Periscope is an optical instrument that functions based on the laws of reflection. Periscopes are used for observation in conditions where direct line of sight observation is not possible.
Johannes Gutenberg is stated to have marketed a kind of periscope in 1430. He is famously known for his contributions in the field of printing technology. His periscope was to support pilgrims to observe the religious festival at Aachen. This equipment enabled them to watch over the heads of the crowd.
An early periscope with lenses was mentioned in 1647 in the book on moon by Johannes Havelius. He was able to identify military application for his invention.
The credit of inventing first naval periscope goes to Hippolyte Marie Davy. His invention in 1854 consisted of two small mirrors fixed at each end at 45 degrees. Simon Lake is credited with using periscope for the first time in submarines. This was in 1902. The devise was modified in World War I by Sir Howard Grubb. Periscope fixed to rifles enabled soldiers hidden in trenches to observe the movements of enemies. Different varieties of periscopes were used during World War II.
Photonic mast is gradually evolving as a substitute for periscope. This equipment which is similar to a digital camera array has lesser physical constrains compared to conventional periscopes.