Okay, let me do you a favor, before the entire board gets home from work and jumps down your throat. Please, use the search function and try words like "transition", "helo to jet", etc etc. This subject come sup pretty much once every two months.
That said, platform transitions are not unheard of. For example, the S-3s are going away, you have a bunch trained aviators, you need to put them into new platforms. OK, what about guys in platforms not going away? Transitions for the sake of "I want to go fly this" or "I selected XXX and am qualified in it, now I want to go fly XXX" are not what I would call common. Look at it from the Navy (or Marine) perspective. The gov. pays however much money to train you up in your selected platform. You decide to try to transition, what does the Navy get? Instead of someone with 3-4 years of operational experience under their belt, ready to do a shore tour, and then possibly select for Department Head and go back and use all that operational knowledge to train nuggets, they have a guy in his 6th or so year in the Navy who basically wants to start over (Sundown guys I AM NOT TALKING ABOUT YOU).
Then you have to ask, who should we let transition? Your community is not gonna send some dirtball, but then again, why should they pawn off a rock-star quality guy who will make them look good by staying in the career path and going on to the FRS or some other high-profile job within the community (notice how I keep using that word).
Bottom line, transitions happen. Rarely.
Now, use the search function and wade through the other posts out there, they have a ton of great info. Everyone else, lets play nice and not jump all over goplay234.
[and if you just have a desire to fly a few different airplanes, you can do so on your shore tour. Station pilot, Test Pilot School, Personnel Exchange Program (flying with foreign nations), SAR station pilot, range control aircraft...)