During WW2, Prose Walker, W4BW, (then W2CXA) in 1942 became Chief of the
Radio Security Center (RSC) of FCC's RID, located in the Dillingham Building,
Honolulu. (Long after WW2 Walker was Chief of the Amateur Division of the FCC,
succeeded by John Johnston, W3BE, President of QCWA.) In his position as Chief
RSC Walker learned that many military aircraft and its personnel were being lost
at sea while traveling from the U.S. Mainland to Hawaii. There were two reasons
for their being lost, 1) 'navigationally impaired' pilots (bureaucratese for
'lost'), and 2) totally drained fuel tanks. There was naturally a limit to the
size of the fuel tanks, but what caused the pilots to become navigationally
impaired? That point preyed on Walker's mind, and on investigating he discovered
a deplorable situation that needed fixing. Here's what he found.
At the Boeing aircraft plant in Seattle they were building bombers as fast
as possible. Dozens of green flight teams just out of flight school were
awaiting their new aircraft, and anxious to get aboard and proceed to the South
Pacific area as soon as possible. The navigators and radio operators were taught
how to use the loop direction finders that were standard equipment on the
aircraft. But they were never told that loop DF's were incapable of obtaining
reliable directional information from signals propagated by sky waves. The DF's
aboard the aircraft were capable of delivering reliable data only when the
electromagnetic energy in the received signals is vertically polarized, but the
navigators and radio ops didn't know that. Unfortunately for them, on reflection
and refraction through the ionosphere, a linearly-polarized wave is converted
into an elliptically-polarized wave, resulting in a continual shift in the null
obtained by the loop DF as the polarization angle of the incoming signal rotates
elliptically during propagation. Consequently, once the aircraft has left the
mainland, and can no longer receive the vertically polarized waves from AM
broadcast stations, the only reception remaining is from sky waves propagated
far beyond the range of the ground waves of the AM stations. Therefore, bearings
taken from the loop DF's aboard the aircraft when at sea beyond the ground wave
signal were useless. The only remaining means for the navigator to determine the
position of the aircraft was through celestial navigation, using readings from
the sun or stars. The situation gets pretty bad on cloudy days, and that's when
the pilots became navigationally impaired.
At this point Walker came up with a solution that ended the era of lost
aircraft flying between the mainland and Hawaii. Fortunately, every FCC
monitoring station in the U.S., Hawaii, Alaska, and Puerto Rico had Adcock
direction finders as standard equipment. Adcocks, as you probably already know,
are susceptible only to the vertical component of the arriving wave, regardless
of its angle of polarization. Therefore, instead of constantly wandering, as
with the loop DF, the null obtained appears at constant angle on the Adcock
scale, even though the angle of polarization of the arriving wave is continually
rotating elliptically. In other words, Adcocks give accurate directional
information obtained from sky waves. Walker's reasoning was that triangulation
from bearing measurements obtained by the FCC Adcocks taken on signals
transmitted from the lost aircraft could determine its precise location, and
thus determine a course to fly directly toward Hickam Field in Honolulu. The
problem then was how to organize the communications to achieve the necessary
procedure. Walker organized it in this manner:
The CAA (then the Civil Aeronautics Administration) had a terminal in
Honolulu with facilities for communicating with all aircraft. A direct teletype
connection was setup between the CAA and the RSC, which had a kilowatt
transmitter used to communicate with the secondary monitoring stations on all
the Islands, each of which had Hallicrafters HT-9 transmitters. When the pilot
of the aircraft determined they were lost, the radio operator signals the CAA,
who instantly puts the aircraft's frequency on the teletype and rang its bell,
alerting the RSC operator of the situation. The RSC operator then sends the
following message to all secondary stations that continuously monitor the RSC
frequency: "LOS LOS LOS 4250 4250 4250," where LOS meant lost aircraft and 4250
was the frequency being transmitted by the aircraft. The operators of the Adcock
DF stations immediately tune to the 4250 KHz frequency, hears the aircraft, and
begins taking continuous bearings. The aircraft is sending long dashes, MO MO
MO, to enable the DF operators to be certain they're hearing the right signal,
and obtain a satisfactory bearing angle on a moderately constant signal.
As each bearing is taken by all stations, the bearing angles are
transmitted to RSC, where a great circle map of the entire Hawaiian area is
hanging on the wall. A compass rose is printed on the map at the location of
every monitoring station in the Islands, with a hole in the center of the rose
through which a weighted string is hung. A pin is attached to the opposite end
of the string to secure the string at the desired point on the map, with the
string stretched over the angle on the compass rose indicating the angle of the
bearing obtained by that particular station. As the strings representing each
station reporting are secured they intersect at the point indicating the
location of the lost aircraft, the intersection point called a 'cocked hat'. It
was usual for the aircraft's position to be determined within ten minutes after
the pilot alerted the CAA of its being lost.
After the aircraft's position is located it is then given a course to fly
toward Hickam Field, and the bearing measurements are reported continually until
the pilot can see the Field. During this time the aircraft's location is
followed all the way in to the Field, thus verifying the accuracy of the bearing
measurements and the pilot's success in following the directions.
Once Walker's plan was in operation no more aircraft were lost while flying
between the mainland and the Hawaiian Islands. In 1943 alone, 273 aircraft were
saved by the FCC Adcocks, and more than 600 were saved during the duration of
the War.
Unfortunately, planes were continuing to be lost on the run between Hawaii
and the South Pacific, so Walker was invited by the Military to investigate.
What he found was almost unbelievable. The Army Air Corps was using Mercator
Projection maps for those runs, unaware that using maps of that projection
produced directional errors of humongous and fatal proportions. On Walker's
advice, once they acquired new maps with great circle projection, the number of
lost planes dropped to zero.
This is just one of the stories of how the FCC assisted in the ending of
WW2. I was privilged to have been one of the bearing takers.

Walt, W2DU