The UNIVAC 1101, or ERA 1101, was a computer system designed by ERA and built by the Remington Rand corporation in the 1950s. It was never sold commercially. It was developed under Navy Project 13, which is 1101 in binary. The UNIVAC 1102 or ERA 1102 was designed by Engineering Research Associates for the United States Air Force. The 36-bit UNIVAC 1103 was introduced in 1953 and an upgraded version (UNIVAC 1103A) was released in 1956. This was the first commercial computer to use core memory instead of the Williams tube. The UNIVAC 1105 was the successor to the 1103A, and was introduced in 1958.