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{{short description|Automatic fuze that detonates an explosive
{{Use dmy dates|date=October 2020}}
[[Image:MK53 fuze.jpg|upright=1.35|thumb|Proximity fuze MK53 removed from shell, circa 1950s]]
A '''proximity fuze''' (
==Background==
Before the invention of the proximity fuze, detonation was induced by direct contact, a timer set at launch, or an altimeter. All of these earlier methods have disadvantages. The probability of a direct hit on a small moving target is low; a shell that just misses the target will not explode. A time- or height-triggered fuze requires good prediction by the gunner and accurate timing by the fuze. If either is wrong, then even accurately aimed shells may explode harmlessly before reaching the target or after passing it. At the start of [[
Proximity fuzes are also useful for producing [[air burst]]s against ground targets. A contact fuze would explode when it hit the ground; it would not be very effective at scattering shrapnel. A timer fuze can be set to explode a few meters above the ground but the timing is vital and usually requires [[Artillery observer|observers]] to provide information for adjusting the timing. Observers may not be practical in many situations, the ground may be uneven, and the practice is slow in any event. Proximity fuzes fitted to such weapons as [[artillery shell|artillery]] and [[mortar shell]]s solve this problem by having a range of set burst heights [e.g. {{cvt|2|,|4|or|10|m|ft|0}}] above ground that are selected by gun crews. The shell bursts at the appropriate height above ground.
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The fuze was later found to be able to detonate artillery shells in [[air burst]]s, greatly increasing their anti-personnel effects.{{sfn|Baldwin|1980|pp=xxxi, 279}}
In Germany, more than 30 (perhaps as many as 50){{sfn|Holmes|2020|p=272}} different proximity fuze designs were developed, or researched, for anti-aircraft use, but none saw service.{{sfn|Baxter|1968|p=222}} These included acoustic fuzes triggered by engine sound, one
In the post-World War II era, a number of new proximity fuze systems were developed,
===Design in the UK===
The first reference to the concept of radar in the UK was made by [[W. A. S. Butement]] and P. E. Pollard, who constructed a small [[breadboard]] model of a pulsed radar in 1931. They suggested the system would be useful for
In 1936, the [[Air Ministry]] took over [[Bawdsey Manor]] in [[Suffolk]] to further develop their prototype radar systems that
As these projects moved from development into prototype form in the late 1930s, Butement turned his attention to other concepts, and among these was the idea of a proximity
{{quote|...Into this stepped W. A. S. Butement, designer of radar sets [[Chain Home Low|CD/CHL]] and [[GL Mk. I radar|GL]], with a proposal on 30 October 1939 for two kinds of radio fuze: (1) a radar set would track the projectile, and the operator would transmit a signal to a radio receiver in the fuze when the range, the difficult quantity for the gunners to determine, was the same as that of the target and (2) a fuze would emit high-frequency radio waves that would interact with the target and produce, as a consequence of the high relative speed of target and projectile, a Doppler-frequency signal sensed in the oscillator.<ref>{{citation |last=Brown |first=Louis |title=A Radar History of World War II |publisher=Inst. of Physics Publishing |year=1999 |at=section 4.4.}}</ref>}}
In May 1940, a formal proposal from Butement, Edward Shire, and Amherst Thomson was sent to the British Air Defence Establishment based on the second of the two concepts.<ref name="Brennan, 1968" /> A
Prototype fuzes were then constructed in June 1940, and installed in "unrotated projectiles", the British cover name for solid-fueled [[rocket]]s, and fired at targets supported by balloons.<ref name="Brennan, 1968" /> Rockets have relatively low acceleration and no spin creating [[centrifugal force]], so the stresses on the delicate electronic fuze are relatively benign. It was understood that the limited application was not ideal; a proximity fuze would be useful on all types of artillery and especially anti-aircraft artillery, but those had very high accelerations.
