1] R.C – radar control : in the early days of the radar branch it was divided into ‘plotting’ and ’control’. RC ratings specialised in the use of fire control radar for the guns
2] GPO London was the normal postal address for servicemen, i.e "HMS Rodney, GPO London" - the mail was then directed to the barracks at Mill Hill, London, where it could be forwarded to wherever the ship was. I cannot explain the BREE bit ...
3]
V.B. = perhaps Victory Barracks (the naval barracks, Portsmouth)?
Radex probably refers to the building known as Radex House ( = RN Radar School, Portsmouth)
Philadelphia is curious – was he at Gibraltar at the time? the USS Philadelphia was there at about this time I believe
Eastney probably means Fraser Gunnery Range which was located at Eastney, Portsmouth
see:
https://fraserrange.co.uk/history/4] HMS Pembroke was the naval barracks at Chatham and had no particular radar connection. The only connection to Bletchley Park that I know of, is that the WRNS posted to various ‘secret’ establishments, such as Bletchley, were shown as serving at ‘Pembroke V” ( that’s a V meaning 5)