A Young Airman’s Experience with the HN-1 Modem
By Jim Hartle
Though the HN-1 was not a piece of crypto equipment, it was near and dear to most Airmen going through the Air Force Crypto School at Lackland AFB in the mid 1960s.  The HN-1 was a one drawer modem device that could be set to work either send or receive but only one way at a time.  They were used in conjunction with the KG-13 to run some data circuits.

The basic course in 1965 consisted of electronic fundamentals, the HN-1 and then the KW-26 and the KG-13.  The HN-1 was used as a beginner piece of equipment to allow the trainees to “get some experience on real equipment”.  The instructor told us over and over that it was obsolete and “we would never see it in the field” - famous last words.

As enterprising young Crypto trained killers we all promptly forgot everything we learned about the HN-1 after we tested the block because, “we would never see it in the field”.   If I remember right we also went on our first leave after the HN-1 and then returned for the KW-26 and KG-13. After school I was assigned to Wheeler AFB Hawaii.  I was mis-shipped to Wheeler.  I was really supposed to go to Wheelus AFB, Libia, North Africa but that is a whole other story.

When I arrived the NCOIC, MSgt Tommy L. Holland, ask me if I was trained on the HN-1 and I told him I was, but that it was an obsolete piece of equipment and no longer in the field.  WRONG!  He said “there are four of them in the back room” and “you're the only one that has had any training on them”!  Further he went on to tell me that, one only worked in transmit, one in receive only, one worked both ways (sort of), and the fourth didn't work at all.  He then went on to explain that my upgrade to a 5 Level hinged on the repair of the all four units.  We were allowed to keep our training material about the HN-1 when we left Crypto School, because it was unclassified, and for some reason (maybe the providence of Divine intervention) I still had them.

At Wheeler the HN-1 was used on a half duplex Autodin circuit to Hickam AFB using a KG-13, HN-1 modems and a Cubic with a 026 card punch and reader.

The HN-1 was made up of miniaturized vacuum tubes much like the type on the KWR-37.  Some were plugged in but most were soldered to the circuit boards.   I started with  the dead one since I was scared to touch the only operational spare equipment.  It took me about three weeks of constant work to unsolder and test each tube that looked suspicious (no glow).  I replace dozens of them and finely got it to where I thought it was operational both send and receive.  All this time MSgt Holland would stick his pipe-clenching face around the corner, once a day, followed by his head and ask how it was going.  I told him just fine and kept testing tubes.

Since it was only a half duplex circuit, testing the modem was a long affair with begging for down time to cable them up and reset the circuit and test.  Upon completing the repairs on the first HN-1 and proving that I had a little bit of maintenance ability MSgt Holland was anxious to get all of them operational both send and receive and be able to call the complete system operational.  A total of six months elapsed before that goal was attained and literally 100s of vacuum tubes unsoldered, tested, and replaced and soldered back in.

When I was finished repairing the HN-1s, and had my CDC (Career Development Course) course finished, I was recommended to see the evaluation board for recommendation take my SKT (Skill Knowledge Test).  I passed the board took the SKT, passed it and got my 5 Level.  I learned a lesson and never again believed the phrase “You’ll never see this again”.


1) Jim Hartle  < Hartle1(at)

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Sept 14/10