You don't need GCSE's because naval training is so good. When I was in the RNXS I learned more on a day long Comms training course than I had learned in a month at school! I still have a very high regard for it - though it may have changed a bit since the early 1990s.
The navies approach to training is very good. If you join a branch with no formal qualification requirements you will receive all the training that you require to allow you to do the job.
This will be classroom based then supervised on the job training. In some trades you will be tested for all standard learning barriers as part of the NVQ key skills and helped and coached as required to reach the required level.
The navy must be getting desperate to take recruits without GCSEs. In this day and age the exams are so easy that not to get any must be almost impossible. Maybe the RN could get the education department to introduce a few more options like:
GCSE Plate Laying
GCSE Deck Painting
GCSE A Level Bed making
GCSE A Level Heads operative