The first military submarine was Turtle (1775), a hand-powered egg-shaped device designed by the American David Bushnell to accommodate a single man. It was the first verified submarine capable of independent underwater operation and movement, and the first to use screws for propulsion.
The discovery of gunpowder in the 800's and the subsequent invention of firearms in the 1100s both coincided with long periods of disunity, during which there was some immediate use for infantry and siege weapons
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