Circuit designations are characterized by a letter and number
code. The 21JS4 primary battle circuit, for example, is identified
as follows: the numerals 21 indicate the purpose of the circuit;
the letter J denotes sound power; the letters S means general
purpose (radar, sonar, and electronic countermeasures [ECM]
information); and the numeral 4 indicates a particular station in
the circuit. The same circuit in the auxiliary system is X21JS4.
All auxiliary and supplementary circuit designations are preceded
by the letter X. Supplementary circuits are easily identified as
such because they have no letter after the letter J.
What does the letter J mean in sound-powered circuit
How can you identify a supplementary circuit?
The following are some typical shipboard sound-powered
Captains battle circuit
Aircraft control circuit
Combat information center informa-
Surface search radar circuit
Sonar information circuit
Maneuvering and docking circuit
Engineering circuit (fuel and stability)
Ship-control bearing circuit
Radio and signals circuit