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with the loss of only eleven. Another nine MiGs
had been destroyed on the ground as some of the
restrictions against hitting the jet-capable airfields
were lifted.
CO) In April and May, improved Air Force tactics,
equipment, and numbers of escort aircraft
increased the kill ratio to almost eight-to-one
over the North Vietnamese. Among the changes
was the introduction of the QRC-248 enemy IFF
transponder interrogator. The QRC-248 was
developed to read the SRO-2 transponder carried
on all versions of Soviet fighter aircraft.
Originally, it had been developed to target Cuban
and Soviet aircraft. In late December 1966, an
experimental EC-121 was dispatched to Southeast
Asia to see if the QRC-248 would work against
North Vietnamese aircraft. The test was successful.
The EC-121s could register the North
Vietnamese MiGs at a range of 175miles and now
could determine which radar returns in the area
(V) EC-121 College Eye
were MiGs. Since the SRO-2 transponder was
used by Hanoi's GCI to identify and control the
MiGs, it was expected that this technical feat
would be a breakthrough. QRC-248 sets were
sent to the EC-121D College Eye aircraft.
CD) At first, the effects of the QRC-248 were
limited. This was due largely to the requirements
of NSA in keeping the fact of its effectiveness
from the North Vietnamese. So, the operators on
board the College Eye aircraft were prohibited
from actively interrogating each radar return for
fear that this would tip off the GCI controllers.
Instead, the Air Force operators only passively
read the IFF interrogations initiated by the North
Vietnamese controllers. This lowered the number
of identities registered and the continuity on each
enemy track. In late July, the restrictions on the
use of the QRC-248 were lifted by NSA and the
JCS. The overall result of the wide-open use of the
system was that, for the first time, it gave intelligence
analysts and commanders an accurate picture
of MiG operations; it showed where their
standard orbits were and gave a more accurate
count of enemy aircraft. So complete was the picture,
that some observers found it almost frightening
when they realized how poor their previous
idea ofthe MiG threat had been. 5 9
(5//5I) In August 1967 another element was
brought into the support of air operations when
the EC-121K, the SAC Rivet Top aircraft, was
introduced into Southeast Asia. Rivet Top was
intended to function as an airborne extension of
the TACC-NS on Monkey Mountain. What made
Rivet Top exceptional was that it carried
COMINT positions, an enemy IFF display (based
on the QRC-248), and an ELINT display panel for
Vietnamese SA-2 radar, the Fan Song, all to provide
threat warning to American aircraft.
However, some of the functions were done poorly:
the electronic display of Fan Song returns
showed only a small percentage of the active
plots. The COMINT positions were controlled by
the Security Service and NSA; the rest of the crew
often was not cleared for SIGINT. Still, the general
success of Rivet Top was obvious to PACAFand
7th Air Force commanders. Of the twenty MiG
kills registered by the Air Force from August 1967
until the end of Rolling Thunder, thirteen were
attributed to Rivet Top. American pilots felt that
finally they had a decent GCI control.60
Originally, the aircraft had been dispatched for
only a 120-day test, but the Air Force chief of staff
ordered it to remain in the area until another suitable
replacement platform could be found. Rivet
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