[ARC5] ARC-5/SCR-274 Navigation Receivers?

[Mike Morrow]

Dave wrote:

> The Navy kept RDF capability because they might be flying
> into a strip on a barrier island of the coast of Brazil...

I don't think that the USN retained *any* interest in small
aircraft (fighter) RDF after the ZB was available.  For large
patrol aircraft certainly, but those would not be doing RDF
with a R-24/ARC-5 and DU or DW loop.

>To understand why the Army dropped the loop connections
>after moving beyond the SCR-183...

But, it was the Navy that dropped the loop connections that
were part of the RAV CBY-46102 and -46103, when they designed
the ARA using the CBY/CCT-46129 and -46145 "loopless" versions.
The SCR-274-N was simply a reduced ARA/ATA set whose components
were electrically identical to the equivalent components of the
Navy set except for AF impedance.  If the Navy had retained loop
connections for the ARA, I'd bet that the loop feature would
have been found on the USAAF's BC-453 and -946 as well.

I suspect that the most likely reason that the loop terminals and
switch returned to the R-24 was to enable an AN/ARR-1 to be
connected to the R-24 at the loop terminals.  This would allow 
the possibility of swapping the R-24 input from command set antenna
to AN/ARR-1 and back without using the RE-1/ARR-1 antenna switching
relay and associated control box.  The *only* reason that might have
value is if the R-24 were to be used with T-15, -16, -17/ARC-5 in a
communications mode, and thus the R-24 needed access to the command
antenna.  As it turned out, the AN/ARR-1 and R-24/ARC-5 combo were
made obsolete by the significantly improved AN/ARR-2.  Thus the
R-24's principal raison d'etre disappeared.

> Given the condition of most BC-946s and ZBs when they hit
> the surplus market, I don't think that system got installed
> very widely in the Army's aircraft.

I agree, but in a subsequent post I mention definite documentation
that the ZB was installed on B-29s.  Of course, it was actually the
AN/ARR-1, but the co-pilot's switch for it was marked "ZB".  Most
(but not all) of the AN/ARR-1 components one comes across today,
including the AT-5/ARR-1 antenna, seem to have been procured under
Army Signal Corps orders.

> I think that system was obsoleted by the AN/ARR-2 before it was
> ever uncrated...

I have never seen anything that indicates that the USAAF ever used
the AN/ARR-2, although it would have worked in SCR-274-N racks.  A
cable to the AN/ARR-2 control box would be required, and one section
of the SCR-274-N multiple receiver control box would remain abandoned
for use.  Not as nice as what the USN did with the C-38/ARC-5.

> As for the R-24 not seeing use- I'd disagree. I don't think a lot
> of them saw use, but they'd have a role.  Many of the second-tier
> and tertiary allies in places like South America and Africa were
> still equipped according to the 1920s Naval agreements and would
> have used this band both for communication and for RDF with 
> shore-base broadcast stations.

That use as a communications set is really the only circumstance
that would possibly require use of the T-15, -16, -17/ARC-5 and the
R-24/ARC-5.  I agree that was a potential use, but I still doubt
any wound up in such actual use because small aircraft carrying
only command set equipment would likely not be found in such
regions, unless accompanied by a carrier.

> You weren't going to find an A-N range or a "YG" transmitter
> in Columbia in 1943, but you could find "Radio los Mosquitos"
> on 712 KC to "home on."  You could also talk to a Columbian Navy
> unit on 600 KC, which would then clamp his key so you could find
> him and the possible U-Boat contact he was telling you about.

That's in the realm of possibilities I'll admit.  But I don't think
it was likely, because Navy aircraft in such regions overwhelmingly
would have been large patrol bomber aircraft like the PB4Y.  These
mostly were equiped with the excellent USAAF SCR-269 ADF for homing,
and a liaison station of some sort that provided a transmitter and
receiver for such frequencies.  There's really no justification for
the R-24 and T-15/16/17 on such aircraft for communications, nor the
R-24 with DU for homing.

If smaller aircraft (which would not carry ADF and liaison equipment)
were submitted for possible service in such regions, other questions arise:

(1)  How did these aircraft get into the area?  Most likely by carrier.
The AN/ARR-2 and signal from the YE/YG would remain the best navigation
system for getting to and from the desired location.
(2)  Who would manage that command set R-24, whose controls are all at
the pilot's hand (not at any rear-seat operator).  Who would manage
the DF loop without which DFing with the R-24 can not occur?  Pilot control
of the all-manual DU loop is certainly not possible in small aircraft.
It worked during the RU/GP/DU days (pre-ZB) only because there wasn't a
pilot-only operated command set on board.  All of the radio gear including
RU and DU were controlled by the rear-seat operator.

Mike / KK5F