I have recently purchased a photo of senior officers - Lt-Cols, Cols, Brigs etc - who attended a "Conference of C.E.S. and C.R.E.s held by C.E. Home Forces" at Aldershot on the 7th November 1941. It's a basic question from me. Can someone please give me the expansion of those acronyms? The supplementary question is, does anyone have more detail on what the conference was all about, please?