[ARC5] Basic Question on Use of Command Sets (and Interphone Systems)

[Mike Morrow]

Bob,

>The command sets were only used by the pilots and co-pilots.

True, the use of the command set radio was intended for the pilots, but
WWII-era USAAF interphone systems were normally set up so that every
crew member could receive audio from and transmit mic audio to the
cammand set.  There's a very good reason for that...see below.

>Bombers had a intercom set in a case the same size as a ARC-5/SCR-274
>receiver.

You describe the very late-WWII AM-26/AIC, part of the AN/AIC-2.  But
only late aircraft like the new B-29A/B aircraft had that before war's
end.

>All crew members were on the intercom. But the Command Set was not on 
>the intercom.

True for post-WWII AN/AIC-2 interphones, but not for most WWII USAAF
WWII aircraft interphone systems.

Most USAAF WWII aircraft were equiped with the RC-36 interphone system,
typically with ten or more stations.  The amplifier was the BC-347-*,
with a single VT-99, and about the size of a paperback book.  It used
a small separate PE-86 dynamotor.  ANY or ALL of its stations could be
connected to the command set to hear command set receiver and modulator
sidetone audio, AND to key and modulate the command set.

The very justified reason for this was:

SCR-274-N operator manuals point out that the SCR-274-N can be used as
an emergency interphone system.  The pilot selects on the BC-451-A
control box a transmitter that is NOT installed.  All crew members
select COMMAND on the BC-366 or BC-1366 station boxes.  When any
crew member keys his mic, the signal is amplified by the modulator
and distributed as sidetone audio to all stations selected to the
command set.

This would work even if an installed transmitter was selected, except
RF transmission would also take place.

This would work even if some other command set were used (like a SCR-522-A)
because transmissions made on the command set caused sidetone audio to be
placed on the interphone COMMAND audio bus.  (But there's no way to NOT
transmit RF as well for these sets.)

The SCR-274-N backup to the RC-36 interphone must have been of some value.
The RC-36 has absolutely no redundancy, and is not single-failure tolerant.

Doubtless the aircraft on which you served had been equiped with or modified
for the AN/AIC-2 or later.  

BTW, thanks for your service in the Korean War.  Korean War vets are the USA's
most ignored, forgotten, and unappreciated.

Mike / KK5F