https://www.wearethemighty.com/mighty-history/only-underwater-submarine-battle/

https://nationalinterest.org/blog/the-buzz/the-true-story-the-only-underwater-submarine-battle-ever-23253

https://en.wikipedia.org/wiki/Sinking_of_U-864

https://en.wikipedia.org/wiki/German_submarine_U-864#:~:text=While%20returning%20to%20Bergen%2C%20Norway,another%20while%20both%20were%20submerged.