However, while the Boxer time fuze was a great advance various problems had to be dealt with over the following years. They were replaced in army service in by those designed by Mr Pettman, these could be used with both spherical and non-spherical shells. The final Boxer time fuze, for mortars, appeared in and the army retained wooden fuzes although the navy used metal ones.
There was a similar American wooden fuze. The problem was that there was little or no windage between the shell and the barrel, so the propelling charge could no longer be used to ignite the fuze. Therefore, a primer was added with a hammer suspended above it, the shock of firing released the hammer which initiated the primer to ignite the powder time train.
The introduction of RBL guns led to non-spherical projectiles, which landed nose first. This enabled percussion nose fuzes, but they had to cope with the spinning shell and centrifugal forces. Its percussion function was not entirely successful and was soon replaced by the E Mk III fuze, made of brass it contained a ring of slow burning composition ignited by a pellet holding a detonator cap that was set back onto a firing pin by the shock of firing. Since the second half of the 19th century, most artillery fuzes are fitted to the nose of the projectile.
The depth of recess can vary with the type of shell and fuze. Artillery fuzes were sometimes specific to particular types of gun or howitzer due to their characteristics, notable differences in muzzle velocity and hence the sensitivity of safety and arming mechanisms. However, by World War 2, while there were exceptions, most fuzes of one nation could be used with any required artillery shell of that nation, if it could be physically fitted to it, although different army and navy procurement arrangements often prevented this.
The exceptions were mortar bomb fuzes, and this continues.
The extremes being the firing pin and detonator close to the nose with a long flash tube to the booster typical in US designs , or a long firing pin to a detonator close to the booster and a short flash tube typical in British designs. For other military fuzes, see Fuze. Magnetic sensing can only be applied to detect huge masses of iron such as ships. However, by the 18th century time fuzes were aimed to function in the air and in the s proximity fuzes were introduced to achieve more precisely positioned airburst. There was little standardisation, well into the 19th century, in British service, virtually every calibre had its own time fuze.
An early action in NATO standardisation was to agree the dimensions and threads of the fuze recess in artillery projectiles to enable fuze interchangeability between nations. Modern artillery fuzes can generally be used with any appropriate artillery shell, including naval ones. However, smoothbore mortars, constrain the choice of safety and arming mechanisms because there is no centrifugal force and muzzle velocities are relatively low.
Therefore, shell fuzes cannot be used with mortar bombs, and mortar fuzes are unsuitable for the higher velocities of shells. The fuze action is initiated by impact, elapsed time after firing or proximity to a target. These contents may be lethal, such as the now-obsolete shrapnel shell or modern sub-munitions, or non-lethal such as canisters containing a smoke compound or a parachute flare. Fuzes normally have two explosive components in their explosive train: This booster is powerful enough to detonate the main charge in a high-explosive shell or the ejecting charge in a carrier shell.
The two charges are typically connected by a 'flash tube'. The safety and arming arrangements in artillery fuzes are critical features to prevent the fuze functioning until required, no matter how harsh its transport and handling. Some older types of fuze also had safety features such as pins or caps removed by the user before loading the shell into the breach. Defective fuzes can function while the shell is in the barrel - a 'bore premature', or further along the trajectory. Different fuze designs have different safety and arming mechanisms that use the two forces in various ways.
Subsequently, centripetal devices were generally preferred for use with low-velocity howitzer shells because the set-back was often insufficient. However, late 19th- and 20th-century designs used more sophisticated combinations of methods that applied the two forces. Modern safety and arming devices are part of an overall fuze design that meets insensitive munitions requirements. This includes careful selection of the explosives used throughout the explosive train, strong physical barriers between the detonator and booster until the shell is fired and positioning explosive components for maximum protection in the fuze.
In the 20th century, most fuzes were 'percussion'. Percussion fuzes remain widespread particularly for training. War stocks in western armies are now predominantly 'multi-function' offering a choice of several ground and airburst functions.
Direct action fuzes function by the fuze nose hitting something reasonably solid, such as the ground, a building or a vehicle, and pushing a firing pin into a detonator. The early British fuze at left is an example. Direct action fuze designs are 'super-quick' but may have a delay option. The extremes being the firing pin and detonator close to the nose with a long flash tube to the booster typical in US designs , or a long firing pin to a detonator close to the booster and a short flash tube typical in British designs.
Graze fuzes function when the shell is suddenly slowed down, e. This deceleration causes the firing pin to move forward, or the detonator to move backward, sharply and strike each other. Graze is the only percussion mechanism that can be used in base fuzes.
This is an original Union Frankford Arsenal five second fuze pack containing five unused fuzes for artillery cannon shells. These fuzes would have been. (2) Packet of five 10 second paper time fuzes. (3) Arrick "Eureka" time fuze, brass. (4) Absterdam percussion fuze, brass. (5) Britten percussion fuze, brass.
