Special typewriters were used by radio telegraphist to transcribe Morse messages onto paper. In the US Navy these special typewritters were known by the slang word "mill typewriters". A special "mill" would typically use 9 point sans-serif capital letters only and have numbers "1" and "slashed 0" on the top row (not usually found in standard typewriters). The mill was usually located in the radio room on board a ship or submarine.
The Underwood Typewritter Company made several mills during history, being this model the one mostly found in wwII US Navy ships' radio rooms. The Mill typewriter history and presence goes in parallel with the use of of Morse code by the US Navy telegraphists. There is not much information to know when it began and ended, however it most likely spans from wwI to wwII. This fine and rare example was found by TechRocket Radio Museum after many years of research as they have become very difficult to find and it is in complete original, operational and unrestored condition, more than cleaning and greasing.
9 point sans-serif capital letters only and having numbers "1" and "slashed 0" on the top row, special for transcribing Morse code.
Transcribing Morse code by telegraphist at US Navy ships' radio rooms.