GJB 1389A was the Chinese military standard that first placed electromagnetic compatibility requirements at system level, and its publication marked a change in how Chinese platform programmes approached the subject: rather than treating compatibility as a property to be verified at the end of a development, the standard required it to be designed in from the beginning through the definition of margins between the emission of each subsystem and the susceptibility of the others. It was issued at a time when the Chinese armed forces were introducing platforms with a much higher density of electronic systems than before, and it was applied across the aircraft, ship, vehicle and ground installation programmes of that period. The standard has since been succeeded by the edition that broadens the subject from compatibility to the wider electromagnetic environmental effects, and a specification citing this number should be read as referring to the earlier, narrower requirement.