OTH-G is mainly used within the US DoD armed forces and within SACLANT and many NATO navies. The OTHG format is based on message text formats (MTFs) within the OPSPEC. Each MTF is based on an ordered series of sets from the appropriate set library. Each message must be constructed in accordance with the rules for the specific MTF, the sets used to compose the MTF, their supporting tables and entry lists, and the General Formatting Rules. Background The Operational Specification for the Over-The-Horizon GOLD (OS-OTG) (Rev C) Change 1 of 1 August 1998 provides a standardised method of transmitting selected data between OTH-T systems and OTH-T support systems. It is designed to be easily man readable.