" The whole nine yards " .
This expression is from World War 2 and it refers to the length of the M2 .50 caliber machine gun ammunition belt
Not so.
"The Oxford English Dictionary places the earliest published non-idiomatic use of the phrase in the New Albany (Indiana) Daily Ledger, January 30, 1855 in an article called "The Judge's Big Shirt." “What a silly, stupid woman! I told her to get just enough to make three shirts; instead of making three, she has put the whole nine yards into one shirt!” The first known use of the phrase as an idiom appears in The Mitchell Commercial, a newspaper in the small town of Mitchell, Indiana, in its May 2, 1907 edition:
This afternoon at 2:30 will be called one of the baseball games that will be worth going a long way to see. The regular nine is going to play the business men as many innings as they can stand, but we can not promise the full nine yards.
The idiom was used three more times in the Mitchell Commercial over the next seven years, in the forms give him the whole nine yards (i.e., tell someone a big story), take the whole nine yards (i.e., take everything), and settled the whole nine yards (i.e., resolved everything)."
I looked it up and you are right.
The fact that the ammo belt carried on the aircraft was nine yards long is coincidental which is why many are mistaken of the source. I " learned " it while in the Navy and it was taken as fact. But in my defense it seems that the original source was a mainly regional, not national, term which WW2 propagated and because the GIs learned the term in the service, the legend stuck.
" Heard it on the grapevine " Term from the California gold rush.