Caruso had a small role in an Officer and a Gentleman, he was one of the guys training to be a naval aviator along with Richard Gere .
Penny Marshall and Mary Kay Place appeared in two or three episodes in the next-to-last season of Mary Tyler Moore as roommate neighbors at Mary’s new apartment building. Penny Marshall looks as if she might’ve been an intended Rhoda substitute, but then she got a better opportunity to lead her own show with Laverne & Shirley.
I’m a bit confused by the OP and the responses. Are we talking about TV stars who had bit parts on the same TV program that they’re known for, but as a different character? Or are we discussing big-name actors who had bit parts on TV shows before going on to bigger and better things?
For an actor that had a bit part before going on to bigger and better things, Jack Black was in an episode of Northern Exposure in the early 90’s playing a high school senior. While he had quite a bit of screen time in that episode it was years before he had a breakout on the big screen. I’m sure there’s a zillion other examples.
For actors that had a small bit part in a series before becoming big names in a different series, also from Northern Exposure (I’m a fan, ok?): Patrick Warburton of Seinfeld and Family Guy fame had a small part in one episode, one of his first acting roles.
For actors that had a small part in a series and then returned to the same series as another character, Debbe Dunning played a one-off character in Home Improvement before returning two years later as a completely different character, which she played for the remainder of the series.
I already mentioned some of the franchise regulars who appeared as one-off characters before they became regulars, but I’m amazed at the sheer number of actors who have played multiple guest roles. I’ll be watching an episode and think I recognize someone so I look them up on IMDb. Seems like at least half the time I recognize them from a different episode of Law & Order. Just yesterday I saw the one where a star baseball player killed his limo driver. I knew I’d seen his lawyer somewhere before. Turns out he was also the control-freak father who pushed a woman in front of a subway train 4 seasons earlier.
In the “major roles in British cult favorites turned into minor roles on US shows that surprised me” category:
Lucy Davis (Dawn from The Office [UK]) playing a random member of the writer’s room on Studio 60 on the Sunset Strip
Chris O’Dowd (Roy from The IT Crowd) playing a weirdo in a few episodes of *Girls *
In the “minor role(s) on one show before getting a major role on that same show” category:
Jon Lovitz had two one-episode stints on NewsRadio (one was where he was a guy threatening to jump off their building; I don’t remember the other one) before “replacing” Phil Hartman in the final season.
He was also hilarious as an arrogant DEA agent in Con Air.
Darren Boyd from Kiss Me Kate became a regular on the Julia Louis Dreyfus vehicle Watching Ellie. Kiss Me Kate was also the first thing I ever saw Bill Nighy in, but he seems to be everywhere the last few years.
Gina Bellman was Jane on the original UK version of Coupling, then played Sophie for five years on Leverage.
Armin Shimerman (who played Quark in Star Trek: Deep Space Nine) played a doctor in the Jean Claude van Damme film Death Warrant.
Jerry Orbach played a cop in the Steven Seagal film Out for Justice and a doctor in the Jean Claude van Damme film Universal Soldier.
Speaking of van Damme films, Forest Whitaker played a small role in Bloodsport, Ted Levine (the captain from Monk) was in Nowhere to Run, and Jaime Pressly(from My Name is Earl) was in Inferno aka Desert Heat.
Jill Hennessy(from Law & Order) was in Robocop III.
Also it’s not a minor role, but Rob Schneider co-starred with Jean Claude van Damme in* Knock-Off*.
How on earth did they explain the ears?
also played a Dr. in Dirty Dancing , the father of Jennifer Grey’s character
Not long before she landed the role of Lucy Ewing in Dallas, Charlene Tilton had a bit part (along with a couple of other girls) as a bathing beauty on Fernwood 2 Night.
Oh-my-God! :o If you can find a clip of this on YouTube, I’ll buy you dinner at Scott’s in London. One used to be there, but now I don’t see it anywhere. 
He was also Kramer’s friend Stan the Caddy on Seinfeld.
Can’t find the clip, but here’s a still:
Technically, of course, a gunboat is not a ship. 
What does U.S.S. stand for?
Good question. :dubious: 
Submarines are technically boats as well, but they’re also prefixed USS.
I don’t make these things up, I just parrot them!
The girl on the right looks familiar too. Is she Susan Anton? :dubious:
U.S.S. - United States Ship.