I've pondered that same question, Jack - back when Ray Mote K5FKT wrote his monographs on military nomenclature of aircraft equipment. 

Part of the question seemed to be unexplained, illogical dates of specific nomenclature designation, and the other part seemed to be specific aircraft usage.  

The designation date problem runs the gamut.  For a contractor to have a proposed product designated was one thing.  To have a military contract to make large numbers of them is quite another.  Witness the AN/ARC-21 transmitter was originally "designated" in 1944, but a contract to produce the RT-128(XA)/ARC-21 in quantity wasn't reflected in a document until the JANAP 161 in June of 1952!  Reverse examples like the AN/ARC-4 just serve to muddy the waters in the opposite way. 

Now, "Never designated" examples of aircraft usage (like the Bendix TA-2* and TA-12*) appear to have been installed only in USAAF "ash and trash" logistics carriers, not U.S. combat aircraft.  But they were often given British military nomenclature, as reflected in the manuals.

For me, the bottom line was not to worry about it.  The numbers are what they are, and the military mind doesn't always make things logically clear in print (after spending most of my 40 year career in and around the DoD, I often reflect on the timelessness of that trait.) 🙂

- Mike  KC4TOS

On 8/3/2025 11:42 PM, Jack Antonio wrote:
The Navy used the WE-233 early on, and when the JAN designation system
came out around early 1943, they gave it the ARC-4 designation. All the
manuals I've seen carry both designations. IIRC, the AN/ARC-1 started
entering service sometime in 1943.

It was always curious to me, knowing the military bought commercial
off the shelf radios for usage, why some sets wound up with a military
designation, and others retained their civvy designation in service.

For example, the Bendix RTA-1B received the designation of
AN/ARC-9, but the Bendix TA-12 did not receive any military nomenclature
that I'm aware of.

Jack Antonio
WA7DIA

On 8/3/2025 10:01 PM, Ray Fantini via Milsurplus wrote:

the WE-233 was around first and the ARC-4 did not make it to the military until later?