Could proximity fuses have halted the bomber offensive against Germany in 1944?

[J.A.W.]

From the curious proximity fuse application dept:

Chris Thomas in 'Typhoon & Tempest Aces of WW 2' - on P. 56 notes that during anti-V1/cruise-missile ops:

"Australian John Horne, attempted to catch one while still carrying his rockets after an uneventful anti-shipping
reconnaissance. Unable to close to effective cannon range, Horne lifted the nose of his Typhoon & launched
4 pairs of rockets at his tiny quarry. At least one of the impromptu weapons hit the 'buzz-bomb', which broke
up & spun down into a field.

This led to the rapid trial of 'Z-battery' AA rockets, complete with proximity fuses, in place of the
standard rockets. & although successful on one occasion, the device was not adopted."


So, an early example of advanced hit-probability air-to-air missile interception tech, which no doubt, the LW
would've liked to have available in mid `44, too..

Edit: Corrected typos.

 

[basil]

I have to say that Koopernic's post #79 of this blog is the first detailed description of a German AA artillery VT fuze I have read in the literature or in the net. Until now most of the sources I have seen just rely on a vanished (?) CIOS report mentioning Kuhglöckchen as electrostatic influence fuze without technical details. Even Fritz Trenkle does not tell anything about it in his books.

Unfortunately Koopernic does not seem to be active in this forum anymore. Does anybody know more about the original source of his description?

 

[bbear]

I have to say that Koopernic's post #79 of this blog is the first detailed description of a German AA artillery VT fuze I have read in the literature or in the net. Until now most of the sources I have seen just rely on a vanished (?) CIOS report mentioning Kuhglöckchen as electrostatic influence fuze without technical details. Even Fritz Trenkle does not tell anything about it in his books.

Unfortunately Koopernic does not seem to be active in this forum anymore. Does anybody know more about the original source of his description?

Hi, I found 1 reference to the fuze developed by Rheinmettal Borsig as described by Koopernic on line, it gives two sources. The piece seems to be copied to many sites.
Proximity_fuze : definition of Proximity_fuze and synonyms of Proximity_fuze (English)

1. ^ Truth About the Wunderwaffen by Igor Witowski
2. ^ CIOS report ITEM no 3 file no XXVI -1 (1945)

I have to be honest, the first source reviews in amazon give me the impression that the source is detailed but unreliable. The second is the source which if I remember correctly contains both successful and unsuccessful innovations. And the specific file is not mentioned in popular online lists.

Early posts on this thread up to 7 raise the possibility that this is a hoax and Greg P the only one of us with relevant experience can't understand how an electrostatic fuze could work.

Even given the additional details, nor can I. From altitude both shel and aircraft would have he same electrostatic charge at say 30,000 feet it's about 10kV I think, because of the ionosphere. The shell is moving that much faster, an aircraft can accumulate 1MV I'm told. So call the maximum charge difference from aircraft to shell as 1MV. Moreover the rotating wire in a field I would expect to also radiate a 300Hz wave if there were any current detected, but where would such a current come from? Rotating a wire in a static electrical field produces nothing? V field, but no H field, 'cos Static? What would induce electrons in the antenna to move (current). At any instant the whole antenna would be at the same voltage? I think all you can have is a sensitive electrometer.


Of course I could be quite wrong. Often am.

 

[fliger747]

The appearance of a German Proximity fuse would have of course created a dramatic emphasis on countermeasures. Jamming and fooling the Fritz X guided bomb occurred quite quickly, as did counter emphasis on the more vulnerable mother craft. Likewise the Japanese "guided" flying bomb was most vulnerable when being carried by its launching ship.

Certainly flak batteries could be quite susceptible to suppression, fighter sweeps, VT bombs and whatnot. The component train in tech projects is also quite susceptible to disruption. Perhaps if developed earlier in the war, but later on the tide of history was like all tides.

 

[Shortround6]

I believe the Americans and British were working in counter measures to the proximity fuse within a few months of developing the first successful ones. Just in case the Germans or Japanese did develop something similar.

 

[fliger747]

Yes I saw some reference to countermeasure development. Makes sense!

 

[Shortround6]

it was rather easy to do, the hard part is figuring out what frequency the fuses operate on.

 

[Zipper730]

The question I have is: If we had proximity fuses that could take such enormous g-loads, and some were fitted to rockets -- why did we have so many guidance system failures during Vietnam?

