The German proximity fuse.

Geoffrey Sinclair wrote:
The German proximity fuse.

The development of the US proximity fuse by the US in WW Two is
regarded as a unique allied triumph.

Little known however is that the Germans independently developed and
successfully test fired almost 1000 rounds of a similar proximity
fuse
near the wars end that if introduced into service would have had a
dramatic effect. The allies estimated that the availability of the
proximity fuse would force them to abandon use of the B-24 Liberator
due to its lower flying altitude compared to the B-17.

The B-24 made up around 1/3 of the 8th Air Force and 2/3 of the
15th Air force, all up just under half the USAAF bombers. The main
deployment of B-24s to Europe was in 1944.

It was a USAAF estimate, flak losses would triple, bombing heights
would have to increase and the B-24 not used against well defended
targets. When the German flak concentration around the main
synthetic
oil plants became so great the USAAF started to use cloudy days,
relying on radar aids, assuming the loss of accuracy for the gunners
was greater than that of the bombers.

Not flak losses were never above the critical loss rates, but would
have approached it if they were tripled. It took fighters to really
cut
up a bomber formation.


What were the critical levels? 10% losses would mean a 65% loss after
only 10 missions. 3% sounds sustainable.


The Allied Proximity fuse was used on both Anti-Aircraft Artillery
and
anti-personnel howitzers where they were set to explode
approximately
50 feet above the ground. At that height they would produce a lethal
zone over a terrifyingly wide area. When used against aircraft it
seemed to increase effectiveness of a round by 3-7 or more.

So the 16,000 88mm shells per shoot down fired would be reduced to
2,300 to 5,300. The Germans did better early in the war in terms of
shells per aircraft but this was the sort of price paid for using
effectively
reserve manpower in the flak units alongside less accurate fire
control
systems.

I suspect that the use of the proximity fuse would place pressure on
increasing accuracy. I suspect that barrels were not renewed as often
as was optimal.

The 128mm FLAK gun had a fuse setter installed on the barrel to allow
the fuse time to be set while the round was in the barrel.

It is my understanding that most 88 guns had an external fuse setting
device that was a box next to the barrel. So the FLAK crew (9 men or
children) would neet to maintain a rhythm of following the dials and
pointing the gun, inseting the round in the fuse setter removing it
inserting the round in the barrel etc.

Putting servo drives on the gun and in barrel fuse setters would I
suspect also have increased accuracy.

The problem is that there isn't enough skilled labour to build,
calibrate,maintain this equipement.




The proximity fuse effects can be replicated by wires on the bomb
noses and by having trees in the combat area. If the shell or bomb
hits the tree the results are an airburst. You can also have time
fuses for shells. Of course none as accurate as a proximity fuse
for bursts at the optimum height.

The proximity fuse was fielded as an AA weapon from ships in the
Pacific from June 1943 where it was reasoned that secrecy could not
be
compromised as dud rounds would fall into the sea. (I have no
knowledge of its use against the Japanese Troops on islands). It on
one occasion apparently helped shoot down 90 of 120 attacking
Japanese
planes.

As has been stated the last time this information was posted,

The claim ignores the USS Helena firing proximity fused shells off
Guadalcanal in January 1943. Fuse production was 500 per day
in October 1942. Note by the end of 1944 the delivery rate was
40,000 per day, or in other words just over half an hour to equal the
entire claimed German production.

The other point was to design a shell to take the fuse, the allies
started with the USN 5 inch gun.

It should be noted the claimed major shoot down was the USN
ships reporting what they thought they had shot down.

In the fights with Kamikazes the USN ships reported they needed
to fire 100% VT (proximity) fuses, since there was normally no time
to set and use time fuses.

It was first supplied to Britain to help overcome the V1 cruise
missile
fired at London where it in combination with radar and computer
directed guns reduced the mean number of rounds expended to destroy
a
V1 from 4000 to 180.

The note being it was a combination of better fire control and fuses.

It would appear that the 20:1 reduction came 3:1 from VT fuses and 7:1
from servo driven and computer aimed radar slaved guns. Or perhaps the
other way around.

I suspect optically directed servo driven computer aimed guns could
have been as effective on a clear day.



Finally there are records of it used against German troops during
the
Ardennes Offensive (Battle of Bulge). It was reasoned that the
Germans would not be able to reconstruct the fuses in time to make
use
of them. In fact the 'folklore' on the Internet is that they
captured some 20,000 but did not recognize them and also that they
recovered duds and reasoned that they were triggered by the Earth's
magnetic Field. (Note the magnet field theory probably came from
the
troops themselves before being analysed by more technical branches
of
the German forces)

Ah so the folk lore is they captured a US ammunition dump with
the fused shells and then inventoried the catch, as opposed to
destroying it?

