Special Features:

Used on submarine periscope

Properties:

An optical instrument designed to displace the line of sight in a vertical plane when eye level vision may not be practical or possible, as in intrenchments, tanks, submarines, and the like. the raised line of vision is obtained by the use of mirrors or prisms within the item, permitting a line of vision on a plane other than that of the observer. it may have a single or dual optical system(s).