National Union made very good tubes and had a decent development shop. Hygrade-Sylvania might have been bigger and in some ways, superior, but NU was fairly clever, and sometimes beat RCA to market with new types. They made a lot of tubes for the war effort, second-sourcing RCA, of course...

I wholly disagree with their statement that the G-10 was developed in the 1930s, as RCA hadn't even yet developed the T-6-1/2 noval 9-pin base upon which the G-10 sits. (The noval was a postwar outgrowth of RCA's pioneering 7-pin-through glass (T5-1/2 bulb) design first developed just before the war for portable radios... The noval base was released in 1948 to accommodate more complex / multi-section tubes, and became an industry standard. NU was licensed to use it, of course) Accordingly, I place the G-10 no earlier than 1948, although it is likely that some flying-lead experimental devices might have been built a year or two earlier.

I've seen G-10s in the hands of other tube collectors, and own a couple of ancient INDITRON variants (NIB) called G1-045A, here. Both are marked "Research Division, NU", patents pending. The green, black and white box is likely late 1940s, and has handwritten type numbering. These displays are in T6-1/2 bottles on 10-pin bases, with no keying, just a yellow paint mark for the user to abide by when installing the tube. Easy to goof!

No center pin in these, like the G-10 has, but rather an exhaust tubulation is there instead. That makes me think the G1-045A was designed to avoid the side tubulation, but I've not been able to establish which tube came first. My guess is that mine are lab variants, designed to use conventional tube envelopes and manufacturing equipment, including rotary Sealex machines. These look like very elongated Nixie tubes, missing the front mesh, and having lots of painted on insulation on the internal wiring to the various cathanodes. Trouble is, they needed a special 10-pin socket, and I've never, ever seen any of those.

The pre-Haydu tube most often cited is the National Union GI-10, not G-10 (sic) as I'd written. Perhaps "GI" might mean "gas indicator". After going downstairs and finding the carton with little gas bottles, sure enough the ones I have might well be GI-054A, and not G1-045A, but that is difficult to say for sure. The stamped yellow ink isn't very clear, and that is understandable as these are certainly handmade toys from time when the earth was still flat.

The NU INDITRONs seem quite difficult to find. In 40 years I've only seen a half dozen or so, including the ones here. Mine came unsolicited in a heap of postwar tube cartons from the estate of a good friend who liked tube audio, old radios and musclecars. I am certain that he never even noticed them, much less cared what they were. Sadly, all the NU 2A3 and NU 50 boxes were empty...

Given the close knit tube-design community in this area, one might expect the Haydu Brothers were well acquainted with NU's designs, and improved by adding a front cathode mesh to make driving the numerals simpler. Haydu often took R&D products and productized them for others, including RCA, in an early form of outsourcing. Who knows what went on between NU, Haydu and Burroughs? Government (AEC) money may have been involved, but that is just conjecture that needs discussion within the Tube Collectors Assocation.

Also by 1952 or so NU was getting out of vacuum tubes to become more diversified, and I have no information regarding patent issues, but suspect that Haydu must have legitimately acquired some rights to the underlying design and manufacturing technology. (NU, in 1965 bought Emerson TV & Radio, who had previously acquired the DuMont name. All were fine area companies, and I knew people who worked at each of them.)

From the patent:

This invention relates to signaling devices and more specifically to glow lamp indicators for selectively signaling numerals, letters or other characters or symbols.

The patent describes the operation of the device:

In the well-known space discharge devices or glow lamps, a pair of metallic electrodes are sealed within a glass bulb filled with neon, mercury, sodium or other suitable gases at a definite very low pressure. When a unidirectional (direct current) potential is applied to the electtrodes and gradually increased, the glow discharge will set in at a certain definite potential called an "igniting potential." The luminous glow discharge is produced by negative electrons and positive gas ions and takes place within a certain small distance from the exposed surface of the cathode or negative electrode, which appears to be surrounded or coated with a thin film of light. This film of light follows the contours of the cathode surface in all details.

When the potential is further increased, thbe glow discharge becomes somewhat brighter. When the potential is gradually reduced, the glow discharge is maintained down to a potential considerably below the igniting potential, until at a certain definite minimum potential the discharge ceases.

If an intermediate potential somewhere between the igniting and minimum potential is applied to the electrodes, there will be no glow discharge, but if the potential is momentarily raised to or above the igniting potential and thereafter reduced to the intermediate potential, the discharge will be started by the igniting potential and thereafter be maintained by the intermediate potential until the potential is reduced to or below the minimum potential. This characteristic of the glow lamp makes it possible to control the starting and stopping of the glow discharge by means of brief momentary impulses of high and low potentials, with the lamp normally connected to an intermediate potential.

Thus, the glow lmap may be lighted by the application of an igniting impulse and thereafter remains lit, until the potential is reduced momentarily below the minimum potential. This feature offers a means to control glow lamps without external holding relays or other means for keeping the lamp circuit closed with it is desired to have the lamp glow.

The fact that the exposed parts of the cathode of a glow lamp are entirely surrounded by a thin film of luminous discharge may be utilized to display any desired character by means of properly shaped cathodes. A cathode consisting of a wire shaped in the form of the numeral 1 will, when ignited, produce a luminous outline of the numeral 1, and similarly any other desired character may be formed.

The patent also describes a stock quotation system using a coding scheme adapted to the use of these numeric gas discharge tubes as the display device.