Computer CRT monitors, printing, computer projectors, styluses, and networks — often, we think these things were invented towards the later half of our computer history, but in fact they have been around for a long time.
Built in the 1950’s, SAGE (Semi-Automatic Ground Environment system) was using these things. SAGE was the first computer to use many of these things, and the first computer to use a screen. Why? Nuclear bomber
aircraft threats were such a major concern during the cold war, we built a computer system to help us track radar data all over the US to determine if traffic is friendly or not.
The CRT displays (or as they called them, ‘”scopes”) were so dim and with such a low refresh rate that they were operated in rooms with dim blue lights. Still, it was live display technology – a totally new idea in computing and complete with an ashtray and lighter. SAGE was also capable of connecting with other SAGE computers through telephone lines to exchange important data.
A video from the US Air Force describes the system in detail, see here: