You are a little wide of the mark Mr. Bloggs. Im on 55 at Cranwell and ALL NCA students are now designated as WSOp. The initial generic phase of 20 odd weeks is completed THEN the students are streamed by B flight and sent on to either C flight for advanced training, or the WSOp( crewmen) selected for rotary disappear to Shawbury. The main point that the original poster may be interested in is that at the streaming stage you will be selected by a board which includes people from Innsworth, so you will be streamed on percieved strengths and also service needs at the time. To summarise: after 26? weeks your trade will be, WSOp (crm) rotary or fixed wing, WSOp(Acoustic) or WSOp(EW).
Course No 1 is running now on generic phase. Apparently in the future the chaps can return to retrain on the advanced bit, so its possible for a helicopter crewman to switch to being a EW operator on Nimrod if they choose to do so,( or the RAF needs the bodies).