Thanks for that video reference. I was aware of much of the history from past interest but I'd not seen that video previously nor had I seen all of that film footage in other WWII docos.

The more I read about US research developments during WWII the more I appreciate the tremendous effectiveness of the US's OSRD (Office of Scientific Research and Development)—the instigation of the Manhattan Project, the huge enhancement of RADAR by the MIT Rad Lab (https://en.wikipedia.org/wiki/MIT_Radiation_Laboratory), the proximity fuze and much other work (as here: https://www.loc.gov/rr/scitech/trs/trsosrd.html), owes a huge amount of success to its science administrator, Vannevar Bush. Whilst Bush is still known amongst technical cognoscenti, it seems to me he ought to be much better known amongst the broader public. Not only was he a top rate scientist and engineer but also a first-rate administrator who got things done. It's very rare that we get someone with such a wide understanding of physical phenomena and engineering expertise in addition to having excellent administrative skills and experience.

It seems to me historians ought to promote Bush up amongst the ranks of the key players who were responsible for the US/Allied victory in WWII. Of course, Bush had much help from other important notables such as Alfred Loomis, Fredrick Terman (father of Silicon Valley and author of one of my textbooks), Henry Stimson, (War Secretary) and many, many others. Nevertheless, there was something unique about this group of individuals which is pretty rare, just about everything they touched worked well and was on time to help the war effort (shame that team isn't around today).

We continue to see many documentaries about military action during the War but they almost never mention anything about the enormous 'backroom' effort made by many, many people and of the remarkable amount of coordination that was necessary between them—unfortunately, they are now mostly forgotten to history. We need to give much more credit to those who made this huge contribution to the War effort—those who not only developed reliable and effective prototypes of new weapons but also who ensured that these weapons were put into production quickly and manufactured in sufficient quantity to effect a successful outcome of the War. Seems to me that the broader historical record ought to be changed and updated to reflect these forgotten facts.

Back to proximity fuzes. I'm still amazed these devices worked as well as they did. To understand why I'm still trying to find out more about their design details. For instance, on the web there are any number of cutaway drawings of the Mark 53 VT fuze together with lots of general descriptions of its operation but I've not found a fully detailed drawing of its circuit (engineering drawings, etc.). Nor have I come across a detailed description of its theory of operation (only general outlines). Nor have I ever seen its detailed specifications.

From various reports of its development, many thousands of test firings were done so where are these test results now (it's hard to believe that they no longer exist)? For instance, what was the sensitivity of the device, that is, what is the nominal distance from an aircraft (of given size) for its thyratron to trigger? There has to be a nomogram of aircraft sizes (or types) versus trigger distances, as this information would have been a vital conclusion from the testing procedures (not to mention also being key operational parameters).

Similarly, there seems to be no detailed description of the dry battery (aka its energizer) which provides the 'delayed-start' power to the device (some published circuits show that it supplies 100 Volts needed to operate the vacuum tubes and this voltage is what we would expect for battery-powered tubes)—but there's nothing about the battery's chemistry or its actual physical construction). To achieve 100 Volts EMF, multiple cells would have had to be involved (joined in series), however this poses a problem and it's never explained. The breaking of a single ampule of electrolyte to start the battery needs more detailed explanation. After breaking, the ampule would have flooded the whole (single) battery compartment which contained the dry battery cells. However, individual cells can never reach more than a few volts each let alone 100 Volts using standard chemistry—electrode potentials forbid such high voltages: https://en.wikipedia.org/wiki/Standard_electrode_potential_(.... So with only one single battery compartment why didn't the electrolyte short out cells as the voltage tried to rise above the nominal voltage potential for a single-cell? (Clearly, the fact that the fuze worked meant that the battery also worked and supplied the high 100V, so some important information is still missing.)

Perhaps this information is readily available and it's just that I've somehow missed it. I can't see any reason for why parts of this information would be still classified after all these decades. Moreover, such info could no longer be classed as a security risk for the simple reason that there is no way that you could get the specialized components for, say, to manufacture a clandestine device (the ruggedized tubes alone were very special and are no longer made).

