You can look it up in the history books - but in a nutshell, in the late 1800's Torpedo Boats were developed - similar to the PT-Boat of legend. Then a ship type was developed to hunt and kill them - a Torpedo Boat Destroyer. Then they mounted torps on the Destroyers ....
VERY simple timeline - and somewhere in there a bright guy came up with a way to get the torps past the destroyers - submarines .....
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