Last month Language Log spread the word that the phrase "the whole nine yards" can now be dated as early as...1964. Yes, I can now be confident that it's older than I am.
There have been many explanations of the origin of that phrase, most of them involving long-ago or not-quite-so-long-ago-but-still-quaint technology. As Michael Quinion wrote at World Wide Words:
I’ve seen references to the size of a nun’s habit, the amount of material needed to make a man’s three-piece suit, the length of a maharajah’s ceremonial sash, the capacity of a West Virginia ore wagon, the volume of rubbish that would fill a standard garbage truck, the length of a hangman’s noose, how far you would have to sprint during a jail break to get from the cellblock to the outer wall, the length of a standard bolt of cloth, the volume of a rich man’s grave, or just possibly the length of his shroud, the size of a soldier’s pack, the length of cloth needed for a Scottish “great kilt”, or some distance associated with sports or athletics, especially the game of American football.But none of those theories hold water, especially when we consider the relative youth of the expression.
A couple of the theories Quinion chronicled involve American military aviators, which connects with the 1964 translation that Language Log quoted. So I'm leaning toward .50-calibre machine-gun ammunition belts as the source.