TADIL-A/Link 11 is a secure half-duplex tactical data link used by NATO to exchange digital data. It was originally developed by a joint committee including members from the Royal Canadian Navy, US Navy and Royal Navy to pass accurate targeting information between ships. The final standard was signed in Ottawa in November 1957, where the British proposed the name "TIDE" for "Tactical International Data Exchange". It was later made part of the NATO STANAG standardization process.
The system operates on two frequencies, one in the high frequency (HF) range for over-the-horizon (OTH) communications, and another in the ultra high frequency (UHF) range that uses much smaller antennas and is suitable for smaller ships but lacks the OTH performance. The system broadcasts packets of 30 bits length, with 6 bits of error correction and 24 bits of payload data. The payload is encrypted.
Link 14 was adopted at the same time as a low-end counterpart to Link 11. Link 14 is essentially a digital teleprinter system lacking encryption and automation, intended for ships lacking the ability to use Link 11 data in an automated fashion.
The designation "Link 11" is derived from "Link II", the British designation using Roman numerals before NATO standardized on Arabic numerals. "Link I" was the data link used by the Comprehensive Display System.[1]