Routes to Navy JAG Corps
There are a variety of ways to become a Navy JAG. Start with these links below.
Best resource is your ROTC POC. In general, NROTC programs feed new junior officers into the warfare communities. The Navy does not take in most of its JAGs from NROTC or a SA - to my best knowledge.
Keep in mind the JAG Corps is a small percentage of the Navy officer community, and thus takes only a handful in each year from the various options.
(1)
http://www.jag.navy.mil/careers/careers/opportunities_lep.html
This is the one where you enter your warfare community, meet all requirements there, serve a requisite amount of time, etc., then apply for the Law Education Program (LEP). I've known a few people who have done this. They had superb performance evaluations, killer LSATs and great recommendations. Much depends on the needs of the Navy, because even if you have all the right stuff, JAG might not need that many new officers in your application year. Also, if your warfare community needs you to ensure endstrength in certain grades and year groups is at the right level, you might not be allowed to transition out of your warfare community to JAG. If you can do it, it's a great way to go, but a highly competitive route.
(2)
http://www.jag.navy.mil/careers/careers/opportunities_da.html
This is for people who have got their college and law degrees. Some officers do some number of years as warfare officers, get out of the service completely at some point, use their federal and state veteran's education benefits (Montgomery GI Bill) to obtain a professional degree and then apply to come back in as a JAG. Obviously, these candidates, as long as grades, LSATs and their past military performance criteria are top-notch, are very attractive to the Navy. Or, they may just use their benefits and go on to a successful law career in the civilian world.
(3)
http://www.jag.navy.mil/careers/careers/opportunities_sp.html
This is the Navy JAG Corps Student Program, where the law student is designated as being in the inactive Naval Reserve, and have a head start on being accepted into the Navy JAG Corps. I've known several JAGs who came in via this route.
(4) And with a nod to Pima, yes, the Navy has Tuition Aid programs which will pay for after-hours night school. Theoretically, but not realistically, you could do online courses or hope your deployment/underway schedule allowed you to get your law degree after hours, and then you could apply to laterally transition to JAG Corps, but that would be a pretty evil life. Warfare officers are expected to be at sea, whether right away as surface warfare officers or after the training pipeline for other communities. All the other competitive criteria would apply.
There are probably other ways, but these are the main channels. Yes, there is an officer indoctrination course for those coming in without previous officer training and experience. I think it's still in Newport, RI.
Focus on learning what's expected and required of you in exchange for your NROTC scholarship (fingers crossed!) and ensure you are happy about the opportunities there and willing to do the required service in one of the available options. It's good to have short, mid and long-term goals, and it's equally good to flex along the way.
I am sure you know being a Navy JAG is nothing like the old TV show or even NCIS... it's a great career path, with many superb officers, who either stay for a full career or easily transition to the civilian law world with a great background.
Best of luck.