Periscopes

A periscope is an optical instrument that enables an observer to see from a position that is concealed or otherwise obstructed. It works by using a tube that contains mirrors or prisms arranged to reflect light from an object at the top of the tube to the observer’s eye at the bottom, bending the line of sight by about 90 degrees. Some designs use prisms instead of mirrors to improve light transmission and image quality; modern variants may include lenses to magnify the image and, in some cases, electronic components to transmit video.

Two-mirror periscopes are a common basic form, but military applications have driven the development of longer, more rugged systems. The best-known example is the submarine periscope, a long, protected tube that reaches the surface to provide a view while the hull remains submerged. Submarine periscopes may incorporate rangefinders, night vision, or image sensors, and many contemporary models can deliver video feeds to displays at the operator’s station. Periscopes are also used in tanks and other armored vehicles to give crewmembers a protected forward view, and in a variety of inspection and surveying tools.

The word periscope derives from the Greek peri, meaning around, and skopos, meaning watcher. The concept appeared in early modern optical writings, with practical periscopes developed in the 19th and 20th centuries and widely deployed during the world wars. Today, periscopes remain in use in naval and land-based platforms and in certain specialized inspection devices, preserving the core function of viewing from a protected position.