A periscope, is a optical device for conducting observations from a concealed or protected position. Simple periscopes consist of reflecting mirrors and/or prisms at opposite ends of a tube container. The reflecting surfaces are parallel to each other and at a 45° angle to the axis of the tube. The Navy attributes the invention of the periscope (1902) to Simon Lake and the perfection of the periscope to Sir Howard Grubb.

For all its innovations, USS Holland had at least one major flaw; lack of vision when submerged. The submarine had to broach the surface so the crew could look out through windows in the conning tower. Broaching deprived the Holland of one of the submarine’s greatest advantages – stealth. Lack of vision when submerged was eventually corrected when Simon Lake used prisms and lenses to develop the omniscope, forerunner of the periscope. Sir Howard Grubb, designer of astronomical instruments, developed the modern periscope that was first used in Holland-designed British Royal Navy submarines. For more than 50 years, the periscope was the submarine’s only visual aid until underwater television was installed aboard the nuclear powered submarine USS Nautilus.

Sir Howard Grubb
Thomas Grubb (1800-1878) founded a telescope making firm in Dublin. Sir Howard Grubb's father was noted for inventing and constructing machinery for printing. In the early 1830s, he made an observatory for his own use equipped with a 9-inch (23cm) telescope. Thomas Grubb's youngest son Howard (1844-1931) joined the firm in 1865, under his hand the company gained a reputation for the first-class Grubb telescopes. During the First World War, demand was on Grubb's factory to make gun sights and periscopes for the war effort and it was during those years that Grubb perfected the periscope's design.

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French soldiers in Alsace using trench periscope.
Trench periscope.

Photos courtesy of "Photos of the Great War" website

Interior of a British submarine with periscope.