From the start of the war one organisation was responsible for instruction and supplying equipment for all UK Service Units likely to come into close contact with the enemy and hence face the possibility of capture, MI9. It was later also responsible for the interrogation of captured enemy personnel and for the dissemination of intelligence derived from both those and our own POWs.
The most prolific customer was the RAF, for reasons already discussed, to the extent that the basic MI9 training course for Instructors (Intelligence Officers in the RAF case) was known as the RAF Intelligence Course B. Early RN and Army resistance (mainly based on the supposed adverse effects on morale of stressing the possibility of capture) dissipated as the war went on, though RN D-Day personnel were excluded as it was assumed that the beaches to which they operated would be in Allied hands permanently!!
Allied Naval Commander Expeditionary Force in February 1944 directed that pre-capture training should NOT be given in general to Naval personnel training for operation "Overlord". His reason was that the time was limited and that, as R.N. and R.M. personnel would be operating off beaches already in our hands or to be occupied by our forces as a result of the operation, the possibility of their capture was a remote one. In actual fact, through the cooperation of G.O.C. Royal Marines, a large number of R.M. crews of minor landing craft were covered by M.I.9(d) before joining their vessels.
MI9 Historical Report - Arcre