Piercing the Fog - Air Force Historical Studies Office

Tools of Air Intelligence
continued. American SIGINT units operated in North Africa and during Allied
operations in Sicily and Italy. As the strategic air war evolved, American
airborne Y intercept operations began in the fall of 1943 to give long-range
bomber formation commanders in the Mediterranean the benefit of immediate
intercepts of fighter pilots’ and controllers’ transmissions. By the winter of
1943-1944, under the press of the intensified Allied bombing campaign, a large
portion of German air defense operations occurred beyond the range of U.K.based
signals intercept stations. In January 1944 Eighth Air Force began
experiments with airborne radio intercept operations conducted by Britishtrained
American aircrew members. (American bomber forces striking German
targets from bases in the Mediterranean had begun limited airborne signals
interception the previous fall.) When American tactical air forces moved to the
continent in June 1944, they established mobile intercept facilities that were
linked to American fighter control centers.”’
Although ULTRA did not play a significant role in the planning and conduct
of American air operations over Europe proper until the late spring of 1943, Y
intelligence had immediate operational application from the very beginning of
Eighth Air Force operations. Strategic air operations relied on Y intelligence in
three areas: employment of fighter escorts, postmission analysis, and planning
for future missions. In the actual conduct of operational missions, SIGINT was
more important in the employment of escorting fighters than of the bomber
forces. Y intelligence enabled Eighth Air Force and VIII Bomber and Fighter
Command headquarters to monitor enemy reactions to bomber raids. Since the
attacking bombers maintained radio silence, commanders could follow their
forces by listening to the transmissions of the enemy’s air defense network. The
RAF’s Y-Service, responsible for collating all plain-language transmissions
intercepted by a fan of receiver sites located along the coast, passed pertinent
enemy voice radio traffic and call sign data to the American headquarters over
secure telephone lines. Stations at RAF Cheadle intercepted German Morse
code transmissions, decoded them, and forwarded information pertaining to
GAF intentions and actual interceptions of bomber formations. This information
often included enemy alert notices and takeoff orders. Intelligence from these
sources was usually received at AJAX-VIII Fighter Command-within five to
twenty minutes of the original enemy transmi~sion.’’~ While the bomber force
was out of escort range (which occurred frequently until the arrival of the P-5 1 s
in January 1944), little could be done with this situational intelligence during
the inbound portion of a raid. When limited navigational skills often caused
significant deviations from planned flight routes, the information gained from
the enemy via Y enabled more effective and accurate escort rendezvous with the
returning bombers. During late 1942 and 1943, when German fighters could
harass the bomber force all the way to the Channel coast, a successful
rendezvous could significantly reduce bomber losses.
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