That seems completely thorough, accurate, and excellent logic. I'm just wondering about all metal deck...there was wood in the early days, and then they switched to crap wood...so why all metal pre war?
Good question and I don't know if there's a historical record anywhere to answer it.
But my guess is that in the early days, the old time sailors knew that wood such as teak was the best for making decks since it was non-slip and so resitant to rot. But at some point after that, when navies were switching to steel from wood, they just naturally assumed that steel was so much stronger and would always be better in every application. If they needed non-slip, they could just forge that right into the steel deckplates.
Between the wars, there wasn't much use of submarines, so that thought was kept, and the few U-boats around the Spanish coast in the 30's didn't see much (any?) action and so there were no reports of the problems with steel.
However, once WWII started, and particularly when so many U-boats were sent to Norway to harrass the Murmansk-bound convoys, it was realized that wood was still a better material for decks even on a sub. Perhaps especially on a sub since a U-boat's deck are almost always wet. Steel and water at below zero temperatures is a recipe for disaster, and I can't imagine how difficult it would be to use a deck gun on a deck with rapidly forming ice after just surfacing.
The reason they went to crap wood of course was that by this time in the war, teak, which comes from the far east, just wasn't available but pine was easily gotten all around the Baltic. It didn't matter that it was didn't last very long, it was much easier to replace even than teak. The crew could even make some repairs themselves.
