Ex-wartime aircrew in postwar ATC.
It seems difficult to tease out exactly when ATC became a sub-branch of GD post war, but Wiki gives:
"....[RAF] Watchfield was also involved in Air Traffic Control as the School of Air Traffic Control used Watchfield between 1 November 1946 and 10 February 1950 before moving to RAF Shawbury. [4]"
Clearly the obvious people to train as Air Traffic Controllers were the large number of aircrew (with ex-pilots and navigators being particularly suitable) who had remained in (or returned to) the RAF post-war, and for whom there were no longer flying posts available. Even when I transferred from GD(Pilot) to ATC in Apl '55, I think my Course at Shawbury was 100% ex-war aircrew: every Control Tower in the land could rustle-up at least one complete ex-bomber crew from its members.
This arrangement suited everybody; the new Controllers operated in a world completely familiar to them, they knew the layout of airfields like the back of their hands, circuit, approach aids and R/T procedures were second nature to them, and they had emphathy with the post-war aircrew (who were mainly their contemporaries). In a word, they were "naturals" for this new job, and they all "spoke the same language" as 'buddies'.
From the RAF point of view it was win-win too. At their wartime ITWs all had learned basic meteorology, navigation, signals, Theory of Flight, armaments and Administration and Organisation of the RAF - and they'd had years of hard and often dangerous experience to back it up. As I recall, it was only in the early '60s that the new recruits started coming in in any number; these now had to be taught ab initio all the skills that the Old Brigade brought with them gratis as far as the training organisation was concerned.
It is not surprising that there were hundreds of these old timers around until the time I retired in '72, when the inevitable clear-out had to happen, and the new boys and girls took over.
Danny42C.