German or American Military Rations

Can anyone shed light on the 'design' of German or American military ration systems during WW2?

For example, canned rations and candy bars in the US army could be eaten by the man in the most forward foxhole, while there were certainly meals and kitchen equipment ensembles that were designed to be served near the front line or well to the rear (what were these criteria for nearness to the front by ration system?) What does the 'C' in 'C-rations' stand for? What other letter categories of rations did the US use?

I know little about German ration systems, except that regiment-sized units had 'bakery' and 'butcher' detachments, and that a horse-towed field kitchen called a 'Goulaschkanone' or goulash cannon was used. Presumably goulash was served! My overall impression is that the Germans avoided resource-intensive canning and relied heavily on bread baked near the front line and on long shelf-life sausage, as well as stews and soups served up by the goulashkanone. Did the Germans have the equivalent of canned ready-to-eat rations?

Where did soldiers get there vitamin C and (if levity can be pardoned) beta carotene?

How long was one supposed to be able to subsist on each ration system? For example, were you supposed to be able to live, from a nutritional standpoint only, on ready-to-eat rations indefinitely, disregarding the issue of palatability?

Somebody asked:

The US had rations in the Field ration category called A, B, C, and K. It is not clear that the letters actually stood for anything (I think not).

I can photocopy my source (several pages from the _Army Almanac_ [GPO, 1950]) and send it to you by snailmail in preference to typing all of it in. Contact me privately if you want it.

Ed Frank