Direct action fuzes can have a delay function, selected at the gun as an alternative to direct action. Delay may use a graze function or some other mechanism. Special 'concrete piercing' fuzes usually have only a delay function and a hardened and strengthened fuze nose. Base fuzes are enclosed within the base of the shell and are hence not damaged by the initial impact with the target. Their delay timing may be adjustable before firing. They use graze action and have not been widely used by field artillery. Base fuzed shells were used by coast artillery and warships against armoured warships into the s.
Airburst fuzes, using a preset timing device initiated by the gun firing, were the earliest type of fuze. They were particularly important in the 19th and early 20th Centuries when shrapnel fuzes were widely used. They again became important when cluster munitions became a major element in Cold War ammunition stocks, and the moves to multi-function fuzes in the late 20th century mean that in some western countries airburst fuzes are available with every shell used on operations.
Time fuzes were essential for larger calibre anti-aircraft guns, and it soon became clear that igniferous fuzes were insufficiently accurate and this drove the development of mechanical time fuzes between the world wars. During World War 2 radio proximity fuzes were introduced, initially for use against aircraft where they proved far superior to mechanical time, and at the end of for field artillery.
Artillery Time fuzes detonate after a set period of time. Early time fuzes were igniferous i.
Clockwork mechanisms appeared at the beginning of the 20th century and electronic time fuzes appeared in the s, soon after digital watches. Almost all artillery time fuzes are fitted to the nose of the shell. One exception was the s design US 8-inch nuclear shell M that had a triple-deck mechanical time base fuze. The time length of a time fuze is usually calculated as part of the technical fire control calculations, and not done at the gun although armies have differed in their arrangements. The fuze length primarily reflects the range to the target and the required height of burst.
High height of burst, typically a few hundred metres, is usually used with star shell illuminating shell and other base ejecting shells such as smoke and cluster munitions, and for observing with high-explosive HE shells in some circumstances. Low airburst, typically about 10 metres, was used with HE. The height of burst with shrapnel depended on the angle of descent, but for optimal use it was a few tens of metres. When the shell was fired the shock of firing set back a detonator onto a firing pin, which ignited the powder ring, when the burn reached the fuze setting it flashed through a hole into the fuze magazine, which then ignited the bursting charge in the shell.
If the shell contained HE then the fuze had a gaine that converted the powder explosion into a detonation powerful enough to detonate the HE. The problem with igniferous fuzes was that they were not very precise and somewhat erratic, but good enough for flat trajectory shrapnel ranges were relatively short by later standards or high bursting carrier shells.
While improvements in powder composition helped, there were several complex factors that prevented a high degree of regularity in the field. Britain in particular encountered great difficulty in achieving consistency early in World War I and with its attempts to use its by-then obsolescent gunpowder-train time fuzes for anti-aircraft fire against German bombers and airships which flew at altitudes up to 20, feet. It was then discovered that standard gunpowder burned differently at differing altitudes, and the problem was then rectified to some extent by specially designed fuzes with modified gunpowder formulations.
Residual stocks of igniferous fuzes lasted for many years after World War 2 with smoke and illuminating shells. It contained a spring clock with an extra rapid cylinder escapement giving 30 beats per second. These were less erratic and more precise than igniferous fuzes, critical characteristics as gun ranges increased. Between the wars five or six different mechanical mechanisms were developed in various nations.
Mechanical time fuzes were just about good enough to use with field artillery to achieve the effective HE height of burst of about 10 metres above the ground. However, 'good enough' usually meant '4 in the air and 2 on the ground'. This fuze length was extremely difficult to predict with adequate accuracy, so the height of burst almost always had to be adjusted by observation.
The benefits of a fuze that functioned when it detected a target in proximity are obvious, particularly for use against aircraft. These used a photo-electric fuze. During a private venture initiative by Pye Ltd, a leading British wireless manufacturer, worked on the development of a radio proximity fuze.
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. For the first 18 months or so proximity fuzes were restricted to anti-aircraft use to ensure that none were retrieved by the enemy and copied.
They were finally released for field artillery use in December in Europe. While they were not perfect and bursts could still be erratic due to rain, they were a vast improvement on mechanical time in delivering a very high proportion of bursts at the required 10 metre height. However, VT fuzes went far deeper into the shell than other fuzes because they had a battery that was activated by the shock of firing. This meant the fuze recess had to be deeper, so to enable shorter non-VT fuzes the deep recess was filled with removable supplementary HE canisters.
After the war the next generation of proximity fuze included a mechanical timer to switch on the fuze a few seconds before it was due at the target. While working for a defense contractor in the mids, Soviet spy Julius Rosenberg stole a working model of an American proximity fuze and delivered it to the Soviet intelligence. Working with Western Electric Company and Raytheon Company , miniature hearing-aid tubes were modified to withstand this extreme stress. The United States Navy accepted that failure rate. A simulated battle conditions test was started on 12 August The tests were to be conducted over two days, but the testing stopped when drones were destroyed early on the first day.
