- SCM - Set, Complete, Meteorological
- SCR - Set, Complete, Radio
- SCS - Set, Complete, System
There was also a huge number of two-letter designators for the components and accessories for all these units. Some were pretty obvious, AT indicated antennas, HS for headsets, LS for loudspeakers, GN indicated generators, BA indicated batteries. BC was less obvious, basic components like a receiver. But RD stood for switchboards and EE for telephones,
In 1943 still in the middle of WWI the military introduced an all new numbering schema. This was called the "Joint Electronics Type Designation System" aka the “Army-Navy System” or “AN System.” (It was not actually used by the navy.) It was later changed to JETDAS with the inexplicable addition of the word "automated." But thankfully they did not re-designate existing models. As time passed the new system was applied to new devices and as technology progressed those older units fell out of service.