The Sea Devils (TV story)

The Sea Devils was the third serial of season 9 of Doctor Who. It marked the first appearance of the Sea Devils and the reappearance of, now plotting to escape confinement from a maximum security prison.

Barry Letts and Terrance Dicks had decided they wanted a sea-based story and asked Malcolm Hulke to write it. Rather than merely bringing back the Silurians, Hulke invented an aquatic version called the Sea Silurians. Unlike their earlier counterparts, these "Sea Devils" were given clothing, designed by Maggie Fletcher.

To answer the insistence by fans that the Silurian era could not have spawned man-sized life, Hulke introduced a line in which the Doctor says they should correctly be called Eocenes. However, this period was still well in advance of humanoid life.

After appeared in all five stories of season 8, Letts decided to restrict him to a few appearances each year. This story joins him where The Dæmons left off, in prison. This is the first mention that he and the Doctor were once friends.

Letts had secured the involvement of the Royal Air Force for The Mind of Evil and decided to try to do the same with the Royal Navy. He found the Ministry of Defence eager to take part. Many of the extras that played the navy personnel were active duty sailors. Shortly after broadcast, the BBC was visited by officials from the MOD who believed a top-secret submarine had been used in the show. It was in fact a model, adapted to show the features they were secretly testing.

Expensive location filming left The Sea Devils with a budgeting problem. Director Michael Briant's solution was to not hire regular incidental music composer, Dudley Simpson, and have the score created by the BBC Radiophonic Workshop. Malcolm Clarke's electronic score was one of the serial's signatures. Its significance was attested to by its inclusion in 2013's Doctor Who at the Proms, where it was one of five pieces of incidental music performed as representative of the show's original run.

This story saw the only use of the catchphrase "reverse the polarity of the neutron flow" during the Pertwee era. The phrase became associated with the Third Doctor, so he used it again in The Five Doctors some eleven years later, although between seasons 7 and 11 Pertwee did use a shortened version of the phrase, "reverse the polarity", several times.

Like many of Hulke's stories, it included a moral dimension. The Sea Devils are caught between the Master, the Doctor and the humans. Ultimately, they are betrayed by all three; like their land-based cousins, it is the humans who hurt them the most.

Synopsis
The Doctor and Jo visit the Master in his high-security prison on an island off the south coast of England. The governor, Colonel Trenchard, says ships have been disappearing mysteriously at sea. The Doctor discovers that Trenchard and the Master are in league to contact the Sea Devils, a race of reptiles in hibernation in a base beneath the sea, who have been awoken by recent work on a nearby sea fort. The Master intends to use his new allies to help him conquer the world.

Episode one
On board the SS Pevensey Castle, a radio operator is sending a mayday call that they are being attacked. Ldg. Telegraphist Bowman receives their transmission from a naval base and asks for their position, but receives static. The radio operator says that they are abandoning ship and is about to give their location when a brown-skinned creature places its hand on the microphone, ending the transmission. The radio operator screams as he is killed.

The Third Doctor and Jo are on a boat approaching a small island. This is Fortress Island, the place where the is being held following his capture. The boat docks and the two disembark. As the Doctor and Jo make their way to a military vehicle, Robbins, the man whose boat they had chartered, says that he'll be back in a couple of hours to return them to the mainland.

When they arrive, George Trenchard, the man running the facility, has them sent to his office. Once Trenchard notices their arrival, they all introduce themselves. Trenchard informs the Doctor and Jo that he was worried that they had sunk, as there have been several ships disappearing recently. Trenchard, to the Doctor's annoyance, asks for their passes, which Jo provides. He asks if they would be seeing the prisoner, which the Doctor confirms. The Doctor asks if the Master has given them any trouble. Trenchard says that he has not, though Jo finds this hard to believe. Trenchard says that they have very strict security precautions and that they're on an island anyway. The Doctor asks if the Master has tried hypnotising the guards, to which Trenchard replies that everyone there is immune to hypnotism. When Jo shows skepticism, Trenchard says he'll prove it to them. He orders that the new guard, Wilson, check in on the Master. He then shows them a video screen showing the Master's cell.

