GMorrison
Where's Capn Mac when we need him;
Today, it was CA work on $30 million worth of projects trying to go vertical. Sigh.
If I remember rightly, Bismark was, to use an aircraft term, a bit of a "hanger queen." She sortied, but never for very long, and wound up tied to a pier afterwards for nearly the same amount of time she was at sea.
Which is plenty of time to chip rust, reprime and repaint. And, pierside, even the hull can be looked after. On top of being the prize of the fleet and the personal pet of el hefe himself. While surface Reichsmarine officers were often aristocrats, the surface sailors considered themselves no mere menschen, but superior sailors, and took great pride in their ships. Not the sort to wait until the Unteroffizier organized a painting party.
It's also early in the war, so the quality of materials had not begun to slack off.
Now, she was a tad nortorious as a "wet" ship with her low bows. So, the bows ought to be darkening, grimed up a bit with some salt crusting. But, actual rust, visible at 1/350 scale sorts of viewing distance is highly unlikely.
Grime washes would probaly be entirely appropriate. Heavier on hull and foredeck. Much lighter trending up the super structure. Really, a person could actually apply a 'white' wash (think inverted grime wash) to the uppermost surfaces.
The bunker fuel oil available was still high-quality, too. So, stack grime is going to be very minimal. All of the armament was cleaned after firing, so, no muzzle grime, either.
Oh dear, I fear I've rather rained on the weathering parade here. But dot washes on the hull would be appropos. I'd be inclined towards some unique hues--purple & green and the like to wash in, to give a good "been to the north Atlantic" feel to things.
Well, that that a well worn-out 2¢