Lost in a mysterious fog while at sea, Ocean Pioneer explodes without any apparent reason. It is only after a replacement vessel has been built and sent on an identical mission that Brains discovers that the cargo becomes highly explosive in the presence of a certain variety of sea algae.
- Main article: Danger At Ocean Deep/Storyline
- Main article: Danger At Ocean Deep/Transcript
- Jeff Tracy - Peter Dyneley
- Scott Tracy - Shane Rimmer
- Lady Penelope Creighton-Ward - Sylvia Anderson
- Virgil Tracy - David Holliday
- Alan Tracy - Matt Zimmerman
- Brains - David Graham
- Parker - David Graham
- Tin-Tin Kyrano - Christine Finn
- Gordon Tracy - David Graham
- John Tracy - Ray Barrett
- Kyrano - David Graham
- Lord Worden - Peter Dyneley
- Ocean Pioneer II Captain - John Tate
- Ocean Pioneer II No.2 - David Graham
- Lieutenant Jensen - Matt Zimmerman
- Captain Johnson - Ray Barrett
- 1st Officer Collins - David Graham
- Chauffer Stevens - John Tate
- Ocean Pioneer I Commander - John Tate
- Sir Arthur - Peter Dyneley
- TV Reporter - Ray Barrett
- Scottish Onlooker - John Tate
- Pioneer Base, Port London - Ray Barrett (voice only)
International Rescue Equipment UsedEdit
Non-International Rescue Equipment UsedEdit
- Alan Perry was an uncredited camera operator on this episode.
- This is the only episode in which John goes on a rescue. At the end of the episode, he says that he has been on a "dozen" rescue missions.
- Lord Worden was previously seen as Sir Jeremy Hodge in The Perils Of Penelope, while the mayor (on Penelope's right at the launching of Ocean Pioneer II) was previously seen as Professor Holden in The Mighty Atom. Lord Silton and Lovegrove (both from Vault Of Death), Tidman (from The Man From MI.5) and Bob Williams (from Cry Wolf) are also visible in the crowd*Much of the music from this episode is recycled from the Stingray episode The Big Gun.
- The music played during the launch of Ocean Pioneer II is recycled from the Fireball XL5 episode Flying Zodiac and from the Stingray episode Stand by for Action. It was also re-used later in the Captain Scarlet episode The Launching, during the launching of the ship President Roberts.
- Ironically, Virgil accidentally contributes to Ocean Pioneer II's destruction when one of Thunderbird 2's thrusters collides with the sea tanker's antenna, setting it alight.
- Main article: Danger At Ocean Deep/Goofs
- French: Danger sur les mers
- German: Gefahr aus dem Meer
- Spanish: Alerta en el Fondo del Océano; Peligro en alta mar (DVD)
- Italian: Pericolo in alto mare
- Dutch: De kokende zee (TV); Gevaar in de diepe zee (VHS, DVD)
- Japanese: オーシャンパイオニア号の危機