Originally Posted by Chu Chu
I'd have to guess that the Sunderlands were designed from the ground up to be more tolerant of salt. Things like avoiding contact between dissimilar metals where possible, using more corrosion-resistant alloys, avoiding closed areas of the structure that can trap salt, etc. None of that could completely prevent corrosion, of course. But if it came down to something sprayed on, they could have just loaded the salt in a C-54 and sprayed it afterward (and/or before).
They might have used magnesium for cathodic protection, much as ships use zinc for the same purpose. However, casting a casual eye over https://en.wikipedia.org/wiki/Galvanic_anode
suggests that there's rather more to it than just slapping a few bars of magnesium all over the airframe; there's a risk of hydrogen embrittlement, which would be just as bad for an airframe as salt corrosion.
I recall what a friend told me about the effort to get Apaches operating from RN aircraft carriers; they had to seriously beef up the ships' freshwater generating plant so that they would have enough to wash down the aircraft adequately afterwards. Such as the problems of putting an airframe not designed for maritime operations anywhere near salt water...
Years of bitter experience fighting the rot in airframes put the RN of magnesium alloys for good, and there was much sucking of teeth from the older hands when it was suggested it would be good to fly Apaches from their decks. An old chum of mine used to be a RN photographer, and for yonks his job was taking pictures of hard-to-access recesses of airframes and sending the photos of ugly growths of corrosion back to the factory for assessment. Often as not the assessments came back as "Do not fly. Ever. Again", or words to that effect!
Duxford's just over the way from where I live - I'm now curious to take a look at their Sunderland to see if there's anything obvious! But I suspect that the tricks they used then are pretty much the same as are used these days for carrier aircraft, which are pretty much as you yourself outlined.