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My impression of a submarine’s visual acuity was similar to a telescope: Square-jawed 1950s movie stars peering into a binocular-like apparatus suspended from the ceiling, ordering torpedoes to be fired. During and prior to WWI, submarines were just coming into their own, and would soon be the secret weapon to turn a war’s direction. The periscope, according to the image above, operated quite differently than my memories of mid-20th-century naval war movies. A bowl-shaped mirror was lifted, at the top of a tube, above the surface of the ocean. It reflected light down the viewing tube, projecting it, a’la camera obscura, on to a white tabletop for review by the captain and his officers. The bowl-shape projects the distended, distorted view seen in the image above. While this afforded an instant, at-a-glance view of the submarine’s surroundings, it did not provide the rangefinding, weapon-aiming, or navigation facilities that a modern sub enjoys. From The Book of Knowledge, published in the 1910s.