<P> In modern use, specialised periscopes can also provide night vision . The Embedded Image Periscope (EIP) designed and patented by Kent Periscopes provides standard unity vision periscope functionality for normal daytime viewing of the vehicle surroundings plus the ability to display digital images from a range of on - vehicle sensors and cameras (including thermal and low light) such that the resulting image appears "embedded" internally within the unit and projected at a comfortable viewing position . </P> <P> Periscopes allow a submarine, when submerged at a relatively shallow depth, to search visually for nearby targets and threats on the surface of the water and in the air . When not in use, a submarine's periscope retracts into the hull . A submarine commander in tactical conditions must exercise discretion when using his periscope, since it creates a visible wake (and may also become detectable by radar), giving away the sub's position . </P> <P> Frenchman Marie Davey built a simple, fixed naval periscope using mirrors in 1854 . Thomas H. Doughty of the US Navy later invented a prismatic version for use in the American Civil War of 1861--65 . </P> <P> Submarines adopted periscopes early . Captain Arthur Krebs adapted two on the experimental French submarine Gymnote in 1888 and 1889 . The Spanish inventor Isaac Peral equipped his submarine Peral (developed in 1886 but launched on September 8, 1888) with a fixed, non-retractable periscope that used a combination of prisms to relay the image to the submariner . (Peral also developed a primitive gyroscope for submarine navigation and pioneered the ability to fire live torpedoes while submerged.) </P>

Submarine to view object at the surface of water