As early as September 1939, [[John Cockcroft]] began a development effort at [[Pye Ltd.]] to develop [[thermionic valve]]s (electron tubes) capable of withstanding these much greater forces.<ref>[http://www.pyetelecomhistory.org/prodhist/military/military.html Anti-Aircraft Radio Proximity Fuze (1939–1942) (conceptual and prototype design work)]</ref> Pye's research was transferred to the United States as part of the technology package delivered by the Tizard Mission when the United States entered the war. Pye's group was apparently unable to get their rugged [[pentode]]s to function reliably under high pressures until 6 August 1941, which was after the successful tests by the American group.<ref>{{Cite book |last=Frankland |first=Mark |date=2002 |url=https://books.google.com/books?id=ArZ3dc_eq2wC&q=Mark+Franklan,+radio+man|title=Radio Man: The Remarkable Rise and Fall of C.O. Stanley|publisher=IET |isbn=978-0-85296-203-9}}</ref>{{sfn|Holmes|2020|p=304}}
Looking for a short-term solution to the valve problem, in 1940 the British ordered 20,000 miniature electron tubes intended for use in [[hearing aid]]s from [[Western Electric Company]] and [[Radio Corporation of America]]
In September 1940, the Tizard Mission travelled to the US to introduce their researchers to a number of UK developments, and the topic of proximity fuses was raised. The details of the British experiments were passed to the [[United States Naval Research Laboratory]] and [[National Defense Research Committee]] (NDRC).<ref name="Brennan, 1968" /> Information was also shared with [[Canada]] in 1940 and the [[National Research Council (Canada)|National Research Council]] of Canada delegated work on the fuze to a team at the [[University of Toronto]].<ref>{{cite book |last=Friedland |first=Martin L. |date=2002 |title=The University of Toronto: A History |edition=1st |url=https://archive.org/details/universityoftoro0000frie |url-access=registration |location=Toronto |publisher=University of Toronto Press |pages=[https://archive.org/details/universityoftoro0000frie/page/354 354]–355 |isbn=978-0802044297 }}</ref>
===
Prior to and following receipt of circuitry designs from the British, various experiments were carried out by Richard B. Roberts, Henry H. Porter, and Robert B. Brode under the direction of NDRC Section T Chairman Merle Tuve.<ref name="Brennan, 1968" /> Tuve's group was known as Section T, which was located at APL throughout the war.<ref>{{Cite book |last=Baxter |first=James Phinney |url=https://books.google.com/books?id=57lgAAAAIAAJ |title=Scientists Against Time |date=1946 |publisher=Little, Brown |isbn=978-0598553881}}</ref> As Tuve later put it in an interview: "We heard some rumors of circuits they were using in the rockets over in England, then they gave us the circuits, but I had already articulated the thing into the rockets, the bombs and shell."{{sfn|Holmes|2020|p=304}}<ref>{{Cite web|date=2015-04-17 |title=Merle Tuve |url=https://www.aip.org/history-programs/niels-bohr-library/oral-histories/3894 |access-date=2020-06-10 |website=www.aip.org |language=en}}</ref> As Tuve understood, the circuitry of the fuze was rudimentary. In his words, "The one outstanding characteristic in this situation is the fact that success of this type of fuze is not dependent on a basic technical idea{{snd}}all of the ideas are simple and well known everywhere."{{sfn|Holmes|2020|p=304}} The critical work of adapting the fuze for anti-aircraft shells was done in the United States, not in England.{{sfn|Holmes|2020|pp=304–305}} Tuve
A key improvement was introduced by [[Lloyd Berkner]], who developed a system using separate transmitter and receiver circuits. In December 1940, Tuve invited [[Harry Diamond (engineer)|Harry Diamond]] and Wilbur S. Hinman, Jr, of the United States [[National Bureau of Standards]] (NBS) to investigate Berkner's improved fuze and develop a proximity fuze for rockets and bombs to use against