I don't know what the custom would have been. It is said they didn't
recongise the nature of the shells. However they did recover dud
shells (they must have known there was something unique about them) and
surmised that they had a electronic fuse.



By the way the troops would not be checking the fusing of any
dud rounds, but removing the shells to a safer place. The
experts would be looking at things like fuses.

The allied fuse workings.

Technically the Allied fuse was not radar: it did not send out a
pulse
and listen for an echo. It had 4 tubes. One tube was part of the
oscillator. When a 'target' that was about a =BD wavelength in size
came within a few wavelengths it would load the amplifier and the
anode
current would increase. Two additional amplifiers would detect this
change and then triggered the 4th valve (a gas filled thyraton) to
set
of the detonator. Contrary to other reports it apparently did not
trigger on Doppler shift either or on frequency change. There were
many shock hardening techniques including planar electrodes and
packing
the components in wax and oil to equalize the stresses.

Given we are talking about wavelengths in the order of centimetres
the axis mist have been flying very small aircraft if they were
around
a half wavelength in size.

VT fuse opperated at about 220-280Mhz or so. A wavelenght would have
been about 1.5 meters. Targets would need to be 1/4 to 1/2 a
wavelenght to produce a stronger return.



Try this for an explanation,

"One method that was experimented with used radio waves transmitted
from the ground. These radio waves would be reflected by the target
and
received by the fuze. Once the radio waves were at a sufficient
level, the
fuze would activate causing the shell to explode.

Another method that was more logical and became the accepted means,
was to develop a fuze which was capable of obtaining its own
intelligence
and of using it to ignite the shell. When assembled this fuze
consisted of
four major parts: A miniature radio transceiver, complete with
amplifier
and capacitor; a battery; an explosive train; and the necessary
safety
devices. The theory was that the fuze transmitter, alone, would not
produce sufficient signal intensity, to trigger a thyratron tube
switch.
However, as the projectile approached a target the radio waves
reflected
by the target would gradually increase and come more and more into
phase
with the fuze-generated signal. Once the signal level was high
enough, the
fuze would know that the shell could do a maximum amount of damage,
and the thyratron tube switch would be triggered releasing the energy
in a
charged capacitor and thus igniting the shell."

The German fuse workings.

The fuse was based on electrostatic principles.

At least this hopefully stops the previous claims the Germans
handed the design to the British who then used it.

I never suggested that the Allies or British coppied the German fuse,I
suggested that it accelerated the allied work. Early German
investigations seem to go back to 1935. There is British work going to
1937 and I suspect 1934 for optical fuses.



The circuitry of the German fuse is not precisely known to me as I
do
not have the schematics however the details are in allied files
refred
to I do not have a circuit layout drawing. It is known that the
nose
of the shell was electrically insulated and isolated from the rest
of
the shell. It was built by the company Rheinmetall. The program was
halted in 1940 then restarted in early 1944 and then terminated
again
due to being over run by the allies at the point that it was ready
for
production.

The above assumes the program was producing fused shells in 1940
as opposed to heading towards the idea. After all if the restart was
in early 1944 and the production facilities were over run something
like
15 months later just as production was about to start it shows how
long
things actually took. How long the Germans really were from
production.

In actualy fact the 1000 test firings were conducted in 1944. There
may have been firings in 1940 before cancellation but they were almost
certainly not succesfull.


The US started work on the fuse in July 1940 and later developed
optical and magnetic proximity fuses for mines and 4.5 inch rockets.

Initial fuse testing demonstrated a sensitivity of 1-2 meters and a
reliability of 80% when fired against a metal cable target. A
circuit
adjustment yielded an increase to 3-4 meters and a reliability of
close
to 95%.

Further work showed a 10-15 meter sensitivity. This was with 88mm
canon shells. The shell to all intents and purposes ready for
production.

Again no dates are given, presumably we are to believe it was ready
for production in 1940, but then shut down because it was not ready
for production within 6 months, see below, and the time it actually
took in 1944/45 above.


No, I believe there were NO test firings in 1940 that were succesfull.

There were considerable strides made
during the war when it came to reliability and miniaturisation of
radio
parts, the later war experiments would have benefited from this.

There are some notes kicking around somewhere on german techniques for
valve seals in ceramic amplifier tubes. I believe they produced quite
small ceramic valves,



Note the lethal burst radius for a standard 88mm shell was around
30 feet, or 9 metres. Given the standard fire control radar some
59,000 88 mm shells were needed to cover the volume the aircraft
could be in when flying at 24,000 feet.

