Right. In order to get your dolphins awarded, you'll first complete Dartmouth, common fleet time, fleet board, specialist fleet time, then obtain your navigational watchkeeping certificate in compliance with STCW at HMS COLLINGWOOD. Then, you undertake the rest of the junior warfare officer's course, soon to be renamed. The JWO course is a little short of 4 months long. You'll then, as a future submariner, go off to HMS RALEIGH and DOLPHIN, the RN Submarine School, where you'll learn submarine systems and a few other gems. You'll then carry out about 7 weeks of training on the reactor chemistry, physics, operation and safety of the reactor type of the boat you're going to. Then you'll carry out further training in dived navigation (very different to general service nav), periscope watchkeeping, and a host of other fun subjects including the SETT, or submarine escape training tank, where you undertake a series of ascents culminating in a 30m one from an airlock to simulate leaving the boat under unpleasant circumstances.
Once you're done at the school, you'll join your boat and crack on with the real fun....
And there's an awful lot more to Perisher than the periscope.