Gents,
While a huge rogue wave is undoubtedly cool, it would still leave some debris and a larger ship would have a larger chance of doing so.
For outright, "vanished from the face of the Earth", X-Files spookiness, which also doesn't rope in little green men, my vote is for a methane upwelling.
Having the sea around Titanic suddenly and dramatically drop in density as a massive amount of methane fizzes into the atmosphere, would result in the liner sinking like the proverbial rock. To an observer, it would seem as if the great ship was literally sucked beneath the waves...
In a methane upwelling, any debris torn from the ship would sink too. The event literally tidies up after itself.
Imagine a different April 14th, 1912...
(Snip)
Holy. Living. F**k.
Jesus H. Christ in a chicken basket, that is excellent! This sort of freakout-inducing event with the Californian as an eyewitness is actually better than what I was going for. Gods, imagine the headlines - they'll likely just consist of "WTF?!" in big block letters! What will this do to the shipping industry?! There may be strenuous efforts by some to try and blame the event on faulty construction somehow while others will focus on finding another cause. I expect the passenger liner industry will take a beating for awhile, but only for awhile - after all, how else could you get across the ocean back then?
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