In just two days, Diamond was able to come up with a new fuze design and managed to demonstrate its feasibility through extensive testing at the [[Naval Surface Warfare Center Dahlgren Division|Naval Proving Ground]] at Dahlgren, Virginia.<ref name="Hinman-1957">{{Cite journal |title=Portrait of Harry Diamond| last=Hinman | first=Wilbur Jr. |journal=Proceedings of the IRE |volume=45 |issue=4 |pages=443–444 |doi=10.1109/JRPROC.1957.278430 |year=1957}}</ref><ref>{{Cite web |title=Artillery Proximity Fuses |website=warfarehistorynetwork.com |url=http://warfarehistorynetwork.com/daily/wwii/artillery-proximity-fuses/ |access-date=2018-06-18 |archive-date=12 June 2018 |archive-url=https://web.archive.org/web/20180612212300/http://warfarehistorynetwork.com/daily/wwii/artillery-proximity-fuses/ |url-status=dead }}</ref> On 6 May 1941, the NBS team built six fuzes which were placed in air-dropped bombs and successfully tested over water.<ref name="Brennan, 1968"/>
Given their previous work on radio and radiosondes at NBS, Diamond and Hinman developed the proximity fuze which employed the [[Doppler effect]] of reflected radio waves.<ref name="Cochrane-1976" /><ref name="NIST-2018">{{Cite web |url=https://nvlpubs.nist.gov/nistpubs/sp958-lide/059-062.pdf |title=Radio Proximity Fuzes|access-date=18 June 2018}}</ref><ref name="Johnson-1984">{{Cite journal |last1=Johnson |first1=John |last2=Buchanan |first2=David |last3=Brenner |first3=William |date=July 1984 |title=Historic Properties Report: Harry Diamond Laboratories, Maryland and Satellite Installations Woodbridge Research Facility, Virginia and Blossom Point Field Test Facility, Maryland |url=http://www.dtic.mil/docs/citations/ADA175872 |archive-url=https://web.archive.org/web/20170609010919/http://www.dtic.mil/docs/citations/ADA175872 |url-status=dead |archive-date=9 June 2017 |journal=Defense Technical Information Center |language=en}}</ref> The use of the Doppler effect developed by this group was later incorporated in all radio proximity fuzes for bomb, rocket, and mortar applications.<ref name="USArmy-1963" /> Later, the Ordnance Development Division of the National Bureau of Standards (which became the [[Harry Diamond Laboratories]] – and later merged into the [[United States Army Research Laboratory|Army Research Laboratory]] – in honor of its former chief in subsequent years) developed the first automated production techniques for manufacturing radio proximity fuzes at
While working for a defense contractor in the mid-1940s, Soviet spy [[Julius Rosenberg]] stole a working model of an American proximity fuze and delivered it to Soviet intelligence.<ref>{{citation |first1=John Earl |last1=Haynes |first2=Harvey |last2=Klehr |title=Venona, Decoding Soviet Espionage in America |page=303}}</ref> It was not a fuze for anti-aircraft shells, the most valuable type.{{sfn|Holmes|2020|p=274}}
In the US, NDRC focused on radio fuzes for use with anti-aircraft artillery, where acceleration was up to 20,000 {{mvar|g}},
A particularly successful application was the 90 mm shell with VT fuze with the [[SCR-584]] automatic tracking radar and the
====VT (Variable Time)====
The Allied fuze used constructive and destructive [[wave interference|interference]] to detect its target.{{sfn|Bureau of Ordnance|1946|pp=32–37}} The design had four or five electron tubes.<ref>{{harvnb|Bureau of Ordnance|1946|p=36}} shows a fifth tube, a [[diode]], used for a low trajectory wave suppression feature (WSF).</ref> One tube was an oscillator connected to an antenna; it functioned as both a transmitter and an [[autodyne]] detector (receiver). When the target was far away, little of the oscillator's transmitted energy would be reflected to the fuze. When a target was nearby, it would reflect a significant portion of the oscillator's signal. The amplitude of the reflected signal corresponded to the closeness of the target.<ref group=notes>The return signal is inversely proportional to the fourth power of the distance.</ref> This reflected signal would affect the oscillator's plate current, thereby enabling detection.
However, the [[Phase (waves)|phase relationship]] between the oscillator's transmitted signal and the signal reflected from the target varied depended on the round trip distance between the fuze and the target. When the reflected signal was in phase, the oscillator amplitude would increase and the oscillator's plate current would also increase. But when the reflected signal was out of phase then the combined radio signal amplitude would decrease, which would decrease the plate current. So the changing phase relationship between the oscillator signal and the reflected signal complicated the measurement of the amplitude of that small reflected signal.
