Early Airfix kits didn't contain hakenkreuz, in my recollection they started to appear some time in the seventies, then disappeared a few years later. It may have coincided with the takeover by General Mills/Palitoy, or it could have been to do with meeting requirements in order to display a CE marking. This debate has been done to death on modelling forums, the long and short of it is that hakenkreuz on decal sheets or box art, even where the subject is not aligned with fascist ideology is a big no, no. If you wish to add hakenkreuz to your model the solution is to go with the aftermarket.