You may be thinking of Jimi Hendrix or John Fogarty, both of whom served in the Army.
Jim Morrison was never in the military, although his father was a high ranking Navy Officer. Simpsons trivia: in an episode in which Otto the pothead schoolbus driver refers to his estranged father, "the admiral," it's a nod to Jim Morrison.
Morrison was also a Clearwater, FL college roomate of the future Judge Greer (of Schiavo infamy), until Jim left that "$hithole" for L.A., where he attended film school with George Lucas.