A contact fuze, impact fuze, percussion fuze or direct-action (D.A.) fuze (UK) is the fuze that is placed in the nose of a bomb or shell so that it will detonate on contact with a hard surface.
Many impacts are unpredictable: they may involve a soft surface, or an off-axis grazing impact. The pure contact fuze is often unreliable in such cases and so a more sensitive graze fuze or inertia fuze is used instead. The two types are often combined in the same mechanism. [1]
The British Army's first useful impact fuze for high-explosive shells was the Fuze No. 106 of World War I. (illus.) This used a simple protruding plunger or striker at the nose, which was pushed back to drive a firing pin into the detonator. Its ability to burst immediately at ground level was used to clear the barbed wire entanglements of no man's land, rather than burying itself first and leaving a deep, but useless, crater. The striker was protected by a safety cap that was removed before loading, but there was no other safety mechanism.
The simplest form of artillery contact fuze is a soft metal nose to the shell, filled with a fulminating explosive such as lead azide. An example is the British World War II Fuze, Percussion, D.A., No. 233 [2] ('direct action') The primary explosive transmits its detonation to an explosive booster within the fuze, then in turn to the main charge of the shell. As an artillery shell lands with a considerable impact, the "soft" nose may be made robust enough to be adequately safe for careful handling, without requiring any protection cap or safety mechanism. As a matter of normal practice though, fuzes and shells are transported separately and the fuze is only installed shortly prior to use. These simple contact fuzes are generally used for anti-tank shells, rather than high-explosive.
A more sophisticated fuze is the double-acting fuze, which is sensitive to both contact and grazing. [note 1] An example of such a double-acting fuze is the British WW II Fuze, D.A. and percussion, No. 119 [1] This fuze uses a nose striker, as for the original No. 106, but is rather more complex with an added inertia mechanism for grazing impacts and also three automatic safety devices. Simple contact impacts drive the striker back into the detonating pellet, as before. Graze impacts trigger the inertia mechanism, where instead the pellet in a heavy carrying plug travels forwards onto the striker. The striker is protected in storage by a nose safety cap. Normally this is removed before loading, but it may also be left in place if the target is behind cover. This reduces the sensitivity of the striker to light impacts through vegetation, but the fuze will still function through the inertia mechanism, or through a hard impact. Three safety devices are provided, one released by inertia during firing, which then unlocks a second that is released by centrifugal force of the spinning shell. These are mechanical locks that prevent the striker contacting the pellet. A third device is a centrifugal shutter that initially blocks propagation from the detonator pellet to the booster explosive.
Most artillery contact fuzes act immediately, although some may have a delay. [3] This allows a high-explosive or semi-armour-piercing shell to penetrate a wall before exploding, thus achieving the most damage inside the building. Where a shell is used against strong armour and requires all of its explosive power merely to penetrate, a delay is not appropriate. Most such delayed fuzes are thus switchable to a "superquick" or immediate mode. [3]
Timed fuzes are used for airbursts. They take their delay time (½ second or longer) from firing, not from impact. These fuzes may also offer a contact fuzed ability. [4] As this type of fuze is complex and more sensitive, they usually have a deliberate safing mechanism such as an arming wire that must be removed before use.
Fuzes for air-dropped bombs have generally used an internally mounted inertia fuze, triggered by the sudden deceleration on impact. Owing to the risk of an aircraft crash, or even the need to land with an undropped bomb still on board, these are protected by sophisticated safety systems so that the fuze can only be triggered after it has been dropped intentionally.
The German Stachelbombe (nose-spike bomb) or stabo of WWII was a standard bomb, from 50 kg to 500 kg, modified for use from low altitude. [5] To avoid the risk of ricochet from the ground, a nose spike was fitted to penetrate first and anchor the bomb against bouncing — without this, there was a risk of the dropping aircraft not only missing the target, but also being damaged by its own weapon. As the German electric fuzes had an arming delay after dropping, and the bombs were dropped at such low altitude as to leave insufficient time for this to arm, they were also sometimes fitted with additional contact fuzes on the tips of these nose spikes.
