The next step is to get yourself good and aquainted with the mission editor and then building missions and uploading them to give back to the community. I imagine you being an ex-submariner, you could probably come up with some pretty realistic mission setups !
(Something I've just started working on for Dangerous Waters)
Then beyond that, maybe learn how to do some database editing and do some modding. (Something I plan for the future)
I'm working more with Dangerous Waters but I still play quite a bit with Sub Command when I'm in the mood.