The Wikipedia article "Smoking in the United States Military" is a very interesting and informative discussion of this topic:https://en.wikipedia.org/wiki/smoking_in_the_united_states_military
Highlights from it:
"Although the military has attempted to implement tobacco control initiatives, the association between smoking and military personnel has persisted to the present day as smoking rates remain high."
Beginning in World War I, tobacco companies began targeting U.S. military personnel, promoting tobacco use as "... psychologically (an) escape from their current circumstances, boosting overall troop morale," and even as the "... last and only solace of the wounded."
Continuing into modern times "... It was commonplace for a drill sergeant to say "smoke ’em if you got ’em, do pushups if you don’t". Non-smoking soldiers would quickly "bum" a cigarette from a friend and they too would soon be smokers. Despite mounting evidence in the 1950s of the adverse health effects of smoking and tobacco use, the military continued to include cigarettes in rations until 1975."
"In 1975, the United States Department of Defense discontinued the inclusion of cigarettes in K-rations and C-rations."
The article goes on to describe the "war" (appropriate term for it) that resulted after 1975 as the government began efforts to discontinue tobacco use among servicemen, especially as the health dangers of tobacco use began to be publicized, and the corresponding efforts of the tobacco industry to oppose this action. It's interesting reading indeed.
The situation today? The military still tolerates smoking among the troops, but continues to have a policy of active discouragement, and smoking restrictions in the armed services are now paralleling those in civilian life.