Wilson enters the Master's cell, asking if he needs a new book. The Master says that he's not quite finished with his current one. As Wilson is leaving, the Master asks if he's new at the prison; Wilson replies that he is. The Master then attempts to hypnotise him, seemingly to no effect. Wilson then leaves and Trenchard turns off the monitor. The Doctor says that it is impressive and asks if they could finally see the Master. Trenchard shows them the way to the Master's cell.

They arrive at the Master's cell to see him using a rowing machine. Trenchard informs the Master that he has visitors. After the Master exchanges pleasantries with the Doctor and Jo, Trenchard leaves and tells the Doctor to let the guard know when they want to leave. The Master says that Trenchard is a decent man and that he used to be the leader of a colony. The Doctor says that it was a very small colony and that they'd claimed independence soon after Trenchard arrived. Jo says that the Master seems to be treated well, to which the Master replies that he has everything that he wants aside from his freedom. The Doctor says that he should consider himself lucky, as there were those who wanted him executed. The Master says that he is not ungrateful and that it's given him time to rethink his life choices. The Doctor asks if he's reformed, to which the Master says that he has a lot to repent for. The Doctor says that if he's changed to give him the location of his TARDIS. The Master asks if he wants to know so he can escape Earth. The Doctor says that he simply wants to make sure that the Master can't. The Master says that giving the location of his TARDIS is too much to ask. The Doctor is unsurprised and leaves the cell with Jo. Before leaving, the Doctor asks the Master if there's anything he can do for him. The Master asks that he visit occasionally, saying that Trenchard is nice, but not much good for conversation. They say their goodbyes and the Master offers the Doctor a handshake, but the Doctor decides to wave instead. Once they have left, the Master laughs maniacally.

Jo asks the Doctor if the reason he wanted to see the Master was if he felt sorry for the Master and to see if he was all right. The Doctor says that he and the Master used to be very good friends and that they were even at school together. Jo asks how long the Master is going to be imprisoned for. The Doctor says that he thinks the Master will be held forever. Trenchard comes in to stamp their passes before they leave. The Doctor acts with incredulity that their passes need further marking, but Trenchard says that it's the rules. The Doctor warns Trenchard to be careful of the Master as he's very dangerous, but Trenchard says not to worry as he keeps an eye on him. Trenchard returns their passes to Jo and shows them out.

The Master is in Trenchard's office when he returns, and Trenchard tells him that he thinks they'd fooled them. The Master says that he hopes so and tells Trenchard not to underestimate the Doctor. He then asks Trenchard if he thinks the Doctor really came to see him. Trenchard asks why else he would come. The Master points out the matter of the disappearing ships. When Trenchard says that the Doctor didn't seem interested when he'd brought it up, The Master responds with anger. Trenchard says that he was just chatting and that there as no harm done. The Master says that they should hope not. Before leaving, he asks when he will be receiving the admiralty charts he had asked for. Trenchard says they'll arrive that afternoon. Before returning to his cell, the Master asks for another television for his bedroom, spefically a colour set, which Trenchard agrees to.

Robbins is walking with the Doctor telling him about the missing ships, saying that people from the nearby naval research base were trying to hush it up. When the Doctor asks Robbins how he knows all this, he tells him he's in the lifeboat crew. He says that they only found one lifeboat and that it was charred in a strange pattern. When the Doctor asks what happened to it, Robbins said that the Navy took it and told them not to say anything. The Doctor asks where the naval base is, and Robbins points it out. When the Doctor asks Robbins to take him there, he says that Trenchard only payed him to travel to and from the island and that if the Doctor wants to go to the base he'll need to make his own arrangements. The Doctor bribes Robbins into letting him use his boat. He then sails off as Robbins pockets the money

At the naval base, the HMS Seaspite, John Hart is dictating a message to his secretary, Jane Blythe, about the missing ships, saying that they don't yet know why they sank but will send the scorched lifeboat to their lab. He stops as he notices something out the window and calls his secretary to take a look. Through the window, they see the doctor approaching the base, believing him to be a stray civilian. Hart calls the Master at Arms and instructs him to see to the Doctor. On the beach, the Doctor approaches the scorched lifeboat and begins to inspect it with a magnifying glass. As the base's guards approach the Doctor, he asks to see their commanding officer.

