Well, Hue is right in a sense. But the ARB was intended to replace the RU as the whole Megillah of the moment - liaison and/or command receiver. Of course, that was in the time when the specialization movement began in earnest. By the end of the war, you had specialized liaison, command, automatic compass, landing, and what-all receivers going into aircraft. The ARB was certainly the equal of the BC-348 performance-wise, but for hams it is a lot clumsier to use from the user-friendly perspective, and as a general search receiver, its RU procedural roots are less than stellar. I think that is why is rates lower on the scale these days.

Contrasting opinions are encouraged.

- Mike KC4TOS

On 10/28/2022 8:44 PM, Hubert Miller wrote:

You're thinking of the ARB + ATB, which was the pilot's Command radio. 
The radioman for CW position reports and so on, was GO + RU.  
I do not know for sure what Command sets were used when some of the PBYs were given instead BC-348 and ATC for liaison radio. 
-Hue Miller