From last year, former adman Donald P. Bellisario talks about his successes portraying the U.S. Military on the small screen. He himself served in the U.S. Marines during the peacetime 1950s--and came close to punching out the lights of one Lee Harvey Oswald, when he encountered him reading Pravda on a Marine base in California in 1958--but, that's another story (that can be accessed at the TV Legends website).
Bellisario decided to get out of the advertising business after almost two decades, and gamble on a Hollywood career. Fortunately, with his money running low, he met with Stephen Cannell who liked a script he'd submitted for the program Baa Baa Blacksheep, about the exploits of WWII fighter Ace Greg 'Pappy' Boyington.
Bellisario was responsible for Magnum PI (the first Vietnam Veteran portrayed in a heroic light over his military experience), JAG, Quantum Leap, NCIS and Airwolf among others.