Generally, in the series like
Op Center, Tom Clancy (with
Steve Pieczenick, in
Op Center's case) created the
scenario for the books (setting, characters, perhaps some ideas for storyline), then unknown
ghostwriters actually wrote the book.
The Op Center books I would refer to as "Clancy Lite" -- some of the same excitement as a Clancy book, but no meat behind it. The fact that Clancy himself didn't write it is probably why.