At a later stage, select those with the aptitude; put them on the General List, and give them the education they will need in more senior positions
I think this is what we pongos used to call "Staff College"; I did hear that the RAF/RN equivalents have now been combined with the Army's College, but maybe I got that wrong.
If right, how does that work? I cannot imagine sitting down to Dinner with the risk of having someone, probably RAF, beside me holding his knife and fork wrongly. In itself that's manageable, one can always advise discreetly, but would the bounder have anything interesting to say? What's more, he might even be a woman!! After all, there is one of those now in charge of a Sandhurst College. Need I say more?