True, but if you are doing anything that involves conflict with Germany's best you would always use squadrons which had the latest model. The RAFs front line strength of Spitfires was rarely more than 1000 in Europe. The wastage of fighter aircraft in WW2 is hard to believe in the modern era. A Merlin engine was in need of overhaul after 250 hours service, some were overhauled but many more were just replaced with the latest model.Spitfire XIV as opposed to Spitfire V which was the most numerous Fighter Command fighter until 1943. Less than 1000 Spitfire IX's were built between 1942 and 1943 and these had to be allocated between Britain, the Commonwealth, our European allies and the Americans being assigned to both the ETO and MTO. In my comments, I should have made it clearer that I was referring to the use of the slipper tanks by Spitfire V's, although I thought the restrictions on the larger tanks use continued.