[ARC5] The AN/APS-13 In Three Different Combat Roles

[Mike Morrow]

> When I visited the Hiroshima Memorial museum in Japan, I saw a 
> cylindrical transmitter ( about the size of a quart of milk)that stated 
> was used to trigger "Fat Boy". It appeared to be a vhf transmitter with 
> either a 4-65A or 3x-250 in the final.

That bears no similarity at all to the four units that were used.

It has already been pointed out that four AN/APS-13 units (RT-34/APS-13,
made by both RCA and GE) were used in the altitude radar triggering system.
The stock RT-34 operates around 450 MHz, 450 watts peak pulsed, from two small
6J6 tubes.  These four sets used in the triggering system had to be altered
in frequency of operation to prevent mutual interference.  The small antennas
seen on the bombs are AS-62/APS-13 units.

Here is a description of its use in the bomb trigger system:

  http://cryptome.org/nuke-fuze.htm

> Does this bear any relation to the Buzzbomb one?

No.  The AN/ART-19 is an HF RDF tracking device only.  The AN/APS-13 as deployed
on the weapons was a pulsed radar that triggered the weapon at about 1900
feet above ground.  Even modern nuclear weapon re-entry vehicles use a small 
altitude trigger radar.

> Would be interesting to see a diagram of it.

The schematic of the RT-34/APS-13 can be found at:

  http://www.nj7p.org/millist/sch/rt-34.gif

A few more details are at:

  http://www.nj7p.org/cgi-bin/millist2?mode=normal&name=AN/APS-13

A very nice description of the AN/APS-13, with operating manual extracts
and photos, is at:

  http://www.duxfordradiosociety.org/restoration/equip/aps13/aps13.html

This system, designed to trigger a bell and alarm light in the cockpit
if a large metal object was detected behind the aircraft, was short-lived
in WWII service on night fighters like the P-51 and P-61.  It was found
by the British that its emission could be used by German aircraft with the
FuG-227 radar detector system to locate any aircraft using the AN/APS-13.

The UK later re-deployed the system, but now configured to detect objects
in *front* of fighter aircraft, to aid their location of the Fi-103 (V-1)
targets: 

  http://www.hawkertempest.se/ElectronicWar.htm 

Anyone familiar with the 1950s-era military radio surplus scene will recall
that thousands of these were available surplus after WWII for dirt-cheap
prices (about $1 less tubes).  It is a small unit with a a small built-in
dynamotor...all similar to but smaller than the RT-7/APN-1 radar altimeter.
The last one I've bought actually did cost $1 27 years ago...but was in new
condition, with all tubes.  The advertisements in the ham magazines called
them "Tail-end Charlies".  I've always considered it an interesting set.

I doubt that there was very much to salvage from the eight AN/APS-13 sets
that were on those two atom weapons.  :-)

Mike / KK5F