bombsight — a mechanical or electronic device in an aircraft for aiming bombs
periscope — an optical instrument for viewing objects that are above the level of direct sight or in an otherwise obstructed field of vision, consisting essentially of a tube with an arrangement of prisms or mirrors and, usually, lenses: used especially in submarines.
radar — Electronics. a device for determining the presence and location of an object by measuring the time for the echo of a radio wave to return from it and the direction from which it returns.
sight — the power or faculty of seeing; perception of objects by use of the eyes; vision.
sonar — a method for detecting and locating objects submerged in water by echolocation.