[ARC5] IFF Sets

[Mike Morrow]

Jeep wrote:

> ...the current system for MIL is pretty much the same, with Mode 2/B
> being the mil only discreet codes for air defense uses.  The Civil
> Mode A (mode 1)  and C (mode 3) are used, with mode C including your
> altitude info (via an encoder).

Then in the 1960s, the military added Mode 4.  The late Vietnam-era AN/APX-72
included Mode 4, but a KIT-1A/TSEC encoding "computer" was required to be
attached.  The AN/APX-72 is doubtless flying still today...and swimming as
well.  My missile submarine used the AN/APX-72 as its IFF set for (very rare)
work with aircraft.  Its fuses were normally pulled to prevent unintended
transmission from the unit.  It got the Communications officer on my sub fired
when it was determined he had gotten one day ahead of where he should have
been in the daily destruction of the coding cards.

In my collections, I find the old RT-82/APX-6 to be a far more interesting
piece of hardware than the RT-859A/APX-72.  :-)

I also have the ABK-* IFF (a.k.a. the SCR-595-A) and the SCR-695-A IFF (a.k.a.
the ABF-*).  I'd like to find a complete (with original tubes) AN/APX-2
someday, as well as a AN/APX-44.

There was an interesting IFF set of a sort designed to add on to the AN/APQ-13
bombing radar on B-29s called the AN/APX-15.  It produced a warning display
when radar return that was characteristic of the propellars of certain classes
of Japanese aircraft was detected.  I don't know if any were ever deployed.

Mike / KK5F