A smart arse question in our Pub Quiz (UK) was, " To an American serviceman if a P51 wasn’t the Mustang what was it?"
The answer given was that it was a tin-opener. Is this so? And if so was it merely a slang expression or a quartermaster’s inventory reference number?
It allegedly took 51 cuts to make it around a standard sized can. The P-51 (I always heard it called a P-38) is a small hinged metal device, I assume it was service issued.
http://www.campmor.com/webapp/commerce/command/ProductDisplay?prmenbr=226&prrfnbr=13528
The P-51 is a larger version of the P-38 (which is also the number of the Lightning fighter plane, as well as a pistol). Both are extremely simple little can openers which can be carried on a keychain.
The only origin of “P-38” I’ve been able to find is that it’s supposed to take 38 punctures to open a C-ration; I suppose it would take 51 punctures to open the largercamp-size cans with a P-51. It sounds very unlikely to me. I’ve also heard that they were named after the planes, in admiration for the fast attacks by both.
www.dtic.mil/soldiers/august94/p45.html
However, since these numbers are actually used by the Army, I’m sure they were just assigned.
My husband has always called it a P-38. It was included in every box of C-rations, and most GIs put it on their keychain.
These days, with the plastic-bagged MREs, there’s a little cutter to help nick the bags to get them opened.
~VOW
Never heard of a tin-opener called a P51, but I have a P-38 on my keychain. Yes, I have used it – both to open tins, and to perform an emergency field repair on my motorcycle.
I think most American servicemen would say, “A P-51 is the Mustang.”
(IANA serviceman.)
Not this serviceman. I too have a P-38 on my keychain (15 years now) and have found it invaluable. My late father gave me a couple of P-51s (larger version of P-38) that he had scrounged up during his military career. The first I heard of the P-51 Mustang was from the movie Empire of the Sun when the main character shouts at his rescuers “P-51 Mustang! Cadillac of the skies!”
(Service Member since 1985.)
Empire of the Sun? You’re a latecomer! My first model airplane was a P-15 Mustang. I was six. (My first model was the USS Nautilus.) 
A Cadillac with a Rolls Royce engine no less (by way of Packard). Though early P-51As and A-36s had Allison engines which are a little closer to Cadillac’s heritage few saw service and they were not portrayed in the movie.
For many of us “P-51” will have no connotation aside from possibly the finest airplane ever built.
Trivia Q: Name a movie that features a P-51A dressed as a different airplaine. I gave the movie negative stars so count yourself lucky if you missed it.
While it is, indeed, a tin opener, the overwhelming majority of Yanks would have called it a can opener, of course.
I’ve carried a P-38 with my camping gear for years.
Iron Eagle III, standing in for an ME-109.
Re: My field repair.
A few years ago I was riding my Yamaha at about 80mph on the 405 when the engine suddenly quit. No sputtering, no backfiring, no gradual loss of power – it just turned off.
When I got to the right shoulder I quickly diagnosed the problem. My bike has a kickstand interlock that kills the engine if the transmission is taken out of neutral while the kickstand is down. One of the wires had broken. Just that day I had stopped carrying a pocket knife, as I almost never had a use for one. The only “sharp” thing I had was my trusty P-38 can opener. While the point is kind-of sharp, the “blade” is about as sharp as a dull rock. But by picking at the wire with the point and scraping with the edge, I was able to get some bare wire. I twisted the wire around a handy piece of bare metal and was soon on my way. Without my P-38, I would’ve been stuck.
I probably should have disqualified you but give that man a cigar anyway. I got to be an extra in the air show sequence which was shot at Avra Valley Airport where Patty Wagstaff trains. It was much more entertaining than the movie. The mockup Spitfire used in the inverted, falling out of the straps bit sat on the corner of Grant Rd. & Tucson Boulevard for years until it succumbed to vandalism and weather.
I got to be an extra in The Right Stuff, but I didn’t make it into the final cut. 