There are two things that I have noticed about the use of swear words by military and civilians. First, the younger the speaker the more prevalent the use of socially unacceptable language. Second, the people using a large number of swear words seem to be those who are trying to impress the people around them.
Instead of youth, it seems to be tied to education (lower ranking enlisted men/women swear more--especially to impress those in a similar situation) and officers strive to promote a sense of professionalism (they'll swear, but rarely, and only when they think it'll be acceptable--like screaming at an underling or among friend relating their experiences).
P.S. As the son of an officer, I ran into both over the years.
You might think the Marines are a Branch, but they are part of the Department of the Navy.
The marines are the 'infantry of the sea', and were traditionally launched via ships to fight on shore, so they were part of the Navy. They don't use Army gear or support (planes, helicopters, etc.). A few 'specialist fields' work underwater, planting mines/bombs, etc.
My brother-in-law was a career Coast Guardsman.
Actually, there are five branches of the US military
The Coast guard used to be under the department of defense, but now they're under homeland security (there was a period where they were under the finance department (since they run drug interdictions).
Richard, the coast guard frequently have gun battles on the open sea with drug runners and criminal organizations, and yes, they often use a variety of weapons including machine guns.
P.P.S. As a Navy Chaplain, my father was often stationed at Marine bases, and served in Viet Nam with the Marines, instead of the Navy (Marine work on land for the Navy, while the Navy work at sea).