" The MRE was adopted as the Department of Defense combat ration in 1975. A large-scale production test began in 1978 with delivery in 1981. MRE I (1981) was the first date of pack.
In 1983, a field evaluation was conducted with the 25th Infantry Division for 34 days. They ate noting but MREs three times a day. Although troops rated the ration as acceptable, consumption was low – only about 60% of the calories provided were consumed.
Another test in 1986 with the same division resulted in increased consumption and acceptance.
Based on these tests, a significant number of changes were made to MREs starting with the 1988 MREs (MRE XVIII). 9 of the 12 entrees were replaced with new ones and the entree size was changed from 5oz. to 8oz. Commercial candies were added to 4 menus, hot sauce was added to 4 menus, and cold beverage bases were added to all 12 menus.
After further field testing and as a result of early feedback from Operation Desert Storm, even more changes were made starting with MRE X: commercial freeze-dried coffee replaced the old mil-spec spray-dried coffee, hot sauce was added to all 12 menus, wet pack fruit replaced dehydrated fruits, and commercial candy was included in 4 more menus (for a total of 8).
During Operation Desert Storm, MREs were eaten by troops for far longer than they were originally intended. Originally intended for 10 days or less, many troops ate them for 60+ days. As a result, three changes were quickly made to supplement the MREs and enhance their acceptability: shelf-stable bread in an MRE pouch was developed, a high-heat-stable chocolate bar was developed that wouldn’t melt in the desert heat (this had been attempted before but the bar had a waxy taste and wasn’t widely accepted), and flameless ration heaters were developed as a quick and easy method for troops to heat their entrees."