Meanwhile, Jo is handing Robbins some money in exchange for borrowing his motorcycle. Robbins tells her to take care of it, to which Jo tells him that she will and that she'll return it once she's found the Doctor. She puts on the helmet and goggles and drives off.

Back in the Master's cell, a screen turns on showing a television programme of alien mice-like creatures making slide whistle noises, which the Master is enjoying, and even whistling along with the creatures. Trenchard enters asking what the Master is watching. The Master jokes that it seems to be an interesting extra-terrestrial life form. Trenchard informs the Master that it's only a children's puppet programme. The Master feigns realization and puffs at Trenchard's lack of humour as he turns off the television. Trenchard gives the Master the chart he'd asked for and spreads them out on the table. The Master begins plotting points and tells Trenchard that his talents are wasted at the prison and that once their plan succeeds, people will hold him in higher regard. Trenchard asks him what he's doing and the Master says that he'd been plotting the points where the ships sank, in the middle of which is an abandoned sea fort. Trenchard says that it's not abandoned anymore as it's being converted into a sonar testing station and that contractors are working on it.

At the abandoned base, the contractors, Clark and Hickman, are playing poker. Clark wins the hand and offers Hickman the chance to win his money back. Hickman turns down the offer. Clark asks what's wrong with him and he responds that there's something off about the base. Hickman confirms with Clark that they're the only people on the base before saying that he keeps getting the feeling that they're being watched. Just then, a mysterious hand identical to that from the mysterious Pevensy Castle attack comes in through the window.

Back at the Seaspite, Hart is asking the Doctor where his credentials are if he's with UNIT. The Doctor says he never carries credentials as they're bureaucratic nonsense. He says that Jo has his pass and enters Hart's office. Hart asks why he didn't arrange a meeting and the Doctor says that he dropped by on impulse after hearing about the lifeboat. He borrows a pad of paper from Hart's secretary and draws the scorch pattern on the lifeboat, pointing out that it is very linear. Hart attributes this to a freak effect of the ship catching fire. The Doctor points out that it couldn't have caught fire as no one had seen any smoke or flames. The Doctor gives his explanation; a concentrated beam of heat from below the boat while it was in the water. He claims it was done intentionally so that there would be no survivors. He then approaches a map and ask what the markers mean. Hart says that they indicate the last known position of the missing ships. Just then, there's a call saying that a young lady has arrived with two UNIT passes asking after the Doctor.

Back at the abandoned fort, Clark is trying to convince Hickman to play draughts when a noise is heard from upstairs. Hickman loads a flare gun "just in case" and goes to investigate. Clark hears Hickman scream from upstairs and goes in search of him. He finds Hickman lying dead and turns to see a strange, brown creature.

Meanwhile at the Seaspite, Hartman has approved of the Doctor and Jo's passes and tells them that they can leave. The Doctor says that he doesn't want to leave, but visit the sea fort. Hart informs him that it is being converted into a sonar test station and that no one is there but some workmen. The Doctor points out that it is at the centre of the disappearances and asks for some of Hart's men to bring him there. Hart refuses and Jo says that they had best leave. Hart says that he should take things up with UNIT and make it an official matter. As he is leaving, the Doctor says that if Horatio Nelson were in charge he wouldn't have waited for things to be made official. Hart says that Nelson was impulsive, if the history books were to be believed. The Doctor then says that he knew Nelson personally and leaves with Jo. Hart thinks that the Doctor is mad.

The Doctor and Jo make their way to the sea fort on Robbins' boat. Jo says they should have returned the boat. The Doctor says that they will and return the motorcycle at the same time. As they begin searching the fort, the creature's hand reaches over the side of the boat. The Doctor and Jo find the room where Clark and Hickman were playing poker and wonder where they are. As they start looking for them, the boat begins smoking. After not having luck finding the two workmen, Jo says that they should head back as it's getting dark. As the Doctor is saying that there's plenty of time before they need to return, they hear an explosion and rush to a window. At the spot where the boat was moored are now scraps of wreckage. The Doctor and Jo go in search of a radio to contact shore, and are followed by the creature. They find Hickman's body upstairs. Jo pleads the Doctor to leave, to which the Doctor says that they will once they find the radio. Just then, Jo hears something moving towards them...

