Formed in 1888, Glasgow company Barr and Stroud were the UK's leader in optical rangefinders and supplied the British Army.
By Hayley Millar
Business correspondent, BBC Scotland
Now part of the French defence firm Thales, the company is based in new offices by the Clyde.
The first Barr and Stroud periscopes were produced in 1888
But despite the modern interior, the company's mini museum of periscopes transports you back to the late 19th Century.
In pride of place, its brass shining, is the fifth one ever made by the company.
In 1916, the Royal Navy asked Barr and Stroud to apply its range-finding technology to periscopes.
As a result, the periscope was transformed from a simple optical "looking stick" into a major component of submarine warfare.
That relationship with the Navy still exists today and has been central to the evolution of the periscope.
During World War II, periscopes helped British submarines sink almost 500 enemy ships and damage 100 more.
But the advent of modern electronics brought the most rapid changes.
Royal Navy Astute class submarines will have two optronic masts
From the 1970s to the mid 90s, advances included the world's first thermal imaging periscope, the first laser rangerfinder periscope and the first fully remote control periscope.
Now, 90 years on, the image of the "steel tube" lowering through the submarine hull into the control room is almost a thing of the past.
The latest CM10 Optronic Mast has taken periscope technology to a new level.
Instead of peering into the viewfinder, the submarine commander can watch images from high-resolution television cameras and thermal imaging cameras displayed on televison screens.
Even while pitching and rolling, the crew can focus on a target using the latest stabilisation technology which can transform a roller-coaster image into an almost static one in seconds.
The Royal Navy's new Astute class submarines will have two optronic masts onboard.