Blackhawk mom, try searching on
"service selection" in the USNA forum. There have been several germane threads and detailed posts about the process in recent years, as well as stats posted about what percentages of a particular class got their first choice of service selection (Navy surface, Marine air, etc.).
Service assignment is the actual ship or pipeline school date.
Bancroft Hall is one of the most lively rumor mills in existence, and hearsay thrives. It seems to me over the last several years, the vast majority of mids have gotten what they wanted. No doubt some are disappointed, but that's the deal coming in. We had a sponsor daughter a few years back who really, really wanted Surface Nuclear Power. She didn't get it. She's a very happy conventional Surface Warfare Officer who just got selected for command at sea, a major career milestone.
I wouldn't say there is a "course of study" that leads to one area. Service selection is a coming together of needs of the Navy and Marine Corps on the one side, and the track record (class standing), achievements, and choices of summer training and other activities on the other. Some warfare communities require additional hoops to jump through, such as physical skills screeners or interviews. Everyone gets their B.S. in one (or more) academic major. Everyone gets the briefs on the service warfare areas, the service selection process and the options available. Everyone makes choices along the way about summer training. The 2/C and 1/C summer cruises and training are really designed to help the midshipmen make an informed choice about the best fit(s) for their service selection. A plebe may start out coming to USNA bound and determined to be a naval aviator, but changes his/her mind after being exposed to Marine things and Leatherneck during 1/C summer. That same plebe could find himself medically dq'd for air during 2/C year, and have to find a new path. The ac year experiences and summer training are designed to let mids try things on for size and make their best informed choices. After that, it's the one reliable constant in military life: the needs of the Navy and Marine Corps will govern how many ensigns and 2LTs they need in particular flavors any given calendar year from all sources, including ROTC, OCS and other commissioning programs.
There is not much you can do except be supportive as the years go on, and your mid travels the road of thousands before him. Each year, and each mid's experience, are unique. The long view is to look at this uncertainty as good training for life in the military. I knew I would move every 2-3 years, just wasn't sure where or to what assignment. It's the same process - I would fill out an Officer Preference form online (commonly called a dream
sheet), discuss options with my detailer (assignment staffer), hope I did everything that was required to go to a certain type of job, and hope the needs of the Navy coincided with my own at that particular juncture in time.
There is plenty of help on here from current mids, alumni, BGOs and parents of post-service selection mids. Factual knowledge is power!
O Wise Mod: this thread might better live in the USNA Forum, as I'm sure the processes differ from SA to SA.