SIGSALY was used for encrypted high-level voice communications during World War II. The KO-6 voice coder was released in 1949 in limited quantities; it was a close approximation to the SIGSALY at 1200 bit/s. In 1953, KY-9 THESEUS[11] 1650 bit/s voice coder used solid state logic to reduce the weight to 565 pounds (256 kg) from SIGSALY's 55 tons, and in 1961 the HY-2 voice coder, a 16-channel 2400 bit/s system, weighted 100 pounds (45 kg) and was the last implementation of a channel vocoder in a secure speech system.[12]