[ARC5] Navy LM Use

[Geoff]

>> ...bring up the question again of why the USN included an LM
>> frequency meter with essentially every large aircraft radio
>> installation.
>
> I don't believe this is a valid observation.  No WWII-vintage
> USN transmitter or receiver system had the capability to be
> set on frequency accurately with the indications on the radio
> set itself until the ATC.  Most liaison transmitting systems
> of the era have a CFI input terminal that goes to the LM-*,
> the LM was integral to frequency adjustment.
>
> An accurate assessment of USN installations would simply be
> that *ALL* aircraft with a radio operator (and liaison system)
> always carried the LM-*.  Aircraft without a radio operator
> did not.  The only exception might be the large single-engine
> aircraft like the SBD, TBD, and the like, which had radio
> operator/gunners.  I don't know if an LM was always standard
> in such aircraft.
>
>> This continued postwar, with the Navy version of the C-119 having
>> an LM installed.
>
> That's an obscure citation...there were only about 90 total R4Q-1 and
> R4Q-2 aircraft built.  But nonetheless, an LM-* would indeed be on board,
> just like a SCR-211-* would be on board the C-119* that didn't have
> something like an AN/ARC-21 or later liaison set.
>
>> Of course the USAAF had the BC-221 and theoretically, at least,
>> the unit of issue was one with every B-17 and B-24 and perhaps
>> other aircraft as well...
>
> The statement I made above for the USN use of the LM-* applies to
> the USAAF and use of the SCR-211-*.  All aircraft with liaison
> sets and radio operators had the SCR-211-* on board.  USAAF radio
> sets were no more or less accurately set and maintained than their
> USN equivalents.
>
>> - but it is rarely seen in photographs.
>
> Which doesn't mean it wasn't there.  It most definitely was.
>
>> So why did the USN place such emphasis on having an LM freq
>> meter on board?  Were their radios more prone to getting off
>> frequency or was there some operational need...
>
> There is *no* difference between the USN use of the LM-* and the USAAF
> use of the SCR-221-* that exists to be explained.
>
> The real question about frequency meter use applies to both USN and USAAF
> installations.  The very first liaison transmitter that had a built-in
> accurate calibration frequency indicator (CFI) was the ATC.  Without
> *any* external frequency standard, the ATC (and T-47/ART-13) could be
> operator set at 5 or 10 kHz intervals, depending on frequency.  The 
> USAAF's
> T-47A/ART-13 was even better...it could be set to 1 kHz accuracy for the
> full 2 to 18.1 MHz range without use of any external frequency standard.
> Once the liaison transmitter is set, the liaison receiver is easily
> netted to the transmitter. (The USAAF did a better job of this with
> the NORMAL-MONITOR netting switch that was part of the AN/ARC-8.)
>
> There was little need for a frequency meter for liaison sets with
> the T-47 or T-47A.  There was none needed for the crystal-controlled
> commend sets like the USN AN/ARC-1 and -12 or the USAAF AN/ARC-3.
> Yet often a LM-* or SCR-221-* was still carried.
>
> The LM-* was even less important for the USN AN/ARC-25, which is the
> combo of the AN/ART-13 and the AN/ARR-15.  In this system, the AN/ARR-15
> receiver can easily be set to 1 kHz accuracy without external calibration.
> Yet, the LM-* often appeared even where the AN/ARC-25 was installed.
>
> In USAAF aircraft, the SCR-211-* disappeared as AN/ARC-21 HF sets replaced
> the AN/ARC-8.  In USN aircraft, the LM-* disappeared as the AN/ARC-25 was
> replaced by the AN/ARC-38.
>
> Mike / KK5F


Here is a P2V radio install in 1962, the LM is quite prominent.
http://www.hypertools.com/neptune.jpg

In the same year during the Bay of Pigs fiasco the P2V-7 carried the 
ARC-38A, ARC-94(Collins 618-S, 618-T respectively), ARR-41, plus crypto and 
a Mite TTY.

Carl