There is only one real reason for the late introduction of the BC-946-B receiver to the SCR-274-N.  It was to support operation of the R-1/ARR-1 VHF (246 MHz) "ZB" Homing Adapter.  R-1/ARR-1 is the JAN nomenclature that was assigned to the USN's ZB-2 or -3 Homing Adapter.  Some R-1/ARR-1 adapters have name plates with USN contract numbers and others with Signal Corps Contract numbers.

 

The USN's version of this broadcast receiver is the R-24/ARC-5, intended for use with the AN/ARR-1 homing adapter or  potentially as MF Localizer receiver for the USN's AN/ARN-9 Air-Trak ILS (abandoned by 1944 in favor of the USAAF's superior ILS AN/ARN-5 UHF Glide Slope Receiver and RC-103-A VHF Localizer Receiver.)

 

With appropriate inter-connector wiring the AN/ARR-1 may be connected and used with the BC-946-B without need of the AN/ARR-1 control box or antenna switch.

 

The AN/ARR-1 was installed on some B-29 bombers, but its BCB output was fed to an AN/ARN-7 ADF receiver instead of a BC-946-B.

 

In fact, it is unlikely that the SCR-274-N and AN/ARC-5 sets were ever actually used with the AN/ARR-1.  The R-4*/ARR-2 Homing Receiver fit in AN/ARC-5 racks and eliminated need for both the R-24/ARC-5 and the R-1/ARR-1.  That's why surplused inventory of these items have almost always  been new unused condition.  OTOH, the USN's earlier ARA broadcast band receiver CBY- and CCT-46145 plus ZB-2 or -3 VHF Homing Adapters stand a good chance of having actually served in ARA/ATA command sets on carrier-based aircraft prior to introduction of the later AN/ARR-2 in AN/ARC-5 receiver racks.

 

Mike / KK5F