intense bomb. They intend to infiltrate the Soviet Union and create a diplomatic incident that will draw the US and Soviets in nuclear annihilation.
A message is received from a US sub presumed sunk in the last months of WW2. The Seaview is sent to try and locate a cave that is mentioned in the message and to try and rescue the 5 men believed to be still alive.
Captain Crane is in Venice to meet a secret agent when she is killed. It is believed she had knowledge of a new secret Soviet weapon, and how to combat it. Crane's mission is made more complex when he is accused of the agents death.
Admiral Nelson is contacted by an agent claiming to be from the Office Of Naval Intelligence. He gives Nelson a cryptic message that the current nominee must not be allowed to become Secretary of Defense, no matter what it takes.
The President of the United States is visiting a new underwater installation when a power interruption freezes all communication. To complicate the situation they discover there is some sort of beam weapon stopping any of the safety over-ride mechanisms from activating.
A research team are taking measurements of an underwater eruption. They discover a fissure that appears to lead all the way to the Earth's core. While the discovery is exciting, what exists in that fissure could lead to deadly consequences.
Nelson and the Seaview witness the detonation of a new bomb developed by the Chinese. No bigger than a milk carton, it creates a blast 20 miles across. An American scientist who had defected to the other side steals it for his use.
A manned probe is returning to Earth when it is suddenly caught in the grip of a strange force and destroyed. Investigations point to a secret Chinese installation being responsible. Capt Crane is tasked with locating the base and destroying it.
Word comes through that Dr Liscomb has been kidnapped by a foreign agent posing as a toy importer. Liscomb has cracked the secret of the X factor, a new ingredient and everyone wants it.
Admiral Nelson is under pressure when a drone sub system he pioneered malfunctions and fires three missiles at New York City. The race is on to establish what went wrong and how to stop it happening again.
In 1978, the first space probe to Saturn returns and the Seaview is sent to retrieve it. Despite their stringent decontamination procedures an alien life form survives and, once inside, begins to take over the ship.
Admiral Nelson and Chief Starkey are marooned on an island with prehistoric creatures. The Seaview is trying to rescue them but they have an undersea monster of their own to contend with.
By air Nelson and Crane pursue a mysterious submarine stealing nuclear missiles. Their craft is shot down and Crane is captured. Nelson, recovered by a Navy destroyer, is bent on destroying the sub, not realizing Crane is on board.
The Seaview rescues two men apparently lost at sea. They are actually escaped prisoners who try to take over the Seaview. The situation is complicated by the presence of a giant sea monster attacking the ship.
The Seaview finds a sunken German U-boat while mapping the ocean floor. Sunk during WWI in the north Atlantic, it is now somehow in the south Pacific. Its captain boards the Seaview with Capt. Crane as his prey.
A meteor storm ignites atmospheric gases in the southern hemisphere. Adm. Nelson believes one of the Seaview's missiles can extinguish it but someone on board is secretly trying to stop him.
The Seaview is returning to the location of a sunken ship to recover its secret cargo. There are a number of other sunken ships in the area, and the thing responsible for all of them soon threatens the Seaview.
The construction of an undersea canal is about to start with the Seaview tasked with placing the first charge, a 50 megaton nuclear bomb. But as it is being lowered an enormous whale swallows it and swims off.
Everyone but Nelson and Crane are removed from the Seaview and replaced by 8 civilians to test new equipment. One of them is a foreign agent who wants to kill everyone on board and use the ship to provoke an incident and start a war.
A test submarine carrying a load of experimental fuel is disabled and lying on the ocean floor. The Seaview is sent to recover the volatile fuel canisters but an enormous underwater spider threatens to destroy them.
While Adm. Nelson is away, Capt. Crane tries to prevent Dr. Borgman from implanting human DNA into marine animals to create a new type of undersea creature.
While assisting an undersea drilling operation, Capt. Crane and the Seaview become locked in a life-and-death struggle with an android, powered by a new source of limitless energy, Subterranium 116.
Captain Krueger returns and once again wants Captain Crane's body. He threatens to kill everyone on the Seaview if Admiral Nelson doesn't shoot Crane and deliver his body to him.
