I think they rotate when the show gets canceled, which means "Harm" should be getting ready for his "challenging and rewarding" disassociated sea tour about now.
As an aside, both JAG and NCIS occasionally film here at Point Mugu. They drag our jets over and wet the concrete and put up this wooden "Enterprise" superstructure, and voila...insta carrier! They also use our enlisted guys as extras, sort of as an MWR-type good deal thing. NCIS was here two weeks ago--Mark Harmon stood right next to me, but he didn't ask this "real American hero" for an autograph. I didn't ask for his, either, but he is a real nice man. But our secretary keeps giving him our Playboy bunny T-shirts for free. We did sell $400 worth of geedunk to the production crew, though.
Speaking of NCIS, the black Tomcat, Vandy 1, which has had the traditional VX-4/9 Bunny logo back on it for the last year, was in the shot, and they had to put a big black cover on the tail. Good thing, too--we like to keep the Bunny thing kinda quiet, so that all the political point-makers/protestors won't come out of the woodwork. However, NCIS hasn't used the jet with my name on it yet, natch.
And finally, as one of our pilots here at the det said: "Only Hollywood would make a TV series about one of the most incompetent investigative services on Earth."