For most people, the word "periscope" probably conjures up images of a submarine. A submarine periscope is a tubular optical device that is raised above the surface of the sea from the submarine and used to observe the surrounding area. In other words, a periscope is a device that allows high locations to be viewed from a low position.

As for the optical path of the periscope, the light from the objective lens is directed 90° downwards by means of a prism. A relay lens inside the tube relays the image. A prism in the eye-piece then redirects the path of the light back into the horizontal plane and into the eyes of the observer.

Nikon has manufactured numerous periscopes for industrial use and for application in specialist fields. The shinkansen periscope is one such example.

The first shinkansen periscope was built in 1966 at what was then the Tokaido Shinkansen Tokyo Operations Depot. This depot was near Shinagawa Station. The shinkansen periscope was used to check whether the pantograph, which is installed on the roof of a shinkansen car, was raised or lowered. At the time, cars of the 0 Series shinkansen were approximately 4 meters tall. The vantage point for inspection of the pantographs needed to be set higher than this.

As the pantograph is raised and lowered, current flows in the overhead power lines at a voltage of 25,000 volts. Using a periscope allowed the observer to avoid the risk of electrocution that the proximity of the overhead lines might otherwise entail.

The use of periscopes on the shinkansen was certainly necessitated by the height of the cars and the danger from the high-voltage overhead lines. However, there was also an additional reason why periscopes were needed, a result of the distributed traction system that is a distinctive feature of the shinkansen. The shinkansen was comprised entirely of cars that were motive power units. This system—which was unique to the shinkansen—was the method chosen to make high-speed rail travel a reality in Japan, a country whose railways feature many curves and gradients.

Incidentally, coupling a motive power unit to the foremost or rearmost car in a train is known as a concentrated traction system. This system is standard on high speed railways in the West, where railway lines are usually straight and the stations far apart.

In the longest 0 Series shinkansen formation, which consisted of 16 cars, eight pantographs were required to supply power to each two-car unit.

A single shinkansen car is approximately 25 meters in length. To put it another way, to visually inspect all the pantographs on the longest (16-car) formation would require the observer to walk approximately 400 meters. The shinkansen periscope enabled rapid inspection and allowed reliable visual checking of the rearmost pantograph from the foremost car.