I’m watching a ton of WW2 documentaries and can’t help but think why they didn’t make a counter to the German Uboats other then depth charges and the hedgehog. Surely with the money and resources the US or other countries could of made a sub during that time.
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Others have well covered the sub v sub history, so let me cover some details.
WWII [Liberty ship](https://en.wikipedia.org/wiki/Liberty_ship) – 441 Ft / 136 M long, 27 Ft / 8.5 M draft
WWII [Balao class](https://en.wikipedia.org/wiki/Balao-class_submarine) sub (USA) – 331 Ft / 101 M long, 27 Ft / 8.5 M draft
Note the Liberty ship would cruise at 10 Kt (convoy) which means it moves it own length every 26 seconds. The Balao could move about half that speed submerged (8 Kt emergency, usually 5 or less), so 20 seconds to move it’s own length at 5 Kt.
Combat: The surface ship is a 30 foot high x 400 foot long target as seen from torpedo view. Set the weapon to 20 feet and fire. Unless it changes course, you win. The USA [Mk 14 Torpedo](https://en.wikipedia.org/wiki/Mark_14_torpedo) (similar numbers for German) moved at 31 or 46 Kt for long/short attacks out to 9000/4500 yards. This meant a run of roughly 600 or 195 seconds at maximum. A long attack vs a Liberty ship means 23 ship lengths, short 7.5. Lots of things can go wrong. Plus, you are moving well into the gun range of escort destroyers and similar.
Now combat vs sub: Similar numbers, but only if the target is surfaced. If it dives, the Balao now has 20 feet or more or water over the deck, so the torpedo would pass right over unless it hit the conning tower — less than 10% of the overall length. So the problem for sub v sub is where to aim and how deep.
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