As best as I can figure out...
System numbers are assigned sequentially as requested -
e.g. AN/URC-31, AN/URC-32, AN/URC-33 might be from different services
(sometimes a set of numbers is requested for a family e.g. AN/SRT-14. AN/SRT-15. AN/SRT-16)

Unit numbers are also assigned sequentially as requested and if associated only with a particular system, given that as a suffix.
e.g. CV-731/URC (used in multiple systems) or C-4099/FRR-60 (used only in AN/FRR-60)
(sometimes a set of numbers is requested for a family e.g.AM-3295/FRR-60, AM-3296/FRR-60, etc.)

The real poop is MIL-STD-196
https://quicksearch.dla.mil/qsDocDetails.aspx?ident_number=35607
5.2 Requests for Nomenclature. Requests for nomenclature are submitted by the DCP to the DODCP on DD Form 61, Request for Nomenclature, electronically submitted through the automated database (JETDAS), HTTPS://TDAS7.apg.army.mil/JETDAS . An enrollment form must be obtained from the website or the DCP in order to gain access to JETDAS.

Nick England K4NYW
www.navy-radio.com


On Mon, Jul 28, 2025 at 4:49 PM Jim Whartenby via Milsurplus <milsurplus@mailman.qth.net> wrote:
It seems to me that the Joint Army Navy (JAN) equipment SYSTEM designation does not always square up with with the Unit that is part of a system.  The R-. T- or RT- numbers assigned to the major components seem to be assigned much later in the design process.  Is the SYSTEM number assigned when the contract is awarded?   But the R-, T- and RT- along with any control (C-) or power supply (DY- or PP-) UNIT numbers are assigned much later after the prototype meets the preliminary spec?  Is there a method to SYSTEM and UNIT number assignments or is it just kinda willy-nilly?  


Then there are the gaps in the SYSTEM number lists by Andreas Parsch.  Are these gaps the result of systems that never made it to production?  Case in point is the AN/ARC-26.  I found reference that this was assigned to a Collins Radio Navy contract in 1947 which was then cancelled in 1952.  Andreas lists it as a communication set for the AC-130 which didn't exist until the mid 1960's, AFAIK.


Jim


Logic: Method used to arrive at the wrong conclusion, with confidence.  Murphy
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