Most were caused by the following

• Dropping: Sometimes, when the missiles were put on the wings, or fuselage of the aircraft, they'd drop off and hit the ground. In cases where the missile didn't have any denting or damage to fins or shape, they would often just send the plane on it's way. I'm not sure what g-load a missile hitting the ground after dropping a few feet off an aircraft's wing or fuselage would be, but it seems quite a lot less than 5,000-8,500g on the low end to up to 20,000g on the upper end of things. I've fallen about 10-20 feet, and I figure if I had been subjected to these g-loads, I'd be mist.
• Jarring: Basically, the missiles were often carried on trucks that lacked shock-absorbers. The fact that the testing facilities were not on the base, and sometimes located at separate facilities, where they would have to travel across bumpy roads, and things of that sort. To make it worse, air-bases often had these washboard structures meant to shake off FOD.
• Temperature: The missiles at sea-level were in warm/hot weather, and temperatures that were -20F to -70F at around 15000 to 40000 feet where you'd typically see fighter planes operating within. The result of temperature is contraction and expansion, and different components expand/contract at different rates. As a result, sometimes missiles would pass electronic inspection, then fail spectacularly in the air.
• Corrosion: The air in Vietnam was hot and moist, which can accelerate corrosion on aircraft operating with the USAF and USMC; the USN operated off carriers in the salty-air at sea. I'm not sure what the protocols for missile assembly were, but I'm curious if the missiles in either case were left partly assembled in the open.

I'm curious how these conditions would compare to conditions in territory that was controlled by the United States itself. I assume our test-facilities were on the base themselves, with air-temperature and humidity varying with location. I'm not sure how TAC & SAC varied in terms of maintenance -- SAC generally was more anal about things being done exactly right, but I'm curious if mistakes were made.

 

[Shortround6]

Proximity fuse was a very simple device as electronics goes. One the biggest headaches was getting a battery that worked after being in storage for up to year or more and still work like a round of ammunition. No testing or check out before firing. Ordinary dry cells (flashlight batteries ) of the time could not do this (hold a charge that long). Developing a wet battery where the acid was stored separate and would flow into the plates and start working in a fraction of second was as much of a technical achievement as the rest of the fuse. So was producing the fuse and batteries by the hundreds of thousands if not millions.
Even a simple guided missile uses at least an order of magnitude more parts than a proximity fuse and probably several orders of magnitude and that is where the reliability went.
Each part/component in the guidance system has to be an order of magnitude more reliable than the parts in the proximity fuse.

 

[fliger747]

I was curious about the tube technology used in VT fuses. Apparently they did various ruses in design by orienting the parts structurally and filling the tubes with wax! A lot of genius in design, persistence and technical capability expended here! It was done by never say impossible types!

 

[Zipper730]

I was curious about the tube technology used in VT fuses. Apparently they did various ruses in design by orienting the parts structurally and filling the tubes with wax!

When you say "orienting the parts structurally" you mean putting the strongest parts in the places where the most strength is required?

I guess the wax is there because it's soft and, for most purposes (it seems) shock-absorbant?

 

[ThomasP]

I once read that the solution for the G shock the British developed (before the Tizzard Mission) was to pot(?) the circuit in a specially developed wax-like substance. When the gun fired the pressure from the acceleration caused the substance to transition from plastic to fluid, allowing the circuit to move backwards a small distance in the projectile, while the plastic-fluid material absorbed the axial shock, and supported the tube(s?) from all directions. The article went on to say that the US and UK thought it would be better for the US to finish development of the finer/final details of the VT fuze, primarily due to a shortage of resources for production, but also for security concerns. The production capacity was an obvious problem, but the British also felt that just getting ready for production would be entail so much activity that it would be difficult to achieve without alerting the Germans. The British ran a pretty secure game during the war, but at the time they could not be sure of it.

Interesting fact, the British turned over their research on fission during the Tizzard Mission also, for the same reasons as for the VT fuze. The information included their theoretical research into fission (some of which would be useful in the development of the A-bomb) AND their design theory for a nuclear reactor for electric power production. I am sure you are all aware of the US Manhattan Project, started in 1939 (before the Tizzard Mission of 1940), but I had not been aware of the amount of info the British supplied the US, or of the research into a nuclear reactor for purposes of generating electric power. Some of the design theory for a nuclear reactor was used for the Manhattan Project, and was apparently the basis for the first post-war reactors built by the US and UK. The source of this general info was 'A Short Essay on the United Kingdom's Contribution to Nuclear Power", delivered as a hand-out in 1960 to the House of Lords and House of Commons. Apparently there was a crisis involving funding further research and development of nuclear power.

 

[fliger747]

The references to the structural integrity of the parts was rather vague, but indicated structural orientation to survive high G loadings along the axis of the shell and loads from the not inconsiderable rotational forces generated.