Episode two
It is the second crewman, Clark, who is now half-mad and ranting about "Sea Devils". The Doctor and Jo try to calm him down. They find that the radio was ripped out. The Doctor decides to go get a transistor radio in order to turn it into a transmitter. On his way, he encounters a hostile reptilian Sea Devil, who fires at him. When it tries to break in, it is injured and flees. Shortly afterwards, the Doctor finishes his transmitter, and they are rescued.

Captain Hart decides to find them after they apparently disappear. The Doctor and Jo attempt to get Hart to tell a higher authority. His assistant gets a call from someone ranting about Sea Devils. The Master comes to HMS Seaspite to steal some equipment, posing as an officer but is caught in the act of robbing the stores by a petty officer but the Master knocks the man unconscious. In the meantime, Colonel Trenchard is providing a distraction by visiting Hart however Jo sees the Master leaving. The alarm is raised but the Master and Trenchard have already escaped.

The Doctor and Jo confront Trenchard, and he tries to dissuade them by showing that the Master is in his cell. The Master knocks out a guard and grabs his knife. Trenchard then gets the Doctor to go and see the Master, who attempts to kill him, first with a gun and then with a sword. The Doctor and the Master engage in a sword fight. The Master then throws a dagger at the back of the Doctor's head....

Episode three
The Master misses, and the Doctor is unharmed. Trenchard enters and decides to lock the Doctor in the prison and attempts to capture Jo. The Master tells him that he intends to use the reptiles as an army to conquer the planet.

It is revealed that the reason Trenchard is helping the Master is because he believes they are fighting enemy agents. Meanwhile, Jo comes and frees the Doctor. The Master and Trenchard give chase, and the Master uses the machine to summon a Sea Devil from the ocean. The Doctor and Jo are trapped between the Sea Devil, the Master, and a minefield.

Episode four
The Doctor is forced to employ his sonic screwdriver to repel the Sea Devils by exploding mines on the beach. While the Doctor and Jo navigate through a mine field, a Sea Devil attacks a submarine Hart arranged to be sent to investigate the sinking of the ships. The Doctor and Jo flee to HMS Seaspite, where Hart tells them another naval submarine has disappeared.

Meanwhile, the Master returns to his cell to begin work on a new device. He activates it, and it calls the Sea Devils to him. They attack the prison, killing the guards. A battle for the prison rages. Trenchard, who believed he was aiding his country against enemy agents, is killed. The Reclaim heads out to investigate a section of seabed. The Doctor goes down in a diving bell. When they offer to pull him up, he refuses; however, his communication system fails, and Captain Hart orders the crew to pull up the diving bell. When it reaches the ship, it is empty...

Episode five
The Sea Devils take the Doctor to their leader. The Doctor enters the Sea Devils' base and tries to encourage peaceful negotiation, recalling how he had failed to broker an agreement between mankind and the Silurians. The Master arrives to incite matters by trying to provoke war.

Walker, the parliamentary private secretary, arrives to "solve" the sinking ship problem by dropping depth charges. Meanwhile, the Doctor has gained the upper side of the argument — the Sea Devils agree to consider diplomatic relations. The depth charges disrupt the negotiations. The Master convinces the Sea Devils to take the Doctor away and kill him. He also convinces them to attack one of the naval bases. In the confusion caused by the depth charges, the Doctor escapes, gets a Silurian gun from a fallen Sea Devil, and uses it to melt a door and rescue two of the submarine crew. They rescue the others still in the submarine. The leader of the submarine crew kills one of the Sea Devils with the gun that the Doctor picked up; it is implied that others were killed on the upper level of the sub. They try to leave, but the Sea Devils hold them back with a force field. They fire torpedoes to provide thrust and escape.

The Doctor confronts Walker about his depth charges, which have just made the Sea Devils angry. The Sea Devils rise and attack the HMS Seaspite. The Doctor attempts to go to negotiate again. As they round a corner, a Sea Devil appears and raises its gun at them...

