Dan Cross &lt;crossd(a)gmail.com&gt; writes: The 1704689 flip-flop PCB is a Bendix part: https://www.ebay.com/itm/263975518840 This page has a picture of a "Nistri-Bendix AP/3 analytical stereoplotter (a special purpose instrument primarily used to compile contour maps and terrain profiles)", which sounds like the kind of thing the Air Force would have: https://www.cia.gov/library/center-for-the-study-of-intelligence/kent-csi/v… There's more information online about the AP/1, AP/2 etc., which consist of a digital computer driving some specalised plotting hardware -- so it sounds like the letter's talking about spares for the computer part of the AP/3. Whether that's the same as the AP-3 you're after, though... -- Adam Sampson &lt;ats(a)offog.org&gt; <http://offog.org/>

Wow — wonderful Dan, thanks for this! And prospective thanks to anyone else for their thoughts… Warm (in machine room) regards, Dag On Dec 20, 2019, at 12:49 AM, Dan Cross <crossd@gmail.com<mailto:crossd@gmail.com>> wrote: On Wed, Dec 18, 2019 at 1:52 PM Paul McJones <paul@mcjones.org<mailto:paul@mcjones.org>> wrote: Computer History Museum curator Dag Spicer passed along a question from former CHM curator Alex Bochannek that I thought someone on this list might be able to answer. The paper "The M4 Macro Processor” by Kernighan and Ritchie says: Alex and Dag would like to learn more about this AP-3 minicomputer — can anyone help? [I recommend that follow-ups go to coff, which is Cc'ed here] I took a short stab at this, but can find little beyond references in the aforementioned M4 paper. I did, however, run across this: https://www.cia.gov/library/readingroom/document/cia-rdp78b04770a0001001100… This appears to be a declassified letter written to the US Air Force at Bowling Green Air Force Base in regards to spare parts fo the AP-3 computer; dated October 19, 1966. The list of parts seem reasonable for a minicomputer, and it further seems reasonable to believe that this may be related to the same type of computer referenced in the M4 paper. However, details of the sending party have been redacted, and there is nothing pointing to the identity of the manufacturer. Sadly, that's all that seems available. I wonder if, perhaps, Doug McIlroy (Cc'ed directly to float this to the top of his stack) can shed more light on the topic? - Dan C.