Tom Clancy Games Crossovers

Now, I am not an expert in Tom Clancy games by any means. I have played all the Splinter Cells, but even those details are a bit foggy in my memory. I have played a couple Rainbow Six games....but that's about it, so I was curious...Are there any Crossover Tom Clancy games? Either where characters/teams appear in one game...or where storylines from one game are explored in more depth or referenced in another?

I know Hawx begins with a crossover of Ghost Recon Advanced Warfighter, but was wondering if there were other instances like this.