The Aquadynamics Of Century 21 Submarines: an article by: GF Willmetts.

Looking at a photo of Stingray recently, I went into analytical mode as to its shape before considering Thunderbird 4 and SHADO’s Skydiver. They all share one designer in Derek Meddings so we would expect some similarities. In that respect we would have a dynamic vehicle that can be clearly seen, hence the bright colouring on at least two of them and be instantly recognisable for all three. Both Stingray and Thunderbird 4 have zero ballast when on the surface allowing them to be instantly recognisable.

Had they been based on a comparable traditional submarine, two thirds of their bodies would be underwater which would likely be a problem for moving the models around. As Meddings himself notes, you can’t miniaturise water. Unlike the other three Thunderbirds, doing this with wires would be problematic. The majority of underwater scenes were filmed through a thin double sheet of glass filled with water and fish making it a lot easier to string both vehicles and other underwater craft.


Back in the 1960s, both in the TV Century 21 comic and especially the respected annuals, we were shown schematics, albeit classified of their interiors. More annoyingly, the size of their ballast tanks let alone whether each had a double hull wasn’t clearly shown. Certainly, neither is indicated with Thunderbird 4 and smaller tanks along the sides of Stingray. It has been shown the living section also cannot be a double-hull based on the times it has leaked. Of course, back in the 1960s, nuclear submarines were still highly classified and it might have been difficult to predict what a future submarine would look like. Equally, one could also counter that neither the Terror Fish nor X-20’s submarine would require ballast as their natural environment was underwater. Even so, for them to rise to any particular height they would need to empty their version of ballast tanks. We don’t really see how deep Thunderbird 4 dived to see if it was an advantage for Gordon Tracy.

Despite the few submarine based films before and around this time, giving both submarines glass to look out into the ocean or sea forgets the problem of visibility underwater. Even the American TV series ‘Voyage To The Bottom OF The Sea’s USN Seaview and the Disney film ’20, 000 Leagues Under The Sea’s Nautilus saw no problem with this as there is a desire to give the crew something to see, totally forgetting the depths they dived to would have limited visibility, even with the supplied lights. The Seaquest DSV did actually obey some of these rules for visibility but just looked plain murky and really too large to be viable.

Stingray’s two pilot crew does seem a bit redundant as you would think it only needed one pilot, allowing Lieutenant George ‘Phones’ Sheridan to do his primary job of identifying sonar beeps. Considering the auto-bosun can function for both of them on long voyages. It has also been shown that Captain Troy Tempest could pilot Stingray alone. One would have to assume that the duel piloting was for dramatic effect but would run into problems had either of them did not synchronise their movements. Certainly it would have made more sense for one to steer and the other to monitor speed and targets.

The SHADO submarine Skydiver has to be dealt with separately (sic). Essentially, Diver is the launching platform for the Sky jet-plane for rapid response to alien UFO intrusions where the majority enter over the sea than land. Considering the accuracy of the land radar’s improvement over the years, it seems a logical choice. As was discovered later, staying underwater preserved their hulls from exploding. The consideration for how these UFOs remained underwater without some form of ballast is outside of this remit and the aliens not allowing an examination of their vessels.

The function of Skydiver runs more like a conventional submarine, dependent on sonar navigation, although it does have cameras to view outside when required. The ballast situation is somewhat different. Not only does it have to stay underwater, but to move the ballast to allow an angle greater than 10 degrees to launch the Sky jet. As such, it has two types of ballast with a tank system below the submarine and this one used for rotation. By pumping air into the bottom ballast, Skydiver is able to rise and surf above the waves in a role called ‘sea-skim’ and actually travels faster than underwater.

Deflating this tank enables Skydiver to sink very quickly. Considering that its other prime use is to launch the Sky jet-plane, this bottom tank is likely to be sectioned allowing the front to rise and would explain how it could empty so quickly. Under ‘sub-smash’ conditions, releasing Diver from the ledge it was on allowed its bottom ballast tank to empty and rise to the surface. An effective system for this type of submarine but it is also at least a third smaller than the traditional nuclear submarine and even smaller without the Sky jet plane attached. It should be pointed out that its primary purpose is not to stay underwater indefinitely but more of a transport vehicle for its jet-plane.

Looking at the overall design of Skydiver, it does share a trend since Fireball XL-5 and Zero-X in being able to divide a mobile unit from the main body. Unlike these spacecraft, this was based on an underwater fast response vehicle. It’s a shame we never see both vehicles dock to know whether this was done on the surface or underwater. One would think docking on the surface would be easier than manoeuvring in fathoms of water. Likewise we are also not shown how much fuel Diver carries to fuel the Sky jet-plane but one would think at least two launches, subject to how far it travels.

It is known the Skydiver receives a weekly fuelling stop at sea but this would have to change after Sky jet-plane launches. It is also unlikely that there would be more than one UFO incursion a week or at least certainly enough time between each attack to refuel. It should be pointed out that although Skydiver has a nuclear reactor this alone is not enough to propel it.

Certainly Derek Meddings approach to Skydiver’s design was improved upon compared to Stingray and Thunderbird 4. Preliminary sketches do suggest Meddings wanted to make Skydiver smaller and with few crew although this was changed to allow for a proper 6 crew. The design included here was obviously enlarged for the final TV version although we never see anything beyond the control bridge and the captain’s cabin, although the motors are accessible.

Certainly as submarines, they have never been copied or, in the case of Thunderbird 4 CGI version, only modified for improved accessibility. If I had to improve TB4, I think I would have built a sledge unit to improve its range when Thunderbird 2 was not available.

© GF Willmetts 2022

Ack before borrowing

I like to know where it ends up.


Geoff Willmetts has been editor at SFCrowsnest for some 21 plus years now, showing a versatility and knowledge in not only Science Fiction, but also the sciences and arts, all of which has been displayed here through editorials, reviews, articles and stories. With the latter, he has been running a short story series under the title of ‘Psi-Kicks’ If you want to contribute to SFCrowsnest, read the guidelines and show him what you can do. If it isn’t usable, he spends as much time telling you what the problems is as he would with material he accepts. This is largely how he got called an Uncle, as in Dutch Uncle. He’s not actually Dutch but hails from the west country in the UK.

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