Episode six
The Doctor fights the Sea Devil off with Venusian karate, but another captures him. The rest of the Sea Devils capture the rest of the people at the base. Jo, Captain Hart, and Walker are held in one of the offices at the base. The Master tells the Doctor that he needs help to complete his machine so he can revive the colonies all over the world.

Meanwhile, Jo escapes through a ventilation shaft. She reaches the Doctor, and he tells her that he will deal with the guards; he sends her back to retrieve Captain Hart and Walker. The Doctor makes the machine emit a shrill noise, which puts the Sea Devils in agony. Captain Hart escapes with Jo, but Walker retreats into the office and shuts himself back in when faced with a Sea Devil, even though the creature is incapacitated by the noise from the machine. The Master shuts off the machine, and the Doctor apologises for the "mistake" that caused the noise. The Sea Devils, the Doctor, and the Master head back to the Sea Devil base.

The prisoners retake the base. A soldier arrives, and the Doctor orders him to keep watch over the Master, but the Master hypnotises him and escapes. The Doctor chases after the Master, and they reach the base, where multiple Sea Devils capture them. Meanwhile, Walker orders a nuclear strike. The Doctor sabotages the machine, and the two Time Lords are imprisoned. The Doctor reveals that he reversed the polarity of neutron flow, which will cause a massive explosion. The Time Lords escape by using the Doctor's sonic screwdriver to get out of their cell; they find diving suits and exit the base. They rise to the surface and are rescued by a Naval hovercraft just before the base explodes, and the Sea Devils are destroyed.

The rescuers have called an ambulance for the Master, who appears to have suffered a heart attack on board the hovercraft. However, when the ambulance arrives, the Doctor and Jo realise the man brought out on the stretcher is not really the Master, but a hovercraft crew member wearing a latex mask — the Master has hypnotised him and forced him to act as a decoy. They realise that the Master has stolen the hovercraft and, too late to do anything to stop him, all they can do is bitterly watch their foe taunt them as he escapes to fight another day.

Cast

 * Doctor Who - Jon Pertwee
 * - Roger Delgado
 * Jo Grant - Katy Manning
 * Captain Hart - Edwin Richfield
 * Trenchard - Clive Morton
 * Robbins - Royston Tickner
 * Radio Operator - Neil Seiler
 * Clark - Declan Mulholland
 * Hickman - Hugh Futcher
 * 3rd Officer Jane Blythe - June Murphy
 * Ldg. Telegraphist Bowman - Alec Wallis
 * Castle Guard Wilson - Brian Justice
 * Castle Guard Barclay - Terry Walsh
 * Sea Devil - Pat Gorman
 * C.P.O. Smedley - Eric Mason
 * Commander Ridgeway - Donald Sumpter
 * Lt. Commander Mitchell - David Griffin
 * Ldg. Seaman Lovell - Christopher Wray
 * Castle Guard Drew - Stanley McGeagh
 * C.P.O. Summers - Colin Bell
 * Lt. Commander Watts - Brian Vaughan
 * A/B Girton - Rex Rowland
 * Walker - Martin Boddey
 * Rear Admiral - Norman Atkyns
 * Chief Sea Devil - Peter Forbes-Robertson
 * C.P.O. Myers - John Caesar

Uncredited cast

 * Castle Guards - Mike Stephens, Marc Boyle, Mike Horsburgh, Peter Brace, Philip Weston, Stewart Barry, Bob Blaine, Brian Gilmar, Jim Dowdall, Les Clark (DWM 192)
 * DJ Voice - Michael Briant (DWM 192)
 * Sea Devils - Stuart Fell, Brian Nolan, Geoff Witherick, Brian Nolan, Steven Ismay, Frank Seton, Terry Walsh, Mike Stephens, Mike Horsburgh, Marc Boyle, Peter Brace (DWM 192)
 * Marines - Derek Ware, Alan Chuntz, Billie Horrigan, Jack Cooper (DWM 192)
 * Sailors - Terry Walsh, Jim Dowdall, Mike Stephens, Stuart Fell, Marc Boyle, Peter Brace, Mike Horsburgh, Dennis Plenty, Roy Pearce, Nick Llewellyn, Ron Tingley (DWM 192)
 * Submarine Crewman - Dennis Plenty, Roy Pearce, Ron Tingley, Nick Llewellyn (DWM 192)

