Answer: None. He was a Secretary of the Navy at one point, but that's a civilian position. He never served in the military but was a very good wartime president.

Many American presidents had no military experience. Some, like Woodrow Wilson, were presidents during major wars. Some were better wartime presidents than others, but military experience isn't a prereq for the office or Clinton could never have been elected.

Other presidents did have military experience but weren't necessarily good for the office, such as U. S. Grant. LBJ did leave his Congressional seat to serve in the Navy during WWII, but the closest he ever came to combat was taking a noncombat flight in a B-17. For that, he got a medal.

Even though I disagree with just about everything he ever did politically, I do give George McGovern a great deal of respect for this service during WWII. He was a B-24 pilot in Italy, which was very dangerous duty. I read about his experiences in The Wild Blue: The Men and Boys Who Flew B-24s over Germany 1944-45 by Stephen Ambrose. It's a good book.