Similar devices were employed by Soviet forces, in a similar ground attack role using the Il-2 Sturmovik.
Notable examples of air-dropped bombs that did use contact fuzes include the Fat Man atomic bomb dropped on Nagasaki. The bomb was intended for air burst detonation and was fitted with both radar height-finding and barometric fuzes. As the device was so secret, and the risk of informative fragments or plutonium being recovered after a failed drop was considered to be unacceptable, it was fitted with supplementary contact fuzes that were only intended to destroy the weapon beyond recognition. Four AN-219 piezo-electric impact fuzes were fitted to the nose of the bomb casing. [6]
The BLU-82 was a large conventional explosive bomb, used to make helicopter landing clearings in forests. The intended fusing was an extremely low air burst of only a few feet, so as to maximize the clearance effect and minimize cratering. The fuze was a mechanical impact fuze on a 38-inch (97 cm) nose spike.
The contact fuze is set off when a series of connected crush switches that are placed on the exterior nose of the ordnance device make contact with the ground. The contact with solid ground activates the interior firing circuits which leads to the detonation of the ordnance device. A cone shaped cover over the device prevents premature detonation while the device is being loaded and carried to the desired location by aircraft.
Armour-piercing ammunition (AP) is a type of projectile designed to penetrate armour protection, most often including naval armour, body armour, and vehicle armour.
A shell, in a military context, is a projectile whose payload contains an explosive, incendiary, or other chemical filling. Originally it was called a bombshell, but "shell" has come to be unambiguous in a military context. A shell can hold a tracer.
In an explosive, pyrotechnic device, or military munition, a fuse is the part of the device that initiates function. In common usage, the word fuse is used indiscriminately. However, when being specific, the term fuse describes a simple pyrotechnic initiating device, like the cord on a firecracker whereas the term fuze is used when referring to a more sophisticated ignition device incorporating mechanical and/or electronic components, such as a proximity fuze for an M107 artillery shell, magnetic or acoustic fuze on a sea mine, spring-loaded grenade fuze, pencil detonator, or anti-handling device.
A firing pin or striker is a part of the firing mechanism of a firearm that impacts the primer in the base of a cartridge and causes it to fire. In firearms terminology, a striker is a particular type of firing pin where a compressed spring acts directly on the firing pin to provide the impact force rather than it being struck by a hammer.
The Butterfly Bomb was a German 2-kilogram (4.4 lb) anti-personnel submunition used by the Luftwaffe during the Second World War. It was so named because the thin cylindrical metal outer shell which hinged open when the bomblet deployed gave it the superficial appearance of a large butterfly. The design was very distinctive and easy to recognise. SD 2 bomblets were not dropped individually, but were packed into containers holding between 6 and 108 submunitions e.g. the AB 23 SD 2 and AB 250-3 submunition dispensers. The SD 2 submunitions were released after the container was released from the aircraft and had burst open. Because SD 2s were always dropped in groups the discovery of one unexploded SD 2 was a reliable indication that others had been dropped nearby. This bomb type was one of the first cluster bombs ever used in combat and it proved to be a highly effective weapon. The bomb containers that carried the SD 2 bomblets and released them in the air were nicknamed the "Devil's Eggs" by Luftwaffe air and ground crew.
An air burst or airburst is the detonation of an explosive device such as an anti-personnel artillery shell or a nuclear weapon in the air instead of on contact with the ground or target. The principal military advantage of an air burst over a ground burst is that the energy from the explosion, including any shell fragments, is distributed more evenly over a wider area; however, the peak energy is lower at ground zero.
The British No. 69 was a hand grenade developed and used during the Second World War. It was adopted into service due to the need for a grenade with smaller destructive radius than the No. 36M "Mills bomb". This allowed the thrower to use a grenade even when there was little in the way of defensive cover. In contrast, the much greater destructive radius of the Mills bomb than its throwing range forced users to choose their throwing point carefully, in order to ensure that they would not be wounded by the shrapnel explosion of their own grenade.