References are "Truth About the Wunderwaffen" by Igor Witowski who
cites "Proximity Fuse Development - Rheinmettal Borsig A.G.
Mullhausen. CIOS report ITEM nos 3 file nos XXVI -1 (1945)

Capacitance based fuses became highly developed after the second
world
war due to their high resistance against jamming techniques.

Ah, so the plan is to stop claiming the Germans gave the fuse to the
allies but to claim they thought of it first and did it better.

Electrostatic fuses are apparently intrinisically hightly resistent to
jamming.

The allies looked at using electrostatic principles but preceded with
radio methods instead. I belive the Germans struggled to get the range
up from 3-4 meters to 10-14 meters. It looks like they had to add a
small antenna cable or tailing wire to achieve this.



It is unlikely that the shell could have been easily degraded by
jamming or chaff. (unlike the Allied shell).

Yes, claim it does things better. Just ignore the idea the whole
idea
of window was to mimic a bomber, and all that has to be done now
is to explain how the shell would discriminate against aluminium
in falling foils and in aircraft flying along.

Window and Chaff could be used to form a layer below the bomber to
predetonate some of the fuses.





I can speculate as to several ways that this might work. It is
referred to as a "influenz zunder" based in electrostatic
principles.

Method 1: Bridge Cicuit. The shells external capacitance is made
part of a bridge circuite with an internal reference capacitor in
the
other arm. Any disturbance caused by an large object such as an
aircraft would cause a current to flow across the bridge that would
be
amplified.

main problem, surviving the firing accelerations.

True, but they seem to have succeded.


Method 2: QT or charge transfer methods. A high speed vibrating
contact charges the shell and then discharges it into a known
capacitance which is then measured.

Should be fun to create the mechanism to allow a high speed
vibrating contact, have it survive the acceleration of the firing
and then spin up to arm the shell

The contact could be aligned along the axis to avoid centrifugal forces
or a rotating button could be used.



Method 3: making the shell body part of a resonant circuit and
detecting frequency changes.

Should be fun lugging the fused shells around metal guns.

I can not find the precise reason for the abandonment of the work in
1940 however it probably relates to the 'fuhrer befehle' or fuhrer
directive that with few exceptions all work that could not be put
into
production within 6 months were to be terminated to increase
resources
for those that could (in order to support operation Barborosa).

So in other words in 1940 the fuse was not ready for production.

No it wasn't.

Production of 1000 rounds occured for testing in 1944.



It
was at this time that the Germans also abandoned their magnetron and
microwave development teams and programs. Many programs suffered
severely due to this; something that was to have far reaching
consequences for the German war effort.

It would be better to say scaled back as opposed to abandoned.

Abandoned is accurate. They had to get the personel back out of the
Army. They didn't even recognise the value of the magnetron since the
microwave experts werent there to look at it. It was taken by some
initally as proof that microwaves are not good for detecting aircraft.



What would have happened if the proximity fuse was not abandoned in
1940 but development continued such that it entered service in 1943?

The USAAF would have flown more night missions and deployed
B-29s to Europe.

The B29 wasn't reliable till late 44. The engines overheated, caught
fire (they were magnesium) and then burned through the spar. Nasty.

The allies would have devoted more to flak
suppression. The allies would have flown more missions on
cloudy days using the better navigation aids in 1944.

Note the half way point for Bomber Command for bombs on Germany
was in late September 1944, the 8th was mid November 1944. It
was a very end loaded campaign.

The number of flak batteries out ran the German ability to provide
them with proper fire control systems. Hence there were still sound
locators in use in 1944 to use an extreme example. The idea of
massed batteries was also driven by the amount of fire control
systems needed.

All guns fired at once apparently.



Before the RAF introduced window Bomber Command was recording
that around 6 to 9% of returning aircraft on night missions had flak
damage, March to July 1943. This dropped to 2.85% in August and
averaged 2.3% for all of 1944 and 1.4% for 1945. Window remained
effective against the fire control radars for the remainder of the
war.

An moving target indicator called k-laus that used a 2 microsecond
delay line to detect moving targets was expected to resolve window and
chaff much better than wurzlaus and nurenberg. It didn't quite enter
service.



The average for aircraft returning damaged by flak on night raids
February to December 1942 was 6.5%, for all of 1943 5.8%. In effect
a proximity fuse at around 3 to 7 times the lethality would restore
to
exceed the pre window hit rates.

The USAAF carried window and active jammers but, of course, by day
the gunners could correct their aim by eye. Some batteries even had
the ability to track the H2X radars of USAAF pathfinders and use this
for ranging, electronic warfare was a 2 way street.
=20
Geoffrey Sinclair
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