Originally Posted by dyna mo

No one knew at that time that naval strategy was about to change to air. And those biplanes that dropped the torpedoes almost didn't get sent. The only reason they made it past the Bismarck's defenses were due to their flying slower than the exploding bullets were designed for. It also doesn't seem likely those sorts of airplanes would be readily available in the middle of the Northern Atlantic.

While no one knows what could have happened, we do know Britain was alone, isolated and running out most everything. If the Bismarck even only had a few months to wreak havoc via a solid naval strategy, it doesn't seem out of the question that Britain could have collapsed with a blockage like that and offensive on the island.