Lots of.
Top of my head instances:
If you want to considerate him a celebrity or not is another thing, but George Bush Sr. flew Avengers during WW2.
John F. Kennedy was an officer aboard US PT Boats. His boat was sunk when rammed by a japanese destroyer during Guadalcanal, he survived almost by miracle (and because an immense show of fortitude). Probably his back pains who martyrized him later came from that event.
Jimmy Stewart was a Colonel in the 8th USAAF, and an active B-24 pilot who did his good deal of combat missions over germany. He finished the war as General in the USAAF.
Charles Bronson was a gunner aboard B-29s. He got the purple heart over Japan.
Lee Marvin was a marine. He served at Kwajalein and Saipan, and got the purple heart aswell in the latter.
Charlton Heston was a radioman aboard B-25s in the North Pacific area (I think he was serving out of Dutch Harbor)
Mel Brooks was a combat engineer in the US Army.
David Niven served in the British Army as a colonel.
Peter Ustinov was a private in the British Army. And he got to be good friends with Niven at that time. Later they were together in quite some films.
Alec Guinness (Obi-wan Kenobi, rofl
) served in the Royal Navy. He took part in the D-day landings
James Doohan (Scotty in the original Star Trek) was severely wounded at Juno, during D-day. He lost his finger there due to a bullet (he got hit by five more...surprising he survived)
George C. Scott (who later played Patton) was in the USMC.
Douglas Fairbanks, even while american, served in the British Special Forces
John Ford took part in the D-day landings (not as a grunt, he was head of one of the OSS departments, dont' recall which one, but still he was there)
Paul Newman flew in US Navy torpedo bombers (as a gunner ,IIRC)
Tony Curtiss was in the US Navy at the time, serving aboard USS Missouri (he was on board when the Japanese surrendered to McArthur)
Glenn Ford was in the Marines. Dunno if he saw any combat, tho.
Henry Fonda enroled himself in the US Navy after Pearl Harbor. He served on a destroyer in the Pacific.
Kirk Douglas served in the navy aswell, crewman aboard an ASW escort. he even got badly injured once (and I think he even got discharged after that).
And then of course, Audie Murphy, the most condecorated man in WW2. He got to be a quite well known actor (if not star) later in Westerns.
And a funny one: Clark Gable served as a gunner in the 8th Air Force. Hitler knew about this and put a bounty on him if captured alive (he was his favorite actor)
There were plenty more around, some saw combat, some not, but those are the ones I do recall right now.
