Submarines (especially U-boats) played a important role in developing undersea operations as well as changing naval warfare. Gone are the days where all enemies can see each other eye to eye. The development of submarines especially in world war I allowed for submarines to stay longer, take the pressure of water better, and attack enemies better. Torpedoes also got an update that allowed them to shoot straighter, and smaller so that more can be loaded.
However, that is not too say, that u-boats are the only ones that benefited. In a way, ships and planes also developed. The development of Sonar allowed planes to spot submarines and bomb them, as well as for ships to drop depth charges or avoid submarines all together. Ships also were given disruptive camo-patterns that allowed them to have a higher chance of surviving even without weapons loaded on board.
While U-boats during World War I was fairly limited in what they were able to do, they paved the way to a whole new military branch, and changed the dynamics of war in the sea.
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