Vietnam era F-4s Q

Buzzer wrote:

On Fri, 08 Aug 2003 08:35:18 GMT, Guy Alcala
wrote:

In the 1 1/2 year period between the introduction in SEA of the
APS-107D and the APR-36/37 which would you have preferred? The APS-54,
Vector 4, pre-qual/qual APR-25/26 or APS-107D? Especially if you knew
the APS-107D detected missile launch the same way as the year and a
half in the future APR-36/37?

Bob, I thought they'd modified the APR-26 to look at the signal
characteristics instead of just the power level so as to cutdown on false
launch warnings (the NVN 'playing the L-band'), and that this was carried
over to the APR-37?

I don't know the history of the F-4C APR-26 after last quarter of
1967. I remember on the F-105 weasel the Bowman mod that tied the
launch into the APR-25 strobe pointing to the site. No memory of any
changes to the launch detect for the APR-26 on the F-105 in 1969 at
Korat. Seems like I would remember that since it would have been like
the APR-37 my primary system at that time.
The AS light on the APR-36/37 was the simple version of the ALR-31 on
the weasel which I think had been around for a couple years.

You're right and I was misremembering. It seems that APR-37 was essentially
the APR-26 with that modification, but that APR-26 itself wasn't improved.
Here's what I've got, from Jenkins' book on the Thud:

"The Air Force also conducted a quick look evaluation of a potential APR-26
replacement in April [1966]. An HRB-Singer 934-1B missile warning receiver
was installed in 62-4416 and test flown at the Sanders facility, which had a
Fan Song missile guidance simulator not available at Eglin. The 934-1B
differed from the APR-26 in that it analyzed the modulation characteristics of
the C-band [i.e. radar L-band] guidance signal to differentiate between SA-2
missile activity and missile launch modes, while the APR-26 simply looked for
an abrupt amplitude increase. The HRB-Singer set performed well, but the Air
Force was already committed to a large APR-26 procurement and saw no
compelling reason to buy another system to perform the same function. Only
after the Wild Weasel III F-105s were in combat was it learned that the
APR-26's design was based on possibly faulty intelligence regarding the
amplitude increase. This led to numerous incidents of flase lower
threat-level 'activity' indications when 'missile launch' should have been
displayed. The APR-26 was later modified to analyze the guidance signal and
the improved sets redesignated APR-37."

This was separate from the QRC-317 SEE-SAMS/QRC-317A ALR-31, which was
eventually incorporated into the APR-25 ('SPOT SAM') and turned it into the
APR-36 (the 'centered in both beams' A/S light). Jenkins, further on his his
section on the Weasels, also seems to mention the same mod you call the
'Bowman', although not by name. The description certainly fits:

"A separate modification provided the capability to correlate a C-band missile
guidance signal received by the APR-26 to a specific E-F band signal displayed
on the APR-25 azimuth indicator."

BTW, how was this displayed by the strobe? I've seen references elsewhere to
dashed versus solid lines or something similar, but nothing authoritative.

Guy