Da' Day!

On this day in 1944, the First Special Service Force spent their first full day enjoying the fruits of their recent labors, the newly liberated city of Rome.
Oh, and up to the north, there was something big happened that same day...lots of boats and stuff.
D Day. Another generic term ruined through over-usage... along with "ground-zero". These things used to mean something.
Anyway, sixty-four years ago today, the largest invasion in history took place. Everyone knows that so I won't elaborate other than to say:
D Day alone is enough to ensconce Eisenhower in the pantheon of brilliant generalship.
The simple logistics and coordination necessary to pull this off were impressive.
Like pudgy, old Norm Swartzkopf in "Debacle in Iraqle part 1", he pulled off a staggering feat of administration and management.
And Ike, having been MacArthur's aide during the first war, got to fire his former boss 35 years later.
Sweet.
Anyway, even though the guys on Omaha beach and other places didn't realize it at the time - being preoccupied with staying alive - this was a management miracle.
So, having front-loaded ya'll sufficiently, I'll pose a trivia question:

A tool developed during the depression and first used on a large scale in the construction of the Hoover Dam, enjoyed its first military usage on D Day.
What was said tool?

The answer will be revealed here, 48 hours hence. It'd be longer but my Mom's coming to visit.
Anyway, say 6:30 PM, Sunday the 8th.
The one to guess (or know it already) first... free knuckleduster.
Just post it as a comment. I've disabled all the "don't send me spam" shit so just jump on in.