1 Adam: There's a myth that putting a steam engine in a submarine is a stupid thing to do.
2 Adam: In World War One, Britain's Royal Navy commissioned the steam powered K-class submarines.
3 Adam: 17 were built, of which 12 suffered various accidents, collisions, sinkings, and "uncontrolled descents". One even sank while docked.
4 Jamie: Myth confirmed, then?
4 Adam: You'd think so...

This is all true. The British K-class submarines were designed in 1913, and the Royal Navy ordered 21 of the vessels in August 1915.

The first one completed, HMS K3, was delivered in 1916. Just a few months later, the proud Navy was showing off the submarine to 21-year-old Prince Albert, second in line to the British throne. While he was aboard, the ship uncontrollably tipped nose down and mired in the sea floor 50 metres below, where it got stuck in the mud, with the stern portion and propellers of the 103-metre long vessel sticking up out of the water. It required 20 minutes of frantic operations to free it.^[1]

You can read about the litany of other disasters that befell this ship and her sisters at the first Wikipedia link above. The best bit is this quotation, from Admiral John "Jacky" Fisher. When it was first proposed to build the subs in 1913, he had strongly opposed the idea, saying: "The most fatal error imaginable would be to put steam engines in submarines."

He may have been a good Admiral, but he was no Mythbuster.

[1] Surviving this experience, Albert would later go on to succeed to the throne after his older brother Edward abdicated to marry the divorcée Wallis Simpson. Albert adopted the regnal name George VI, and was the father of Queen Elizabeth II. He was also the subject of the film The King's Speech. If that steam powered submarine had perhaps been just a teensy bit more dangerous, history could have turned out rather differently.