"Pilots, Man Your Planes!"   
                                         WWII U.S. Naval Aviation Collector's Guide                                                                              
U.S. Navy A-14 Oxygen Masks
There appears to have been four Navy contracts for the A-14 oxygen masks. The Ohio Chemical & Mfg. Co. had two plants, one in Cleveland and the other in Minneapolis, Minn.
Contracts from Cleveland, Ohio:
NOa(s)-2264  from 12/43-11/44
N288s-27853  from 12/44-7/45
Contracts from Minneapolis, Minn.:
N288s-23393  from 5/44-12/44
N288s-23843  from 6/44-3/45

Our thanks to Dustin Clingenpeel for his research and providing us with this most helpful information!
The third, and final, step is our attempt to help you “see the forest for the trees.”  As previously mentioned, A-14 masks are still frequently available. The problem is how do you distinguish a Navy mask when you see one? In almost all cases, the actual molded-in markings on the body of the mask itself will say “ Property Air Force, U.S. Army” on the left side regardless of it being procured by the Army or the Navy, so this is of no help. The first thing to look for then, is whether or not an ANB-M-C1 oxygen mask microphone has been installed. If so, it is a most important clue. Fortunately for us, the Navy contract microphones have a shorter cord than those used by the Army Air Force. This, we believe, was due to the Navy’s use of the AN-CX-41/AR5 microphone extension cord, which connected the mask microphone to the radio jack box and included a “push to talk” switch as well as a built in “ring holder”. The presence of a short cord means you’ve found a Navy used mask. If no microphone was ever installed, another clue would be the presence of a “rigger made” mask suspension strap in place of the issue green web adjustment straps.  A third possibility, although much harder to find, would be a mask that has been fitted with the male portion of a hose quick disconnect coupling of the brass Rego #4388 type. Our example has been fitted to the hose end with wire and wrapped with black electrical tape. These fittings would only have been found on very early issue Navy masks, so they don’t turn up too often. Even if none of the above features can be found on the mask you are examining, or you are looking at a mask that was never issued, hope for a successful identification still remains if the mask comes with its’ original box. Visually, the box for a Navy mask is no different than that of an Army issue one. Both are made of the same green cardboard and have the same illustrations on the outside. The key is in the white paper label on the top flap of the box. This will show the manufacturer’s contract number which, for the Navy, will begin with either an N288s or NOa(s) prefix. That’s four possible ways we have to identify a Navy mask. Combine all four and you would have the ultimate example of the Navy A-14!