[Graham Boak]

Sorry Franek, but I assure you, as someone once professionally involved in aircraft performance and drag estimation, that the weight and surface finish of paint on an airframe is a factor: less so on a fighter than a bomber because of its small size, true. Yes, the weight of the pilot would be more noticeable but lacking UAV Spitfires that would be an operational matter for the unit. A more skilled pilot could compensate for any excess avoirdupois. Another step would be taking out the outer mgs and reducing the number of cannon shells - I would be interested to find out if this was done. Lacking such features suggests that what we have is more likely an experiment in the benefits or otherwise of natural metal finishes.

I'm not sure how much puttying was normally done on production Spitfires, other than gap-filling - the primer being part of the part of the paint counts towards the weight. On Mustangs the leading edge was puttied and smoothed in an attempt to maintain laminar flow as far back as possible. Spitfires have a join on the leading edge which would tend to spoil this. In general, Mustangs were built to a higher standard than Spitfires - or indeed any similar type.
When the Spitfires in Alexandria were used to counter Ju 86s then these were puttied in an attempt to smooth irregularities in the surface. Here the paint seems to have been polished/rubbed smooth rather than the airframe stripped to bare metal. However, the Ju 86s were long gone before the time this thread is referring to. I think the Ar 234 is the most likely candidate requiring such measures, although perhaps the Ju 88T is a possibility. The other type involved was the Me 410, but catching these seem to have been within the capabilities of the standard Spitfire. Perhaps this is an opportunity for specialists in Luftwaffe reconnaissance to comment?