EOTB,
Think it breaks down like this;
Acting rank, doesn't change the price of fish.
Return of Service is enforcable as you sent a joining letter in response to your appointment (dark blue speak I'm afraid)
which you signed, therfore accepting the required return of service for that particular course, which you were informed of on the Appointment letter. If you therefore leave you are backtracking on that agreement and therefore have to "Buy" yourself out to recompense the crown for a tiny proportion of the cost of the course or sty until the end of that return of service
Not a Naval Barister by trade but believe this is about right!!
