[ARC5] Navy LM Use

[Robert Eleazer]

Dave's latest excellent pictures bring up the question again of why the USN included an LM frequency meter with essentially every large aircraft radio installation.  This continued postwar, with the Navy version of the C-119 having an LM installed.

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 - but it is rarely seen in photographs.  

Obviously, the BC-221 was battery powered, and with internal batteries, and thus more suitable for hauling around from aircraft to aircraft.  In fact, the only wartime picture of a BC-221 I have ever seen is on Guadalcanal, where a technician is standing in front of a P-400 Airacobra with a BC-221. The caption says that the "cheap" radios in the aircraft required a daily retuning to keep them on frequency.  It appears the radios were SCR-283.

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, such as the type of use of the radios?

Wayne