Everybody's heard of K-Rations, which fell out of favor and were discontinued around 1948 (and didn't have any Topps Gum). They were replaced by C-Rations and Topps managed to secure a deal with the government sometime around 1949 to include what would have been a penny tab of candy coated ammoniated gum (2 peppermint Chiclets-sized pieces) in the accessory pack.
Derived from the penny tabs of Topps Gum that were the first Topps product, the C-Ration gum packaging looked like this:
Picture the old one-cent piece of Bazooka if you're of a certain age-that's the size of these. The bottom was similar:
Looks at these tasty ingredients, courtesy of the indicia:
Mmmmmm...Carbanbide! You can see how "ammoniated" gum derived it's name from Ammonium Phosphate. That was the big thing after the war actually, although it's hard to believe now.
Here's the 1949 copyright, which I am thinking must have been the date these were introduced into the rations. If not, they were in them by 1951 at the latest:
An alternate version exists as well, it has a slightly different shape.
That one also has a 1949 copyright, according the BFF o'the Archive Jeff Shepherd, who provided that scan.
I believe Topps was able to keep their contract with the government through 1958, although details are pretty scarce. I have yet to find a picture of a full ration kit showing the gum, which may have been wrapped in dark plastic along with some cigarettes and a few other small items. Have a smoke, then pop some Topps Gum for minty fresh breath in your foxhole!
UPDATE: Intrepid reader Scott Boroczky posted a great link in the comments. Check in at the 18:45 mark for Topps Gum content, or watch the whole thing-it's pretty entertaining and the vlogger is nuts! https://www.youtube.com/watch?v=nSIXdNlmuB4