(Source - A4 mate at Halton
OrgASMic
I believe the roundel is for PCS "blues" about to be trialled by Supply and Movements Trg Wg (SMTW - or A4 at RAF Halton). There is no other A4 at RAF Halton as the rest are Serco! The blue PCS is supposed to be similar to that worn by the D-Boats (DARING, DIAMOND, DUNCAN, etc...) who wear the Ship's crest on their right arm - I would expect this is what the roundel will replace?
LJ