I've just finished reading an at times disturbing book on the airborn assault on Sicily. It is clear that the USAAF C-47s used in that operation were not equipped with armour or self sealing tanks. Was the C-47/Dakota ever so equipped?
https://en.wikipedia.org/wiki/Bengal_famine_of_1943#:~:text=The%20Bengal%20famine%20of%201943%20was%20a%20famine,Bengal%20and%20eastern%20India)%20during%20World%20War%20II.
Max Hastings, in his biography of Churchill, makes it clear that he overruled the relevant ministers and the home civil...
At risk of thread creep, but in addition to cost effectiveness you could also look at the losses. I believe the Hurricane pilot was at far greater risk of becoming a casualty than a Spitfire pilot even during the Battle for France. This is surely due to the obsolescence of the Hurricane.