If anyone knows where this additional info can be found then I think many of us would be interested in seeing it.

__

FYI, here's an aside comment on the strength of normal commercial glass vacuum tubes and vacuum tube glass.

Years ago, I worked in a TV station and there was always ongoing banter and rivalry between the electronic staff (engineers and technicians) and the electrical staff (electricians). Electronics staff looked down on the electricians and considered them clowns, likewise they considered electronics people as overpaid professional wankers (the rivalry didn't descend into animosity, rather it was more like behavior seen between competing football teams). What exacerbated this rivalry was that the electricians had their own building some 20/30 meters from the main building, it not only housed their complete operations but also the station's emergency power source (an ex-WWII submarine diesel engine and a 3-ɸ alternator). In essence, as a group, the electricians were isolated from the rest of the staff which put them slightly apart.

Anyway, some of the more adventurous of the electronics staff (including yours truly) were always up to mischief and one of our inventions was our infamous Valve Gun (Tube Gun for you US-ers). Initially, its invention had nothing to do with the electricians but later we found it a devastatingly effective 'weapon' to use against them. It consisted of a CO2 fire extinguisher with a conical discharge nozzle, two lengths of plastic electrical conduit about 2m in length. One conduit had an internal diameter just sufficient to snugly (but not tightly) fit 7-pin vacuum tubes (6AU6, etc.), similarly the other was for 9-pin tubes (12AT7, etc.). To operate, place a vacuum tube into the conduit at the near (extinguisher) end with base/pins first, couple the conduit into the extinguisher's nozzle until it is a tight fit, aim and then pull the trigger. Not far from us was an old disused quarry that we used as a test firing range, tubes would leave the gun with such velocity that there was no way anyone could ever see them exit the conduit. They'd then immediately disappear many hundreds of meters off into the distance to eventually land somewhere at the bottom of the quarry.

The electricians' building's entrance was through a green wooden door that faced the electronics department and OB garage exit on the main building. Much to our amazement, tubes fired from the garage at the electrician's door would embed themselves in the wood up to the full length of their pins but they would rarely break (after this tortuous ordeal their glass envelopes remained intact and their getter deposits were still a shiny silvery colour which meant their vacuums were still OK). Their internal electrodes, however, would often collapse downward towards the tube's base (to the glass seal area where the pins exit). Surprisingly, the collapse of the internal structure was often limited to only the support wiring that connected the pins in the glass base to the electrodes, that is, top and bottom mica separators, cathode, grids and anode structures often remained intact without any noticeable damage or obvious physical distortion.

This turned out to be more than just stupid antics on our part in that we all were amazed at the G forces that these glass tubes could take before their glass envelopes would break. Unfortunately, we had no simple way of measuring the exit velocity of the tubes but I'd confidently say it was such that if one of those tubes hit one in a vulnerable part of one's body then one could easily have been killed. At that time I was unaware of the history of VT fuzes. If I'd known about them back then, then I'd have taken more interest in the tubes' exit velocity. (In hindsight, we had access to 931A photomultipliers and oscilloscopes, so with a little effort we could have timed the tubes' velocity over a known distance). Perhaps in some minor way our 'gun-tube' experiments add a modicum of weight to the accuracy of the VT fuze story (even if at the time we were oblivious of the fact).

Oh, the electricians: they were only day workers, so we carried out our nefarious work on evening shifts. Suffice to say, they were not amused when they'd arrive in the morning to find a dozen or two vacuum tubes embedded in their front door. They couldn't retaliate either, whilst they could have easily built the gun only we had carefully guarded access to the tube ammo. Incidentally, removing the tubes from the door turned out to be very difficult. They were embedded in the wood so very tightly that they could not be removed by just pulling on them by hand. To remove them we forced screwdrivers under their bases and this was difficult (there being no space between the glass and the door surface). When glass envelopes were broken it mainly happened at this time.