From the beginning of the 20th century, however, the practical introduction of submarine navigation brought about the development of new elaborate periscopes of great length and provided with an optical system of lenses, which were built into the structure of the submarine.
In the present article, periscopes for land service and those forming part of the equipment of submarines will be described in turn.
(i) Land-service Periscopes vary much both in design and size, some being only a few inches long while others are as much as 80 ft.
Less conspicuous periscopes were therefore designed, and these, in order to take in enough of the foreground, had to be provided with a magnifying as well as a reflecting system.
Small German periscopes were usually 1 metre or 2 a metre in length and had two eyepieces giving magnifications 10 and 15 diameters.