Pocket Battleships were a term to describe larger warships that were listed as light enough to qualify for the requirements under Versailles treaty. Of course, they exceeded the requirements. Bismarck was created after Germany officially tore up the treaty.
US diving crew finds wreck of British submarine
HMS Olympus struck a mine and sank, 8 May 1942.
May they rest in peace. But it is a little strange that the article describes this as “one of the worst naval disasters of the second world war”. Numerous other ships went down with far more casualties.