Its doable through an inter-service transfer, although a little more complicated than traditional routes. silversnake requested a transfer to Navy, hopefully he'll add more info. As far as I know you'll still need to attend Marine OCS. Contact your local OSO ASAP -- you may have to go for an age waiver, but since you're prior you have a good chance of getting it. You'll start off by filling out at rough application, giving the OSO a copy of your transcripts, running a Physical Fitness Test, and taking the ASTB (commonly called the AIR test). From there they will submit your package to the next board. You'll be going for OCC, which is a 10-week course in Quantica, VA. Age could be an issue but I believe the age-waiver can work for you there. I don't know all the details here.. but I'm sure that someone with more experience than me will chime in.