Thinking back to the immediate postwar years, sheer necessity and the pressure of events must have played a part in driving straight-through conversions to the left seat. For example, all of Bomber Command's 4 Group was transferred to TC on 7 May 1945, as the war in Europe ended, in anticipation of a need to transport troops to the Far East - so Halifax pilots found themselves becoming Dakota pilots after a quick type/role conversion. Then in 1948 came another TC expansion to cope with the Berlin Airlift. When that was done, the transport role had to take a decided back seat as the RAF created its Canberra medium bomber force and, later, the V-Force. With a degree of 'stability' forced upon it, I imagine it then became feasible for Transport Command to insist on pilots doing co-pilot tours before graduating across to the other seat.