An interesting and exceedingly-rare picture of C.T.C members in uniform, source is Flight, 9 Oct 1941.
Interesting that some of the men are wearing Service Dress peaks, instead of just forage caps. Perhaps a status signifier? Note that the tunic buttons appear to perhaps be either black bakelite, or (possibly) brown leather covered, as per the dress regulations for Special Duties civilians in RAF uniform. However, the belt buckles are in contrasting brass.
Note the evident lack of any rank insignia (which is annoying) and also the absence of any 'USA' or 'CTC' emblems worn on the sleeves. Perhaps an initial issue photo-opportunity?