(written from a Production point of view)
Newell Tarrant (born Yancey Newell Tarrant) is a retired Navy flight officer who played Commander Rogerson, the command duty officer of the USS Enterprise in Star Trek IV: The Voyage Home. He is the son of actor Newell Tarrant (1911-2000).
A graduate of the Naval War College and TOPGUN, Tarrant fought over two hundred combat missions in the Vietnam War. He concluded his twenty-year naval career - which included postings on both the Enterprise and the USS Ranger (where scenes aboard the "Enterprise" were actually filmed) - as the commanding officer of the Chargers of VF-161, a carrier-based fighter squadron. Currently residing in San Diego, California, he has become an author, with his first novel, Shadow War, published in 2002. 
Of all the Star Trek personalities with military service, Tarrant is the only one with service in the Vietnam War. During this period, Tarrant was a Navy fighter pilot and was awarded the Distinguished Flying Cross as well as multiple Air Medals. (Source: Navy Personnel Command)