This problem was resolved by taking advantage of the change in frequency of the reflected signal. The distance between the fuze and the target was not constant but rather constantly changing due to the high speed of the fuze and any motion of the target. When the distance between the fuze and the target changed rapidly, then the phase relationship also changed rapidly. The signals were in-phase one instant and out-of-phase a few hundred microseconds later. The result was a [[heterodyne]] beat frequency which corresponded to the velocity difference. Viewed another way, the received signal frequency was [[Doppler shift|Doppler-
In order to be used with gun projectiles, which experience extremely high acceleration and centrifugal forces, the fuze design also needed to utilize many shock
The designation VT means 'variable time'.<ref name="DTIC-1946a">{{Cite report|title=Summary Technical Report of the National Defence Research Council|date=1946|chapter-url=
===Development===
The anti-aircraft artillery range at [[Kirtland Air Force Base]] in New Mexico was used as one of the test facilities for the proximity fuze, where almost 50,000 test firings were conducted from 1942 to 1945.<ref>{{Cite magazine|title=Request for information about the Isleta Pueblo Ordnance Impact Area |date=8 August 2008 |author=U.S. Army Corps of Engineers |magazine=Isleta Pueblo News |volume=3 |issue=9 |page=12 |url=http://www.isletapueblo.com/uploads/3/0/9/5/3095182/08_august_2008.pdf |archive-url=https://web.archive.org/web/20170326184510/http://www.isletapueblo.com/uploads/3/0/9/5/3095182/08_august_2008.pdf |archive-date=26 March 2017 |url-status=live}}</ref> Testing also occurred at [[Aberdeen Proving Ground]] in Maryland, where about 15,000 bombs were
[[US Navy]] development and early production was outsourced to the [[Wurlitzer]] company, at [[North Tonawanda Barrel Organ Factory|their barrel organ factory]] in [[North Tonawanda, New York]].<ref>{{cite book|url=https://books.google.com/books?id=FhoEAAAAMBAJ&pg=PT122 |title=Navy presents high award to Wurlitzer men|publisher=Billboard magazine|date=15 June 1946}}</ref>
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First large scale production of tubes for the new fuzes<ref name="Brennan, 1968" /> was at a [[General Electric]] plant in [[Cleveland, Ohio]] formerly used for manufacture of Christmas-tree lamps. Fuze assembly was completed at General Electric plants in [[Schenectady, New York]] and [[Bridgeport, Connecticut]].<ref name="Miller, Men and Volts" >{{Citation |last=Miller |first=John Anderson |title=Men and Volts at War |journal=Nature |volume=161 |issue=4082 |pages=113 |publisher=McGraw-Hill Book Company |location=New York |year=1947|bibcode=1948Natur.161..113F |doi=10.1038/161113a0 |s2cid=35653693 |doi-access=free }}</ref> Once inspections of the finished product were complete, a sample of the fuzes produced from each lot was shipped to the National Bureau of Standards, where they were subjected to a series of rigorous tests at the specially built Control Testing Laboratory.<ref name="NIST-2018" /> These tests included low- and high-temperature tests, humidity tests, and sudden jolt tests.
By 1944, a large proportion of the American [[electronics industry]] concentrated on making the fuzes. Procurement contracts increased from [[US$]]60 million in 1942, to $200 million in 1943, to $300 million in 1944 and were topped by $450 million in 1945. As volume increased, efficiency came into play and the cost per fuze fell from $732 in 1942 to $18 in 1945. This permitted the purchase of over 22 million fuzes for approximately one billion dollars ($14.6 billion in 2021 USD<ref>{{Cite web|title=Calculate the Value of $1.00 in 1945. How much is it worth today?|url=https://www.dollartimes.com/inflation/inflation.php?amount=1&year=1945?back=https://www.google.com/search?client=safari&as_qdr=all&as_occt=any&safe=active&as_q=One+dollar+in+1945+inflation+adjusted&channel=aplab&source=a-app1&hl=en |access-date=2021-09-01 |website=www.dollartimes.com}}</ref>). The main suppliers were [[Powel Crosley, Jr.#Crosley's war effort|Crosley]], [[RCA]], [[Eastman Kodak]], [[McQuay-Norris]] and [[Sylvania Electric Products|Sylvania]]. There were also over two thousand suppliers and subsuppliers, ranging from powder manufacturers to machine shops.{{sfn|Sharpe|2003}}{{sfn|Baldwin|1980|pp=217–220}} It was among the first mass-production applications of [[printed circuit]]s.<ref>{{cite book |last1=Eisler|first1=Paul|last2=Williams|first2=Mari |title=My Life with the Printed Circuit|publisher=Lehigh University Press |year=1989|isbn=978-0-934223-04-1}}</ref>
===Deployment===
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* It was used in Europe starting in the [[Battle of the Bulge]] where it was very effective in artillery shells fired against German infantry formations, and changed the tactics of land warfare.