The three drones were destroyed with just four projectiles. A particularly successful application was the 90mm shell with VT fuze with the SCR automatic tracking radar and the M-9 electronic fire control computer. The combination of these three inventions was successful in shooting down many V-1 flying bombs aimed at London and Antwerp, otherwise difficult targets for anti-aircraft guns due to their small size and high speed.
In Germany, more than 30 approaches to proximity fuze development were under way, but none saw service. A German neon lamp tube and a design of a prototype proximity fuze based on capacitive effects was received by British Intelligence in mid November By the end of the war, only one was actually in production, a complicated radio proximity fuze for rockets and bombs but not designed to withstand the acceleration of artillery shells.
The Allied fuze used constructive and destructive interference to detect its target. When the target was far away, it would reflect little of the oscillator's energy back to the fuze and have almost no effect on the circuit. When a target was nearby, it would reflect a significant portion of the oscillator's signal back to the fuze.
The amplitude of the reflected signal indicated the closeness of the target. If the reflected signal were in phase, the oscillator amplitude would increase and the oscillator's plate current would also increase. If the reflected signal were out of phase, then the plate current would decrease. The distance between the fuze and the target is 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 changes rapidly, then the phase relationship also changes rapidly.
The signals are in-phase one instant and out-of-phase a few hundred microseconds later. The result is a heterodyne beat frequency that indicates the velocity difference.
Viewed another way, the received signal frequency is doppler shifted from the oscillator frequency by the relative motion of the fuze and target. Consequently, a low frequency signal corresponding to the frequency difference develops at the oscillator's plate terminal. Two additional amplifiers detected and filtered this low frequency signal.
If the amplified beat frequency signal is large enough indicating a nearby object , then it triggers the 4th tube a gas-filled thyratron ; the thyratron conducts a large current that sets off the electrical detonator. There were many shock hardening techniques including planar electrodes and packing the components in wax and oil to equalize the stresses.
The designation VT means variable time. Shumaker, Director of the Bureau of Ordnance's Research and Development Division, coined the term to be descriptive without hinting at the technology. 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, test firings were conducted from to First large scale production of tubes for the new fuzes  was at a General Electric plant in Cleveland, Ohio formerly used for manufacture of Christmas-tree lamps.
By , a large proportion of the American electronics industry concentrated on making the fuzes. This permitted the purchase of over 22 million fuzes for approximately one billion dollars. There were also over two thousand suppliers and subsuppliers, ranging from powder manufacturers to machine shops. Vannevar Bush , head of the U. 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 Also in , 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, dud shells fell into the sea, safely out of reach of capture. A minor problem encountered by the British was that the fuses were sensitive enough to detonate the shell if it passed too close to a seagull and a number of seagull "kills" were recorded. The Pentagon refused to allow the Allied field artillery use of the fuzes in , although the United States Navy fired proximity-fuzed anti-aircraft shells during the July invasion of Sicily. They made the Allied heavy artillery far more devastating, as all the shells now exploded just before hitting the ground.
The effectiveness of the new VT fused shells exploding in mid-air, on exposed personnel, caused a minor mutiny when German soldiers started refusing orders to move out of their bunkers during an artillery attack. Patton said that the introduction of the proximity fuze required a full revision of the tactics of land warfare. It was at this time that the Germans also abandoned their magnetron and microwave radar development teams and programs. Many other advanced and experimental programs also suffered. Upon resumption of research and testing by Rheinmetall in the Germans managed to develop and test fire several hundred working prototypes before the war ended.
The device described in World War II patent  works as follows: As the shell approaches a reflecting object, an interference pattern is created. This pattern changes with shrinking distance: This signal is sent through a band pass filter , amplified, and triggers the detonation when it exceeds a given amplitude.
Optical sensing was developed in , and patented in Great Britain in , 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 photo cell. When the cell current changed a certain amount in a certain time interval, the detonation was triggered. Some modern air-to-air missiles e. 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 back to the missile, where detectors sense it and detonate the warhead.
Acoustic sensing used a microphone in a missile.
The characteristic frequency of an aircraft engine is filtered and triggers the detonation. This principle was applied in British experiments with bombs, anti-aircraft missiles, and airburst shells circa Later it was applied in German anti-aircraft missiles, which were mostly still in development when the war ended. The British used a Rochelle salt microphone and a piezoelectric device to trigger a relay to detonate the projectile or bomb's explosive. Naval mines can also use acoustic sensing with an acoustic fuze , with modern versions able to be programmed to "listen" for the signature of a specific ship.
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 minesweepers or by magnetic induction loops fitted to aircraft or towed buoys. The designation "VT" is often said to refer to "variable time".