Crew

 * Writer - Malcolm Hulke
 * The BBC wish to acknowledge the help given to them by the Royal Navy in the making of this programme
 * Title Music - Ron Grainer and BBC Radiophonic Workshop
 * Incidental Music - Malcolm Clarke, BBC Radiophonic Workshop
 * Special Sounds - Brian Hodgson
 * Film Cameraman - Peter Sargent
 * Film Editor - Martyn Day
 * Visual Effects - Peter Day
 * Costumes - Maggie Fletcher
 * Make-up - Sylvia James
 * Studio Lighting - Mike Jefferies
 * Sound - Tony Millier, Colin Dixon
 * Script Editor - Terrance Dicks
 * Designer - Tony Snoaden
 * Producer - Barry Letts
 * Director - Michael Briant
 * Action by HAVOC

Uncredited crew

 * Visual Effects Assistant - Len Hutton (INFO: The Sea Devils)
 * Location Bookings Assistant - Jennie Betts (INFO: The Sea Devils)
 * Grams Operators - Gordon Phillipson, Barry Bonner (INFO: The Sea Devils)
 * Film Operations Assistant - PW Walsh (INFO: The Sea Devils)
 * Film Sound Assistant - Alec Christison (INFO: The Sea Devils)
 * Film Camera Assistant - John Jefford (INFO: The Sea Devils)
 * Props - Joe Bates, John Watson (INFO: The Sea Devils)
 * Make-Up Assistant - Joanne Burn (INFO: The Sea Devils)
 * Technical Manager - Peter Valentine (INFO: The Sea Devils)
 * Film Unit Electricians - John Collins, Tony Thorpe (INFO: The Sea Devils)
 * Film Camera Assistants - Ian Punter, Roger Twyman (INFO: The Sea Devils)
 * Costume Assistants - Grace Dawson, Jack Roe (INFO: The Sea Devils)
 * Production Secretary - Sarah Newman (INFO: The Sea Devils)
 * Floor Assistant - Tony Cox (INFO: The Sea Devils)
 * Vision Mixer - John Gorman (INFO: The Sea Devils)
 * Producer's Secretary - Pauline Silcock (INFO: The Sea Devils)
 * Grips - Bill Paget (INFO: The Sea Devils)
 * Armourer - Douglas Needham (INFO: The Sea Devils)
 * Costume Assistant - Barry Simmons (INFO: The Sea Devils)

Cultural references from the real world

 * While imprisoned, the Master watched Clangers.

Continuity

 * was captured at Devil's End.
 * Hart mentions Trinity House marker buoys.

Foods and beverages

 * The Doctor consumes several sandwiches at the naval base.
 * Hickman is seen drinking Old Oak Light Ale.
 * Walker continually asks Officer Blythe to bring him food and tea. He also eats smoked salmon.

Species

 * The Silurians had emerged from some caves in Derbyshire.
 * The Master learned about the Sea Devils from the files he stole from the Time Lords.

The Doctor

 * The Doctor is a trained diver and accomplished golfer.
 * The Doctor remarks he was a personal friend of Horatio Nelson.
 * The Doctor claims he had been wounded at the Crimean War, Gallipoli or El Alamein.

Vehicles

 * The merchant ship SS Pevensey Castle is attacked by the Sea Devils.
 * The Royal Navy drove Land Rover vehicles.

