Why Bismarck might zigzag against an unlikely submarine

Bismarck's zigzagging could reflect uncertainty about British submarines as well as an attempt to shake shadowing cruisers, even though most Royal Navy boats guarded ports and return routes.

Question

Was Bismarck zigzagging only to lose the shadowing cruisers, or might the Germans also have feared Royal Navy submarines?

Short answer

They could have feared a submarine even though one in the mid-Atlantic was unlikely, because Bismarck could not know the actual British deployment.

Notes

The maneuver need not have served only to lose the British cruisers following Bismarck. German officers may also have allowed for a Royal Navy submarine threat. A British boat waiting in the mid-Atlantic was unlikely, but Bismarck's command could not know that none was present. Most British submarines were positioned nearer French and German ports and the routes back to them, showing how the real deployment and the threat perceived aboard the target could differ.