OK lets hear from a former chow SGT. Any out there?
Heres my understanding and it may be wrong:
Class A rations: made from fresh ingrediants(good luck)
Class B: made from a combination of fresh and canned ingrediants.Most dining facilities use this.

Class C: ration,combat,individual.
K rations were WWII and into Korea.
D Rations-never exposed to them.