From 1953 to 1955, Leonard Nimoy, the actor who played Spock on the original Star Trek, served in the US Army Reserves. Today, he tweeted this photo of himself with the caption "Mopping up."
Bonus fact: while in the service, Sgt. Nimoy supervised Ken Berry, the comedic actor from F-Troop and Mama's Family.*
*Source: The Sunday Mail (Brisbane). Mar. 23, 2003.