Periscope

A periscope is an optical device that allows someone to see objects that are not in their direct line of sight. Commonly used in submarines, it consists of a long tube with mirrors or prisms at each end. One end is positioned above the surface, while the other stays submerged. Light enters the top, reflects off the mirrors, and allows the viewer to see above the water without being detected. Essentially, it enables observation from a hidden or lower position, making it valuable in various applications, including military and surveillance operations.