[Milsurplus] If You're Interested in AAC PTO Radio Operators:

[David Stinson]

Outstanding web reference if you're interested in how
the Army Radio Operators did their jobs,
from the perspective of a Communications Officer in the Pacific Theater.
Not much on specific equipment, but still great stuff:

http://www.ibiblio.org/hyperwar/AAF/Biak/index.html

Here's an August 1944 passage,
including a reference to SCR-274N in B-25s, pp. 47:

Near the end of the war, replacement planes came in with Loran (long range 
navigation) radios.
They were an immense improvement over the old radio compass.
On the way to the target for the day there was to be no radio transmitter 
operating; even the IFF was turned off.
This was an attempt to prevent the Japs from knowing a few friendly bombs 
and a little hot lead was coming.
The pilots had three Command set radios tuned to three separate frequencies. 
These were for close air to air communications in bad weather and over the 
target on missions, to assist in take-off and landing instructions, and to 
help crippled planes in getting back to airstrip.
Everyone in the crew wore a throat mike and headset; these were plugged into 
the intercom system. By pressing a switch and calling a crew member's name 
on the intercom, you could contact any member of the crew if they were 
wearing their headset. Throat mikes were very very poor transmitters.
The IFF (Identification Friend or Foe) radio sent a signal to any U.S. 
airstrip that this was a friendly plane. Thus, a Jap plane with no IFF 
triggered a red alert when they approached one of our airstrips at night. 
There was an explosive charge in each set under the radio operator's seat, 
so that if a plane crashed in enemy territory, the IFF radio components 
would be destroyed and not compromised. Many a red alert was triggered 
because the radio operator forgot to turn on the IFF when approaching a 
friendly airstrip. You can guess, the IFF charges went off sometimes in 
maintenance and other periods when they weren't supposed to.
The radio operator and his receiver-transmitter were placed in B-25s for 
long range communications. In very good weather with the trailwire antenna 
down beneath the plane, the radio operator was able to transmit his Morse 
Code over a thousand miles. A different card was carried everyday for 
encoding messages; in an emergency such as wounded aboard, airplane engine 
problems, or threat of ditching, the Morse Code was sent in the 'clear'. The 
499th communications ground station was located next to the communications 
office, so if a plane had gone in over the target, a plane was in trouble, 
or a routine mission report on the way home--we were the first to get the 
news. Usually a Cat (Catalina flying boat) was part way to the target during 
a mission, so a radio operator could call them directly, if a plane was 
going to ditch. Many men survived