Thanks All. I thought the T.21 would run the -31 a close second! My reasoning for the -31 is based on the fact the RAF had more 31s than 21s. It took delivery of 126 Cadet TX Mk.3s between 1951 and 1959, and operated them up to around 1986, and as most of those flew well in excess of 25,000 flights each (of which the vast majority were air experience flights) I think that just the Air Cadets’ TX Mk.3s flew in excess of three million launches! There were also quite a few civilian ones. Impressively, an ATC Mk.3 is on record as having logged a staggering 120,000 launches!