The title of this You Tube video misleading:
"There's only been ONE underwater sub battle in history"
NO! Not a strictly underwater battle, submarine mano-a-mano, both boats totally submerged, no optical or visual input involved..
Watch the entire video and devoted readers to the blog I am sure will agree with my assessment. This was not a strict submarine battle totally underwater as would be understood in the modern naval context.
Modern submarine warfare both vessels submerged combat dependent on passive sonar for detecting the enemy, torpedoes when fired either wire guided to target or using embedded active sonar for the final terminal guidance to the enemy warship.
THAT MISSION OF THE GERMAN U-834 SEEMINGLY DOOMED FROM THE START ANYHOW! U-834 STILL REMAINS A SERIOUS DANGER TO THE ENVIRONMENT, SLOWLY BUT SURELY LEAKING MERCURY INTO THE SURROUNDING WATER, ALBEIT THE SITUATION AMELIORATED TO A DEGREE BY MEASURES AS TAKEN BY THE NORWEGIAN GOVERNMENT.