F169 - the new system was designed to tie in with Chapter II ("Masters and Deck Officers" of STCW 95 - the 1995 Amendments to the "International Convention on Standards of Training, Certification and Watchkeeping for Seafarers", as defined by the IMO, part of the United Nations.
This meant in theory that, if you ticked the right boxes, your RN qualification was recognised by the Red Ensign types (or Liberian ensign!) worldwide and - subject to a few extra modules such as loading, passenger liaison and 1st Aid - could be transferred. In practice, it has been a bit harder to get civil recognition of naval qualification, because they don't seem to recognise time on warships as counting towards the minimum qualification periods for certification.
But to answer your question, from memory, as I do not have access to the DCIs at home, and I cannot find any reference to STCW on the pisspoor RN webshite.
After 8 months as a YO on Common and Specialist Fleet Time, (different Task Books for both halves and with a brief "Initial Warfare Officer Navigation" Course between the two) and a pass in his Fleet Board, a baby Warfare Officer goes to HMS COLLINGWOOD for his Initial Warfare Officer Course (previously called Junior Warfare Officer Course, X Course, and OOW Course). The first part of this is a week's assessment (the "Nav Sea Week") in the bridge simulator of basic OOW skills and bridgemanship, which if successful leads to award of...
The Navigational Watch Certificate (NWC). This is a prerequisite to keep a watch on a warship or take "charge of the ship" (although not unsupervised - only if he passes his Platform Endorsement (see below), and has the confidence of the CO, then can he keep a watch unsupervised in (and I quote) a "benign warfare environment"). Because of the beefed-up Astro content of Specialist Fleet Time, and an exam taken in Nav Sea Week, this is equivalent of the old Ocean Navigation Certificate. Your Qualifying Sea Service (QSS) starts from the day you set foot on a ship with a NWC.
The next level up, equivalent to the old Bridge Watchkeeping Certificate is:
Bridge Warfare Qualification (BWQ). After 6 months minimum/12 months maximum into his first job, an OOW will sit a much harder test, which can be conducted by FOST staff, but normally by the CO, asking questions about warfare serials, berthing, shiphandling, met and other stuff. If he passes this, then he is allowed to keep watches in a "Challenging warfare environment".
An extra part of the STCW requirements is the requirement that an OOW knows all about a ship before he's allowed to keep a watch unsupervised. Thus, after a few weeks on a ship (or shorter), any new OOW (including PWOs, XO and even the CO) will sit a Platform Endorsement (PE) test by the CO and NO, to see if he knows the ships systems, can cope with Machinery and Steering Gear breakdowns, launch seboats and helicopters and conduct Man Overboard Recovery. This is just a formal way to record the CO's confidence in an OOW, is class-specific (ie T23 rather than just HMS RICHMOND) and lasts for 5 years after leaving that appointment.
The final part of the jigsaw is the Command Qualification 1 (CQ1). In a nutshell, after reaching a certain minimum seniority as a Lt (I forget the number of years), you can sit the 7 Command Exams (Navigation 1-5, Seamanship and Warfare 6 - Meteorology) for the first stage of Command. Only once these are passed, can you sit an oral board and a bridge simulator practical to assess your knowledge of everything that you need as a CO (oral grilling by a Cdr(X) about ME, NBCD, ROE, Admin, Logistics etc - practical about conduct of a ship in difficult nav/vis conditions). If you pass this (and only about 30% do first time), and have a minimum of 5 years QSS (ie seatime) since award of the NWC, then you are now CQ1, which is the same as a STCW II.2 award, entitling you to command a MCMV, Patrol Boat and (bizarrely) an SSN or SSBN. It is this that you then take to civvie street and use to drive the Gosport Ferry, subject to the extra stuff I talked about.
The qualification to command a big ship (CQ2) is a lot more exams, a lot harder oral board and bridge practical but has no extra STCW award tacked onto it.
Hope this helps!
EDITED to correct a typo