Cockpit: This has its origins in early sea warfare. One of the early defensive measures designed into combat ships was an armor lined well (or pit) for the coxswain to drop into when the ammo started flying. Loss of the coxswain meant loss of the ship’s maneuverability.

“Balls to the wall:” In the reciprocating engine days, each engine had three controls - the propeller pitch, the fuel/air mixture and the throttles, whose levers typically had ball shaped knobs on the tops of them. Maximum power was achieved by pushing the throttles as far towards the firewall (right behind the instrument panel) as possible.

The two I have heard are that it takes nine yards of wool to make a proper kilt (I really like that one), and supposedly the WWII bomber machine gun ammo belts were 9 yards long. When you really wanted to go after the enemy (when would you not?) you would give him the whole nine yards.

I’ve heard several other origins, all of which I’ve forgotten.

Back in the days before cement ready mix trucks had additional tag axles added, a typical ready mix truck with tandem duals could physically haul nine cubic yards of ready mix, but couldn’t legally carry that much because one or more axles would be over weight, they would carry about seven or seven and a half cubic yards to be legal.

At the end of the day, if seven yards would not be enough to finish the job, but nine yards would be enough, the driver might be instructed to make the next trip “ the whole nine yards”. This would risk being stopped for over weight, but would save a trip.

That’s one of the versions I heard but forgot. It might just make the most sense.