At first the fuzes were only used in situations where they could not be captured by the Germans. They were used in land-based artillery in the South Pacific in 1944. Also in 1944, fuzes were allocated to the [[British Army]]'s [[Anti-Aircraft Command]], that was engaged in defending Britain against the V-1 flying bomb. As most of the British heavy anti-aircraft guns were deployed in a long, thin coastal strip (leaving inland free for fighter interceptors), dud shells fell into the sea, safely out of reach of capture. Over the course of the German V-1 campaign, the proportion of flying bombs that were destroyed flying through the coastal gun belt
The Pentagon refused to allow the Allied field artillery use of the fuzes in 1944, although the United States Navy fired proximity-fuzed anti-aircraft shells in the July 1943 [[Battle of Gela (1943)|Battle of Gela]] during the invasion of Sicily.<ref>{{cite book |last1=Potter |first1=E.B. |last2=Nimitz |first2=Chester W. |author-link2 =Chester W. Nimitz |title =Sea Power |url=https://archive.org/details/seapowernavalhis0000pott |url-access=registration |publisher =Prentice-Hall |date =1960 |location =Englewood Cliffs, New Jersey |pages =[https://archive.org/details/seapowernavalhis0000pott/page/589 589]–591 |isbn=978-0137968701 |via=Internet Archive}}</ref> After General [[Dwight D. Eisenhower]] demanded he be allowed to use the fuzes, 200,000 shells with VT fuzes (code named "POZIT"<ref>{{cite book|author=Albert D. Helfrick|title=Electronics in the Evolution of Flight |url=https://books.google.com/books?id=EumPJQBViz4C&pg=PA78|year=2004|publisher=Texas A&M UP|page=78|isbn=978-1585444137}}</ref>) were used in the Battle of the Bulge in December 1944. They made the Allied heavy artillery far more devastating, as all the shells now exploded just before hitting the ground.<ref>{{cite book|author=Rick Atkinson|title=The Guns at Last Light: The War in Western Europe, 1944-1945|url=https://books.google.com/books?id=FUQ9lEHO0QoC&pg=PA460|year=2013|pages=460–462, 763–764|publisher=Henry Holt and Company |isbn=978-1429943673}}</ref> German divisions were caught out in open as they had felt safe from timed fire because it was thought that the bad weather would prevent accurate observation. U.S. General [[George S. Patton]] credited the introduction of proximity fuzes with saving Liège and stated that their use required a revision of the tactics of land warfare.{{sfn|Bush|1970|p=112}}
Bombs and rockets fitted with radio proximity fuzes were in limited service with both the [[United States Army Air Forces|USAAF]] and USN at the end of WWII. The main targets for these proximity fuze detonated bombs and rockets were [[anti-aircraft]] emplacements and [[Aerodrome|airfields]].<ref name="DTIC-1946b">{{Cite report|title=Summary Technical Report of the National Defence Research Council|date=1946|chapter-url=
==Sensor types==
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|patent-number=3152547
|country-code=US
|url=
}}</ref> works as follows: The shell contains a micro-[[transmitter]] which uses the shell body as an [[antenna (radio)|antenna]] and emits a continuous wave of roughly 180–220 MHz. As the shell approaches a reflecting object, an interference pattern is created. This pattern changes with shrinking distance: every half wavelength in distance (a half wavelength at this frequency is about 0.7 meters), the transmitter is in or out of resonance. This causes a small cycling of the radiated power and consequently the oscillator supply current of about 200–800 Hz, the [[Doppler effect|Doppler]] frequency. This signal is sent through a [[band-pass filter]], amplified, and triggers the detonation when it exceeds a given amplitude.{{cn|date=April 2023}}
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Optical sensing was developed in 1935, and patented in the [[United Kingdom]] in 1936, by a Swedish inventor, probably Edward W. Brandt, using a [[petoscope]]. It was first tested as a part of a detonation device for bombs that were to be dropped over bomber aircraft, part of the UK's Air Ministry's "bombs on bombers" concept. It was considered (and later patented by Brandt) for use with anti-aircraft missiles fired from the ground. It used then a toroidal lens, that concentrated all light from a plane perpendicular to the missile's main axis onto a photocell. When the cell current changed a certain amount in a certain time interval, the detonation was triggered.
