One of my favourite computer history books is Stan Augarten's "Bit by Bit", which has an author-approved scanned copy at http://ds-wordpress.haverford.edu/bitbybit/

In it, the author makes the following assertion:

As a former military pilot, Tom Watson was quite familiar with radar and other avionic devices – the typical B-29 had about a thousand tubes – and he had a fine appreciation for the potential of electronic technology. Although Watson Senior and other old hands at the company believed that IBM’s customers would shy away from anything electronic, considering it too advanced and possibly unreliable, Watson decided to let his son test his hunch. ... To everyone’s surprise – including Tom’s – the entire lot was snapped up.

Allowing that bombsights and fire-control computers were still basically mechanical devices in 1946, should one assume that Watson Jr.'s enthusiasm was solely because he recognised that tubes (valves in UK English) could be reliable (and somebody in IBM had introduced him to the idea of digital electronics), or because the B-29 bomber contained digital equipment which has not so far been widely discussed?

  • I think it's just an observation that a system with hundreds of tubes could be reliable enough to perform a specific task, if engineered correctly. I do know there was a lot of work done on tube reliability during the war, so things like radar or navigation systems wouldn't fail.
    – RETRAC
    Oct 27, 2020 at 19:33

2 Answers 2


There is a significant step between mechanical (digital and analogue) devices, and digital electronics: Analogue electronic equipment. It appears that this is what the assertion is referring to. The B-29 contained a lot of electronic radio equipment: https://aafradio.org/flightdeck/b29.htm. Additionally there is the https://en.wikipedia.org/wiki/H2X radar and APN-9 LORAN radio navigation equipment.

Since digital equipment is built out of analogue electronics, the underlying technologies needed to get stable and cheap enough for building digital circuitry out of them to become practical.

  • Not really. Mechanical devices can be either, analogue or digital. IBM machinery was digital, so the transformation was from (electro)mechanical digital devices to electronic digital devices - no intermediate analogue step here.
    – Raffzahn
    Oct 27, 2020 at 10:21
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    @Raffzahn I think thats the point I'm trying to make. Electronic is an independent step from analogue vs digital, so seeing analogue electronics in the B-29, could inspire the use of digital electronics in refinements of IBM digital mechanical equipment. I've tried to edit the answer to clarify that. Oct 27, 2020 at 10:42
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    The link I gave has a bit more detail: it looks as though IBM had an internal design for an electronic multiplier, the SSEC project was ongoing, the Mark-1 was history but an interesting exercise, and there's a real possibility that Tom Watson was being a cheerleader for digital technology because he knew that analogue electronics was reliable. There's /also/ the possibility that the B-29 had something like beam-following navigation plus a /digital/ timer to control bomb release. Hence my question. Oct 27, 2020 at 10:46
  • @MarkMorganLloyd The B-29 had no need for beam following, because they had LORAN and a navigator, which didn't give away where they where going. Oct 27, 2020 at 10:57
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    OK, so they had LORAN. Is there any digital element in that, or was Watson's introduction to digital electronics entirely after he started working at IBM? Oct 27, 2020 at 11:09

I don't know about IBM, but in the UK, people like Maurice Wilkes gained wartime practical experience with electronics operating at megahertz frequencies and with delay-line storage, this latter being used to store one radar 'frame', so that background images could be screened out by subtracting one frame from the next.

As recounted in his memoirs, this gave Wilkes the knowledge and confidence to design and build the EDSAC, one of the first stored-program digital computers in service.

Digital techniques still had to be invented, but the underlying electronics technology was largely understood.

The relevance to Watson at IBM is, I suppose, that people grew sufficiently familiar with electronics technology to believe that complex systems could be built, and could be made sufficiently reliable that important work could be completed.

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    I think the delay-line reference is particularly interesting... I wonder whether the output was analogue or digital? I've used a (true) dual-beam 'scope with a beam delay which was presumably some form of delay line, and in fact very much wished I still had it when I was up against something a few months ago. Oct 27, 2020 at 11:36
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    The delays were analogue. Various techniques were used in that era to create delays for acoustic signals, using mercury, glass or twisting in metal wire. Transducers at each end converted back to electrical signals. The glass delay line was used in the PAL TV system until analogue TV was phased out. Oct 27, 2020 at 16:13
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    Too bad Turing's consideration of using gin as the storage medium for the ACE did not actually come to pass. The alcohol/water mix supposedly had good propagation properties at the required frequencies. Oct 27, 2020 at 19:21

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