Editor's note: Before you read the posting below, check this page on 'The origin of the whole nine yards'.
Four of my Uncles were in the Airforce during WWII. One of them knew of the phrase during the war. The others either couldn't say if they had heard of it during the war, or when they first heard it.
The Whole Nine Yards was based on the length of the fighter's machine gun belt. If it took every bullet the fighter had to shoot down his foe, "It took the Whole nine yards"