Paul Traeger Discusses the Periscope
WWII submarines traditionally had two periscopes; a navigation or observation periscope and targeting, or commander's, periscope. The observation scope, used to scan the sea surface and sky, typically had a wide field of view and no magnification or low-power magnification. The targeting or "attack" periscope, by comparison, had a narrower field of view and higher magnification. In WWII and earlier submarines, it was the only means of gathering target data to accurately fire a torpedo, since sonar was not yet sufficiently advanced for this purpose (ranging with sonar required emission of an electronic "ping" that gave away the location of the submarine) and most torpedoes were unguided.