Receiver, RG (‘Red-Green’ Infra-red, O.S. 960 G.A., ZA 23119,) monocular for Army use, in hermetically sealed unit.
In the history of war technology, this is Ground ZERO for night vision development. This British Infra-red Image Tube was manufactured in 1939 for use in the SUPER SECRET OS 960G.A. ZA 23119. The world's FIRST Military "see in the dark, infrared night vision device!"
We now think it dates from circa 1942 and was one of the earliest forms of military night vision scope. It could pick up signals from a special RG lamp. Employed by the Combined Operations Pilotage Parties (COPPs) 1942-1945 and the Special Operations Executive (SOE), it was top secret state-of-the-art technology. Such scopes were also used extensively in Normandy during the D-Day landings, presumably once ashore since infra-red does not travel well through water vapour. The primary infra-red tube was first manufactured in 1939 and preceded the American M2 Sniperscope by four years. The ability to 'see in the dark' was a chance discovery from the early Farnsworth television camera. The Khaki covering made for easier handling in the marine environment. It was deliberately manufactured to look like a military water bottle in order not to arouse attention.
In 1943 the systems name "R.G. Equipment" was replaced by the code name" Tabby". This was the general name for a number of types of night vision systems based on these convertertubes. Tabby was not some clever acronym, but merely because a Tabby cat can see in the dark!
The Tabby Type K viewer was a hand held monocular with a self-contained power unit. As the 3,000 volts required to activate the image convertertube is at a negligible current, it permitted the use of batteries that were permanently sealed into the monocular case. There were three of these batteries called Zamboni piles, they consisted of thousands of thin disc cells packed in plastic tubes. The viewer was turned on by pressing a button on the side of the case. The eyepiece could be adjusted; all the other focussing was factory set. The whole unit was carried in a very sturdy leather case, but when the batteries deteriorated or the tube failed mechanically or damaged by too much light then the complete unit was discarded.
More info you can find here: " Tabby Tales" by Clive Elliott
The original soft rubber eyecup is still attached.