Spock, that depends entirely on what trade you are leaving and what trade you are going to?
When I changed, I had already done my Phase II Infantry, my Phase III Log, and was about to go on Phase IV Land Log and Finance Officer. When I changed, I did the Finance Officer course, but had go back and do MARS Phase II, and MARS Phase IV Common. Then it was my OPME course (which I would not have had to take as an army guy) and after that, it was Supply Officer Course followed by Phase IV Sea Logistics. THEN, it was a year long afloat training phase as Assistant Log O on a ship followed by a rigourous oral qualification exam conducted by 6 commanders and captains (navy).
Because of the timing of my change, and the path of it, I had to do an extra 5 major courses, a year at sea, and the qualfication board. To put it in context, my mates were fully qualified army logistics officers at the end of August, 1997. I wasnt fully qualified until three years later.
Your path will likely be different, but before you jump onboard, make sure you do all your research in advance, as it could have long term repercussions.
Yours, Aye.