It’s only an obvious deathtrap to us based upon our knowledge of the evolution of submarines. Back when it was built, short of water pouring in through the seams, would you have had the same thought since it was “state of the art” and you were most likely living on the coast working on sailing vessels.
Yea, I guess part of my bias is because I worked at a boiler-works one summer. They had me crawling inside of the boilers after they welded the end caps on so that I could chip the slag out.
I soon learned that I was claustrophobic as all get out!