As you have some of the basics, it was Mountbatten not the North Sea - but in my recollection it was B*&^^%y cold in the water and we were dressed in coveralls with swimming trunks and plimsolls but no immersion suits.
Frankly the staff and marine craft were useless and they did not respond quickly enough - although in this case it would have been too late anyway.
One of the DS was supposed to have been kitted up for just such an emergency but was not.
There should have been two marine craft but there was only one. After they picked Howarth from the water, those of us in the other dinghy were left to drift down Plymouth Sound - next stop USA and the light was fading. Surprisingly and after the alarm was raised, where was the SAR helicopter? Eventually, we were picked up by a second craft but you may imagine the atmosphere when they handed out the course certificates.
As far as I am aware, nobody from the course was called to the enquiry/inquest but I believe some pretty searching questions were asked.
Old Duffer