This is an example of a "Lifeguard" periscope, a patented design produced by F. Duerr & Sons. The British company typically produced fruit jams and marmalades, but manufactured these for the duration of World War I.
Periscopes were incredibly useful tools in trench warfare, as it allowed soldiers to peek out of the trenches without the risk of being shot at. This particular design allowed for increased portability over traditional wood periscopes, which were bulky and harder to transport.
Though they were approved by the British War Office, Lifeguard periscopes were not standard issue items and soldiers would have to buy them with their own funds—this is likely why this periscope's owner felt the need to inscribe his name on it.
A Certificate of Authenticity accompanies this item.
The mirrors are a bit fogged, but the periscope still functions!
It consists of two steel plates with mirrors on the inside, connected by two sets of collapsible steel tongs. The front plate is embossed with "THE LIFEGUARD PATENT PERISCOPE SOLE MAKERS F. DUERR & SONS MANCHESTER S W." It also features a hand engraved name and rank, "Brigadier General Howell," who was likely the original owner.
The item measures 4.5" long x 4.25" wide x 2.25" tall when collapsed, and expands to be 25" tall.