Story notes

 * This story had the working title The Sea Silurians.
 * This is one of two television stories where the Third Doctor utters the full line, "I reversed the polarity of the neutron flow" (in episode six). The other is in The Five Doctors.
 * The scene involving the Master watching The Clangers on television was a last-minute addition, added because episode one was running ninety seconds short.
 * This serial's director, Michael Briant, provided the voice of the radio DJ in episode two.
 * This is the last story to feature the Third Doctor wearing his original outfit in his run. It wasn't seen again until The Day of the Doctor.
 * This is the last story that HAVOC worked on.
 * Originally, episode one was to include the Doctor water-skiing, which was to be used as the excuse for Jo and him being late to the Master's prison. Increasingly inclement weather made the shoot impossible.
 * The Radio Times programme listing for the 90-minute compilation repeat of the story on Wednesday 27 December 1972, billed as Dr. Who and the Sea Devils, was accompanied by a black-and-white illustration by Frank Bellamy depicting a Sea Devil, the Master and the Doctor, along with a comic strip-style caption "THE WHOLE PLACE WILL GO UP IN APPROXIMATELY TEN MINUTES / ENJOY YOUR REVENGE!", with the accompanying caption "Time-warp time — the Doc takes on the Master and the Sea Devils: 3.5". (original published text)  The compilation also received an unscheduled showing at 11:15 a.m. on Monday 27 May 1974 as a replacement for the Yorkshire -v- Lancashire cricket match, the planned coverage of which was disrupted by industrial action. The omnibus edition of The Sea Devils was not retained by the BBC Archives, with the 625 line PAL colour videotape being erased for reuse around late May/early June 1974.
 * Reproductions of actual script pages, accompanied by extensive production notes about this serial, are featured in the book The Making of Doctor Who.
 * This is one of only eleven televised stories in the history of Doctor Who not to feature the TARDIS at all, along with Mission to the Unknown, Doctor Who and the Silurians, The Mind of Evil, The Dæmons, The Sontaran Experiment, Genesis of the Daleks, Midnight, The Lie of the Land, The Woman Who Fell to Earth and Ascension of the Cybermen.
 * After the show aired, MI5 came to the studio asking how they came up with the nuclear submarine model. The director and the visual effects designer explained that they simply used an off-the-shelf model kit, but replaced the propeller with a vacuum cleaner part because the model’s propeller didn’t look seaworthy. By sheer happenstance, the vacuum cleaner part had the exact same number of blades as the real nuclear submarine's propeller, meaning they accidentally guessed classified information that revealed the sonar signal that identified British nuclear submarines.
 * Director Michael E. Briant admitted that Malcolm Clarke's choice of music was a mistake. Clark himself admitted that he never cracked the problem of what Barry Letts liked and if he could have modified the work.
 * During filming, stunt performer Stuart Fell nearly drowned when he fell over in the surf and his rubber monster costume filled with water.
 * The sea fort setting was a late change to the scripts: Malcolm Hulke had originally written this material for an oil rig, but Michael E. Briant was unable to obtain permission to film on one.
 * The Doctor's line about the Silurians actually being called Eocenes was added by Malcolm Hulke after fans pointed out that the Silurian era could not have produced man-sized life.
 * Jon Pertwee injured his ribs during recording when he dived forward and fell on the sonic screwdriver prop, which was stowed in his breast pocket.
 * The script originally had a speedboat chase, but Jon Pertwee suggested jet skis.
 * Nicholas Courtney was on holiday during the making of this story, hence the absence of UNIT and the Brigadier.
 * Michael E. Briant recalled that there was a huge discussion on location about how the Sea Devils couldn't be naked, so costume designer Maggie Fletcher had to rush out and buy five hundred yards of fishing net.
 * The Sea Devils' masks were based on turtles.
 * In episode one, the script called for Jo Grant and the Doctor to climb up a ladder to get into a sea fortress. The ladder proved too slippery for Katy Manning, so stuntman Stuart Fell did the shot dressed as Jo.
 * According to Katy Manning, nearly the entire production came down with seasickness during production - except Jon Pertwee, due to his experience as a sailor.
 * Katy Manning recalled that she and Jon Pertwee did the abseiling stunt themselves, despite her having never done it before. She promptly took the skin off her hands as a result.
 * John Baker was originally meant to score the serial, but, after he fell ill, the duties were instead allocated to Malcolm Clarke.

