I don’t have time to back myself up with a cite, but I’m pretty sure it’s “Naval Construction Contract.”
That’s what I get for showing up to this thread late … I was going to post something along those lines.
The only thing I can add now: Vulcan Boobies! Vulcan Boobies! Vulcan Boobies!
I agree. That fact is in either David Gerrold’s “World of Star Trek”, or “The Making of Star Trek” by Roddenberry (With someone else whose name eludes me).
The original Enterprise “blue prints” released in 1975 use Naval Construction Contract 1701. Flashes of the deck plans appeared on a bridge viewscreen in TWOK, so can we consider it canon?
And not, we all fervently pray, Nimoy’s.
Or Kirstie Alley’s, now that I think about it.
Naval Construction Code is correct. It’s been a while since I’ve studied Trek ferverently and minutiae like that is one of the first things to go. 
It’s still not canon though.
CONTRACT, damn it. Ugh.