The M734 multi-option fuze is a rangefinder and collision detection system used on 60 mm, 81 mm, and 120 mm mortar shells as a trigger to detonate the shells at the most damaging heights of burst when combating four types of battlefield threats:
The Ordnance QF 75 mm, abbreviated to OQF 75 mm, was a British tank gun of the Second World War. It was obtained by boring out the Ordnance QF 6-pounder 57 mm anti-tank gun to 75 mm, to give better performance against infantry targets similarly to the 75 mm M3 gun fitted to the American Sherman tank. The QF came from "quick-firing", referring to the use of ammunition where the shell has a fixed cartridge. The gun was also sometimes known as ROQF from Royal Ordnance Quick-Firing.
The VS-50 is a circular plastic-cased anti-personnel blast mine that entered production in 1985. It was formerly made by the now-defunct Valsella Meccanotecnica SpA, an Italian high-tech defence company specialized in area denial systems. The company also the made the Valmara 69, and was one of the first to implement plastic construction for landmines. The VS-50's design is similar to that of the TS-50 and VS-MK2 mines. It is blast resistant and can be used in a minimum metal configuration. Though unlikely to kill, its explosive charge is quite sufficient to destroy the victim's foot, being capable of penetrating 5 mm of mild steel leaving an 80 mm-diameter hole.
An anti-handling device is an attachment to or an integral part of a landmine or other munition such as some fuze types found in general-purpose air-dropped bombs, cluster bombs and sea mines. It is designed to prevent tampering or disabling, or to target bomb disposal personnel. When the protected device is disturbed, it detonates, killing or injuring anyone within the blast area. There is a strong functional overlap of booby traps and anti-handling devices.
The SC 250 was an air-dropped general purpose high-explosive bomb built by Germany during World War II and used extensively during that period. It could be carried by almost all German bomber aircraft, and was used to notable effect by the Junkers Ju 87 Stuka. The bomb's weight was about 250 kg, from which its designation was derived.
In military munitions, a fuze is the part of the device that initiates its function. In some applications, such as torpedoes, a fuze may be identified by function as the exploder. The relative complexity of even the earliest fuze designs can be seen in cutaway diagrams.
A grenade is an explosive weapon typically thrown by hand, but can also refer to a shell shot from the muzzle of a rifle or a grenade launcher. A modern hand grenade generally consists of an explosive charge ("filler"), a detonator mechanism, an internal striker to trigger the detonator, an arming safety secured by a transport safety. The user removes the transport safety before throwing, and once the grenade leaves the hand the arming safety gets released, allowing the striker to trigger a primer that ignites a fuze, which burns down to the detonator and explodes the main charge.
An artillery fuze or fuse is the type of munition fuze used with artillery munitions, typically projectiles fired by guns, howitzers and mortars. A fuze is a device that initiates an explosive function in a munition, most commonly causing it to detonate or release its contents, when its activation conditions are met. This action typically occurs a preset time after firing, or on physical contact with or detected proximity to the ground, a structure or other target. Fuze, a variant of fuse, is the official NATO spelling.
The number 106 fuze was the first British instantaneous percussion artillery fuze, first tested in action in late 1916 and deployed in volume in early 1917.
The Stielgranate 41 was a German shaped charge, fin-stabilized shell, used with the 3.7 cm Pak 36 anti-tank gun to give it better anti-tank performance.
The Type 3 81 mm mortar is a smooth bore, muzzle-loading 81 mm (3.19 in) infantry weapon used by the Imperial Japanese Army during World War II. The Type 3 designation was given to this gun as it was accepted in the 3rd year of Emperor Taishō's reign (1914).
The SC 50 or cylindrical explosive bomb in English was a family of general-purpose bombs used by the Luftwaffe during World War II.
The BDC 10 was a cluster bomb used by the Luftwaffe during World War II.