In the previous round of Beggar-my-neighbour-no-make-that-blow-him-to-bits, the pet-name Big Bertha had become popular, applied to various bits of heavy artillery. It strictly applies to one particular howitzer named after the heiress Bertha Krupp (according to various sources, for example Bull and Murphy [now out of print but you can pick up a second-hand copy for a mere 250 smackers!] though this attribution is pooh-poohed by Willy Ley, writing in the Journal of Coastal Artillery, Feb, 1943 (says Wikipedia, and life's too short to chase down killjoys like that - who cast doubt on perfectly plausible bits of etymological trivia).
Big Bertha was one of the kanonen that came out of the Krupp works. One of the earlier bearers of the name, before Krupp's became the largest private company in the German empire, was known as 'the Cannon King'. The image of the cannon had been used centuries earlier by Spanish soldiers (conquistadores, I think, though the dates in The Etymological Dictionary call this into question) used to describe a sort of long straight valley of a kind unknown to them in their homeland. They called it un cañón, borrowed into English as 'canyon' - Spanish ñ being the conventional manuscript abbreviation for an original Latin -NN-. So in English we now have both 'cannon' and 'canyon', both derived from the Latin for 'reed'. So the tradition of giving unthreatening pet-names to weapons had been, in a sense, pre-figured by using a weapon's name to refer to an unthreatening rock-formation.
As early as the fifteenth century the metaphorical tide had changed direction, with Mons Meg. Two centuries later there is said to have been Humpty Dumpty, but the East Anglia Tourist Board appears to have started the hare (I'm afraid that's what it is - and Tourist Boards [and the tourism industry in general] have a lot to answer for when it comes to disseminating dubious folk-etymologies) in 1996. Albert Jack, in Pop Goes the Weasel: The Secret Meanings of Nursery Rhymes, retells the story. In a previous book (The Real Story of Humpty Dumpty, now out of print) he claims to have seen two lost extra verses, which further substantiate the derivation. But the alleged 'lost verses' are not in the style of the ... canonical (sorry) rhyme, as is argued in an article with the unequivocally sceptical title 'Putting the “dump” in Humpty Dumpty' in the BS Historian.
So I started out with one of those 'plausible bits of etymological trivia' I mentioned earlier, but now have my doubts. It was an interesting journey though, and the use of pet-names for weapons of war is beyond dispute.
Update, 25 November 2021: PS I've just thought of another word derived from Latin CANNA [='reed']. This is not world-shattering news; I'm sure the Indo-European word bank is full of them. But this particular one offers a pleasing contrast to the noise of cannon: it is the French for fishing-rod, canne à pêche (this, incidentally is the first time I've linked to a foreign-language web-site - not very helpfully I imagine, and some of my readers may not speak French - but I couldn't resist the opportunity).
Update 2016.08..08.12:55 – Added footnote
* This joke is almost certainly anachronistic. Little Boy was dropped in early August 1945. As Wikipedia says, in its article on Raphael Lemkin:
The Convention on the Prevention and Punishment of the Crime of Genocide was formally presented and adopted on December 9, 1948.
|Bilingual plaque in memory|
of Rafael Lemkin
So, if the word genocidal had been available for the naming of Little Boy, it would have been a pretty close-run thing.