 

[Shortround6]

loads from the not inconsiderable rotational forces generated.

A masterpiece of understatement. A US Navy 5in AA shell could easily hit 1000rps or 60,000RPM.

 

[tyrodtom]

The question I have is: If we had proximity fuses that could take such enormous g-loads, and some were fitted to rockets -- why did we have so many guidance system failures during Vietnam?

Most were caused by the following

• Dropping: Sometimes, when the missiles were put on the wings, or fuselage of the aircraft, they'd drop off and hit the ground. In cases where the missile didn't have any denting or damage to fins or shape, they would often just send the plane on it's way. I'm not sure what g-load a missile hitting the ground after dropping a few feet off an aircraft's wing or fuselage would be, but it seems quite a lot less than 5,000-8,500g on the low end to up to 20,000g on the upper end of things. I've fallen about 10-20 feet, and I figure if I had been subjected to these g-loads, I'd be mist.
• Jarring: Basically, the missiles were often carried on trucks that lacked shock-absorbers. The fact that the testing facilities were not on the base, and sometimes located at separate facilities, where they would have to travel across bumpy roads, and things of that sort. To make it worse, air-bases often had these washboard structures meant to shake off FOD.
• Temperature: The missiles at sea-level were in warm/hot weather, and temperatures that were -20F to -70F at around 15000 to 40000 feet where you'd typically see fighter planes operating within. The result of temperature is contraction and expansion, and different components expand/contract at different rates. As a result, sometimes missiles would pass electronic inspection, then fail spectacularly in the air.
• Corrosion: The air in Vietnam was hot and moist, which can accelerate corrosion on aircraft operating with the USAF and USMC; the USN operated off carriers in the salty-air at sea. I'm not sure what the protocols for missile assembly were, but I'm curious if the missiles in either case were left partly assembled in the open.

I'm curious how these conditions would compare to conditions in territory that was controlled by the United States itself. I assume our test-facilities were on the base themselves, with air-temperature and humidity varying with location. I'm not sure how TAC & SAC varied in terms of maintenance -- SAC generally was more anal about things being done exactly right, but I'm curious if mistakes were made.

I don't know where you got your information, but most of what you just stated is incorrect.

If a missile was dropped while loading or at any point during handling it was refused for use and sent to EOD for disposal. And dropping a missile isn't something that could go undetected. People tend to noticed when something that weighs a hundred pounds or more is dropped a few feet. It's not just the explosive hazard. There were more crushing injuries in munitions handling than any other injury.
Every missile fired from USAF aircraft ( I think) was a solid fuel missile, dropping it could crack the solid fuel. It was cast in a specific way to control the burn rate of the propellant. Additional cracks in the propellant would mean there would be much more propellant exposed for burning when the rocket motor was first ignited, in other words it could explode on ignition, or a uneven burn would make for a erratic flight path.
Some missiles and warheads were stored separate, and assembled just before use. The motors had weatherseals on the back, and that weather seal was to prevent the solid propellant from drying out, or absorbing moisture, either of which would effect it's burn rate, and a broken seal was a reason for refusal. Warheads were pretty well weather proofed themselves, plus were kept in completely weather proofed containers until assembly.
The weather in Vietnam wasn't much different from several places in the USA. You get away from the coast in several southern states, and it's about the same.
Even in the WW2 era, fuses and such were shipped and stored in very weather tight containers

As for the missile handling trucks not having shock absorbers, not true. They had springs and shocks just like any other vehicle . Plus the missile were usually hauled on trailers, and the trailers had springs,most had shocks too.
Shock absorbers are actually misnamed, they don't absorb the shock of a bump, the springs do that, the shocks just snub the reaction of the springs. Without shock absorbers springs with oscillate for several times after their compressed.

I was stationed at 7 different air bases when I was in the USAF, I don't remember any washboard surfaces meant to shake off FOD. Sometimes the roads from the munitions storage areas to the flight line may not have been the best roads on the base, but I doubt any effort was taken to make them rough.

 

[fliger747]

1000 rotations per second would require a twist rate in the 5"38 of one turn in about every 3' or less. I don't have the exact data for the 5' 38 but typically Naval Artillery might have a twist rate of about 1:20-25 calibers which works out to a full rotation once every 9-10' So about 1 1/2 rotations in a 16ft barrel. I come up with a WAG rotational figure of about 15,600 RPM. The "tubes" were located near the center of rotation such as to reduce the adverse effects the rotational effects. That the design actually worked is a testament to some rather good engineering!