Ratings

 * Episode one - 6.4 million viewers
 * Episode two - 9.7 million viewers
 * Episode three - 8.3 million viewers
 * Episode four - 7.8 million viewers
 * Episode five - 8.3 million viewers
 * Episode six - 8.5 million viewers

Myths

 * Roger Delgado was afraid of the water, as he couldn't swim, and it took great courage for him to film the scene in which the Master and the Doctor are rescued from the sea by the Navy. (This was frequently recalled by Jon Pertwee in later interviews; but according to Delgado's widow, Kismet, it is untrue: Delgado was actually worried about getting his costume wet, as there was no spare available. Nonetheless, Delgado's fear of water is also recalled during the DVD commentary of The Sea Devils by Barry Letts and Terrance Dicks. Michael Briant also recalls this in the documentary Hello Sailor! Indeed, Delgado looks very uncomfortable during his scenes in the water in the finished programme.)

Filming locations

 * The exterior of the Master's prison was in fact Norris Castle, East Cowes, Isle of Wight.
 * The sea fort is No Man's Land Fort, which is also referred to as No Man's Fort.
 * It is a sea fort in the Solent, near Portsmouth, England.
 * It is one of the Palmerston Forts built between 1867 and 1880 after the recommendations of the 1859 Royal Commission. It is 200 feet in diameter, and lies 1.4 miles off the coast of the Isle of Wight. Built in anticipation of a feared French invasion which never came to pass, it was abandoned at the time of the story's filming.
 * In July 2007, the fort came up for sale after the company owning a proposed hotel idea collapsed and its owner was jailed. In April 2015, the fort finally opened as a hotel, with prices upward of £400 a night.
 * Fraser Gunnery Range, HMS St George, Portsmouth
 * Royal Navy ship HMS Reclaim
 * No Man's Land Sea Fort, Solent
 * Whitecliff Bay, Isle of Wight
 * Bembridge Harbour, Isle of Wight
 * Norris Castle, East Cowes, Isle of Wight
 * Red Cliff, Sandown, Isle of Wight
 * Bembridge Sailing Club, Bembridge, Isle of Wight
 * Priory Bay, Isle of Wight
 * BBC Television Centre (Studio 8), Shepherd's Bush, London
 * The beach in front of the naval base (Fraser Gunnery Range, HMS St George, Portsmouth) is a nudist beach, as are the sand dune parts of Climping Beach in Littlehampton West Sussex, which featured in The Enemy Of The World.

Production errors

 * The clock in the Master's prison cell runs backwards.
 * The Master knocks out a prison guard who enters his cell in episode two. The guard then subsequently disappears - never to be seen again.
 * When the Doctor first takes out the sonic screwdriver in the minefield, a microphone can be seen at the bottom left of the shot.

Continuity

 * The Master was captured in TV: The Dæmons.
 * The Silurians first appeared in TV: Doctor Who and the Silurians.
 * The Fifth Doctor later encounters the Sea Devils and the Silurians together. (TV: Warriors of the Deep)
 * The Eleventh Doctor encountered another variation of Silurians as well. (TV: The Hungry Earth)
 * The Thirteenth Doctor encounters the Sea Devils. (TV: Legend of the Sea Devils)
 * Sea Devils and Silurians appear in PROSE: Blood Heat.
 * The Master watches The Clangers in a fashion similar to his later incarnation watching Teletubbies. (TV: The Sound of Drums)
 * The Doctor attempts to attribute the misnomer "Silurian" to their discoverer. Dr. Quinn had discovered Silurians in the caves in TV: Doctor Who and the Silurians.
 * later mentioned their encounter with the Sea Devils to the Tenth Doctor. (TV: Last of the Time Lords)
 * The Doctor and the Master later engaged in another sword fight on 4 March 1215. (TV: The King's Demons)
 * The Master's escape from custody caused a great scandal in the prison service. (PROSE: Who Killed Kennedy)

Home video and audio releases
Editing for both the VHS and DVD releases was completed by the Doctor Who Restoration Team.

DVD releases
This story was released on DVD as part of the Beneath the Surface collection along with Doctor Who and the Silurians and Warriors of the Deep.

Digital releases
This story is available:
 * for streaming through BritBox (US) as part of Season 9 of Classic Doctor Who.

VHS releases
This story was released on video in episodic format.

Audio releases
A CD of the original television soundtrack was released in January 2008, with linking narration by Katy Manning. It was also included in the Monsters on Earth box set along with Doctor Who and the Silurians and Warriors of the Deep.