|Navy Tactical Data System|
During WWII the aircraft carrier served as the central command ship within a fleet of ships. The position of both enemy and US ships and planes were plotted by hand using grease pencils on a large clear Plexiglas screen in the “Combat Information Center”. Sailors wearing head sets received information on locations and learned to write backwards so that officers on the opposite side of the screen could interpret the “plot”.
In the 1950s the US Navy asked for bids for an automated data system that would perform a similar function using computer control of both data transmission and plotting presentation. Hughes Aircraft was selected for the display equipment, Univac supplied computers, and Collins Radio Co. produced the radios and modems for the program.
NTDS was a web-like communication network. A command was sent out from the carrier asking for an automatic response of data from various ships. Data were encoded as discrete pulses, which required precision frequency stability and timing control. Because the pulse width and spacing were fixed, upon detecting its leading edge the receiver could “predict” the next pulse (or a zero value - blank space) and regenerate the transmitted signal with no distortion. This feature thus required precise synchronization between transmitter and receiver. Collins equipment in the NTDS used those lessons learned in the Kineplex system to achieve new standards of power efficiency, reliability, and excellent signal/noise ratios in secure data transmission.
The modulation techniques developed for NTDS were formalized into industry standards for the “Tactical International Data Exchange”, and were eventually incorporated into commercial modems and internet protocols decades later.