As to whether or not the VT shells would be effective against high altitude aircraft is another question. An exploding shell at the right altitude (And a bomber formation was a somewhat stationary target altitude range wise) might be more effective than one that misses enough to not trigger the VT. Certainly the fuses were effective at closer range aircraft that might be closing range quickly, as in a direct low altitude approach.

I found a reference in 1 turn per 30 calibers... Gives me 12,400 RPM

 

[Shortround6]

One twist in 30 for the 5in/38 and perhaps it is calibers and not inches.

Getting time fuses to explode at the right height was quite a trick. There are two sources of error, one is getting the correct height of the bomber/formation and a 1% error at 20,000ft is 200ft.
2nd is the time fuse itself. Most had a tolerance of a certain percentage of the time they were set for. The time of flight to the 20,000ft area was such that many shells were exploding several hundred feet short. Germans tried an experiment of using contact fuses since the fuses seemed to have bigger error in the time of flight (point on the line where they exploded) than in getting the line of flight to intercept the target. I believe the experiment worked but it may have been in 1945 at which point it was too late.

VT fuses also eliminated another error, most guns had the fuses "set " before the round was put in the loading tray or breech and there was a several second delay between the fuse being set and the gun fired.
Some guns showed an increase in the rate of fire when VT fuses were used as the fuse setting step could be eliminated.

 

[bbear]

I was curious about the tube technology used in VT fuses. Apparently they did various ruses in design by orienting the parts structurally and filling the tubes with wax! A lot of genius in design, persistence and technical capability expended here! It was done by never say impossible types!

From memory, I can look up a passage in the book if you like, the earlier for example 45 fuzes used a perspex/plexiglass body (insulator), a tung bean oil "potting" and a can, an actual cylinder of tin, in side which the tubes were located.
The insulator allowed the antenna to operate as such.
The potting indeed dampened out shocks
The can kept the axes of the tubes in line and mechanically supported the joints of the wiring and tubes

later fuses used a
Teflon body insulator
A cerise wax 'potting'
No can

The tung bean oil (solid at room temperature) was the packing material used for the transport of valves (tubes) to from manufacturers to protect the valves (tubes) against rough handling.

Cerise wax, also solid at most ground temperatures, was better or cheaper than Tung bean oil.

The absence of a can is explained thus :
Centrifugal force can be used to separate heavy parts of a suspension from less dense parts. For example if a uniform diameter tube of human blood is laid radially to a centre of rotation and centrifuged at 10g for a minute or two the plasma accumulates towards the centre of rotation, the red blood cells towards the circumference of such a plate full of tubes (imagine the rounds of ammunition in a drum, as might be seen in a Lewis gun, points to the centre, rims to the rim as it were).

The same applies to the suspension of valves (tubes), wires, joints, suspended in the liquid wax. Believe it or not the tubes are the least dense parts of that suspension. So they all align very closely to the axis of rotation, the wax gets "spun" to the rim of the cavity. The faster the spin the greater the alignment. The fuzes were manufactured with the tubes very closely aligned, one atop the other along the axis of rotation, dependent on human dexterity. The valves (tubes) came into exact alignment because of the rotational violence done them in firing and the consequent centrifuge like effect.

This was important as one limitation of the technology was the noise at rotational frequency caused by mechanical stresses of off axis parts giving rise to electrostatic effects. That is charge distributed on one connector wire for example moving (vibrating) relative to another connection in a high impedance part of the circuit would cause a small movement of charge to and fro in that high impedance (sensing) part.

 

[fliger747]

Interesting information about these rather remarkable devices!

 

[basil]

@ bbear reply #103

Thx for the links but these are the sources which are mentioned in the Internet again and again without contributing to technical details or naming original sources.

Although GregP may be the only one here with practical fuze design knowlegde he first was not aware and / or did not believe that you could do a proximity fuze with vacuum technology although it was built hundred of thousand times and information about it is just a click away. And let´s not forget the Oslo Report of 1939 which contained parts of a German proximity fuze for atrillery shells.

I highly recommend reading Ralph B. Baldwin´s book "The Deadly Fuze" for a detailed story of the development of the proximity fuze in the US. Baldwin was part of the r&d team.

Btw it is quite certain that Rheinmetall developed an anti aircraft artillery proximity fuze based on passive electrostatic principles which was production ready at the end of WW2. It is mentioned by Fritz Trenkle (1982) in "Die deutschen Funklenkverfahren bis 1945" page 187 and in Adalbert Koch`s book (1954) "Die Geschichte der deutschen Flakartillerie 1933 - 1945" page 154. Both are very well researched books and rely on original sources.