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Flightline Friday Extra: More Than Everything You Could Possibly Want to Know about APR-25/6 September 25, 2017

Posted by Tantumblogo in Admin, awesomeness, Flightline Friday, foolishness, fun, history, non squitur, silliness, Society, technology.

Early in the Vietnam War, partly due to amazingly poor planning, but even more due to unbelievably onerous targeting restrictions, US tactical aircraft started racking up heavy losses to North Vietnamese Surface to Air Missiles (SAMs).  The SAM in question was the SA-2, which had been known about half a decade at that point, the SA-2 having played a role in the shoot down of Francis Gary Powers’ U-2 in 1960.

Since the rules of engagement imposed by the Johnson-McNamara Administration forbade attacks on SAM sites under construction, or even possibly under construction, for fear of “accidentally” killing any Soviet “advisors” present and thus potentially escalating the war, US airmen had to wait until positive proof that a SAM site was operational before they could attack it.  The only positive proof accepted was their being attacked by that very SAM site.  Obviously this gave enormous initiative to the enemy, and made attacking SAM sites when they were most vulnerable impossible.

Defensive measures were needed, and needed quickly.  But how to defend against a radar guided flying robot whose only purpose in life was the kill you?  Fortunately, the problem was well understood. Indeed, specialist aircraft like intelligence gathering types had been equipped with limited numbers of what were then called radar homing and warning receivers (RHAW) for years.  SAC’s big bombers also carried radar warning and electronic countermeasures (ECM) gear of varying degrees of effectiveness, but much of this was far too large and heavy to fit into a tactical aircraft.

Fortunately, a small company in northern California, Applied Technologies, Inc, later part of Litton, now part of Northrop Grumman, came rushing to the rescue, in late 1965, with their “Vector IV” product.  Consisting of 4 roughly equally spaced radio frequency receivers and some very basic analog processing equipment, Vector IV entered service as the AN/APR-25/6.  This equipment was first fitted to specialist “Wild Weasel” SAM hunter aircraft, and later, to almost every tactical aircraft in theater – certainly, every one that went up North.  It was fairly effective, but became much more so when coupled with the North American “SEE SAMS” (clever) system, which added capability to discriminate targeting and launch radar signals from regular radar tracking signals.

The equipment worked pretty well, and losses were reduced.  The seesaw battle of the electronic wizards on both defense and offense continues to this day, but, generally speaking, since the APR-25/6, the US has held the upper hand (we think/hope – we haven’t been seriously tested in 25 years).

The video below is an actual training film for USAF aircrew in APR-25/6 operation and tactics.  It gets way down into the nitty gritty, discussing import of length and intensity of strobe, billboard notifications and their meaning, and the varying sounds the equipment picks up when illuminated by various kinds of search, tracking, and fire control radars (a radar is like any other radio frequency device, and thus its signals can be interpreted as a sound).  Techniques used to spoof APR-25/6 are also discussed.  Very interesting if you are a slavishly devoted geek like me, all others will probably find it mind-numbingly boring.

I post this mostly to keep a record of this highly esoteric material since this video was posted once before but pulled because someone asserted the data therein was still classified.  Of course, it is not.

A picture of what modern radar warning receiver (today’s term) displays looks like.  Gone is the analog signal intensity reading and guessing, replaced by digitally processed symbology indicating the type of threat, distance and bearing, with priority ranking, etc:



1. Mrs. Maureen Avila - September 25, 2017

Off topic;
Petition of support of the Filial Correction of Pope Francis..open to all
Catholics for signature.

Mrs. Maureen Avila - September 25, 2017
Tantumblogo - September 25, 2017

I was getting to it. Took a really long time to write that post.

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