Some modern [[air-to-air missile]]s (e.g., the [[ASRAAM]] and [[AA-12 Adder]]) use [[laser]]s to trigger detonation. They project narrow beams of laser light perpendicular to the flight of the missile. As the missile cruises towards its target the laser energy simply beams out into space. As the missile passes its target some of the energy strikes the target and is reflected to the missile, where detectors sense it and detonate the warhead.
=== Acoustic ===
[[Acoustics|Acoustic]] proximity fuzes are actuated by the acoustic emissions from a target (example an aircraft's engine or ship's propeller). Actuation can be either through an electronic circuit coupled to a [[microphone]], or [[hydrophone]], or mechanically using a resonating vibratory reed connected to diaphragm tone filter. <ref name="Hogg-1999">{{Cite book|title=German Secret Weapons of the Second World War|last=Hogg|first=Ian|date=1999|publisher=Frontline Books|isbn=978-1-8483-2781-8|pages=120–122|language=en}}</ref> <ref name="NDRC-1946">{{Cite report|title=Summary Technical Report of the National Defence Research Council|date=1946|chapter-url=
During WW2, the Germans had at least five acoustic fuzes for [[Anti-aircraft warfare|anti-aircraft]] use under development, though none saw operational service. The most developmentally advanced of the German acoustic fuze designs was the [[Rheinmetall-Borsig]] Kranich (German for [[Crane (bird)|Crane]]) which was a mechanical device utilizing a diaphragm tone filter sensitive to frequencies between 140 and
During [[WW2]], the [[National Defense Research Committee]] (NDRC) investigated the use of acoustic proximity fuzes for [[Anti-aircraft warfare|anti-aircraft]] weapons but concluded that there were more promising technological approaches. The NDRC research highlighted the [[speed of sound]] as a major limitation in the design and use of acoustic fuzes, particularly in relation to missiles and high-speed aircraft.<ref name="NDRC-1946"/>
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=== Magnetic ===
[[File:Luftmine (LM).jpg|thumb|
{{main|Magnetic proximity fuze|Magnetic pistol}}
Magnetic sensing can only be applied to detect huge masses of iron such as ships. It is used in mines and torpedoes. Fuzes of this type can be defeated by [[degaussing]], using non-metal hulls for ships (especially [[Minesweeper (ship)|minesweepers]]) or by [[electromagnetic induction|magnetic induction]] loops fitted to aircraft or towed [[buoy]]s.
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Some naval mines use pressure fuzes which are able to detect the [[P-wave|pressure wave]] of a [[ship]] passing overhead. Pressure sensors are usually used in combination with other fuze detonation technologies such as [[Acoustics|acoustic]] and [[electromagnetic induction|magnetic induction]].<ref name="Erickson-2009"/>
During WW2, pressure activated fuzes were developed for sticks (or trains) of [[bombs]] to create above ground [[Air burst|airbursts]].
== Gallery ==
<gallery heights="200">
File:PD and Proximity fuze.jpg|A
File:M734 Section.jpg|Cross-section of a M734 radar proximity fuze
</gallery>
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|publisher= [[William Morrow and Company]], Inc.
}}
* {{Cite book|last=Holmes|first=Jamie|title=12 Seconds of Silence: How a Team of Inventors, Tinkerers, and Spies Took Down a Nazi Superweapon|date=2020|publisher=Houghton Mifflin Harcourt|isbn=978-1-328-46012-7 |url=https://books.google.com/books?id=fyKixgEACAAJ}}
* {{Citation
|last= Sharpe
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==Further reading==
* {{citation |last=Allard |first=Dean C. |title=The Development of the Radio Proximity Fuze |journal=Johns Hopkins APL Technical Digest |date=1982 |volume=3 |issue=4 |pages=358–359 |url=https://www.jhuapl.edu/Content/techdigest/pdf/V03-N04/03-04-Allard.pdf}}
* {{cite web |last1=Allen |first1=Kevin |title=Artillery Proximity Fuses |website=Warfare History Network |url=http://warfarehistorynetwork.com/daily/wwii/artillery-proximity-fuses/ |access-date=4 June 2018 |archive-date=12 June 2018 |archive-url=https://web.archive.org/web/20180612212300/http://warfarehistorynetwork.com/daily/wwii/artillery-proximity-fuses/ |url-status=dead }}
* {{Citation
|last= Bennett
|first= Geoffrey
|author-link= Geoffrey Bennett (historian)
|title= The Development of the Proximity Fuze
|journal= Journal of the Royal United Service Institution
| |||