Oh, the depths of WW2 geekery...

As part of my regular Xmas I normally get a WW2 aircraft print calendar. This years has some cracking art in it and having an admiring look through it tonight on my return home, I came across this:

Spot the mistake!!!

(I did immediately, resulting in loud sighs from A - 'does it really matter??' says she - all I could do was splutter in outrage and defence! Still unsure whether to write to the maker!!! Imagine getting one of my favourite planes wrong!)