Fuze In military munition s , a fuze is the part of the device that initiates function . The term " fuze " is used to indicate a sophisticated ignition device incorporating mechanical and / or electronic components e . g . a proximity fuze for an M107 artillery shell , magnetic / acoustic fuze on a sea mine , spring - loaded grenade fuze , pencil detonator or anti - handling device . Most English - language countries use the " z " spelling to distinguish between simple burning fuses and more complicated munition fuzes , which contain mechanical and / or electronic components , although historically this has by no means been a hard - and - fast rule , with " fuse " often used as the spelling in many sources , as the example " hand grenade fuse " shows . The relative complexity of even the earliest fuze designs ( dating from circa 1915 ) can be seen in the cutaway diagrams at the end of this article . Modern fuzes for " smart weapon s " are invariably computerised ( " i . e . , " incorporate microprocessors or gate array s ) . Description . A fuze is a device used in munition s which is designed to detonate , or to set forces into action to ignite , detonate or deflagrate , the charge ( or primer ) under specified conditions . In contrast to a simple pyrotechnic fuse , a munitions fuze always has some form of safety / arming mechanism , designed to protect the user from premature or accidental detonation . A munition fuze assembly may contain only the electronic or mechanical elements necessary to signal or actuate the detonator , but some fuzes contain a small amount of primary explosive to initiate the detonation . Fuze assemblies for large explosive charges may include an explosive booster . Fuze categorization by munition type . The situation of usage and the characteristics of the munition it is intended to activate affect the fuze design e . g . its safety and actuation mechanisms . Artillery fuzes . Artillery fuzes are tailored to function in the special circumstances of artillery projectiles , the relevant factors are the projectile ' s initial rapid acceleration , high velocity and usually rapid rotation , which affect both safety and arming requirements and options , and the target may be moving or stationary . Artillery fuzes may be initiated by a timer mechanism , impact or detection of proximity to the target , or a combination of these . Hand grenade fuzes . Requirements for a hand grenade fuze are defined by the projectile ' s small size and slow delivery over a short distance . This necessitates manual arming before throwing as the grenade has insufficient initial acceleration for arming to be driven by " setback " and no rotation to drive arming by centrifugal force . Aerial bomb fuzes . These are also referred to as " pistols " . The main design consideration is that the projectile is large and accelerating vertically downwards and may or may not be rotating relatively slowly . Landmine fuzes . The main design consideration is that the bomb the fuze is intended to actuate is stationary , and the target itself is moving in making contact . Naval mine fuzes . Relevant design factors are that the mine may be static or moving downward through the water , and the target is typically moving on or below the water surface , usually above the mine . Fuze categorization by activation mechanism . Time fuzes . Time fuzes detonate after a set period of time by using one or more combinations of mechanical , electronic , pyrotechnic or even chemical timers . Depending on the technology used , the device may self - destruct ( or render itself safe without detonation ) some seconds , minutes , hours , days , or even months after being deployed . Early artillery time fuzes were nothing more than a hole filled with gunpowder leading from the surface to the centre of the projectile . The flame from the burning of the gunpowder propellant ignited this " fuze " on firing , and burned through to the centre during flight , then igniting or exploding whatever the projectile may have been filled with . By the 19th century devices more recognisable as modern artillery " fuzes " were being made of carefully selected wood and trimmed to burn for a predictable time after firing . These were still typically fired from smoothbore muzzle - loaders with a relatively large gap between the shell and barrel , and still relied on flame from the gunpowder propellant charge escaping past the shell on firing to ignite the wood fuze and hence initiate the timer . In the mid - to - late 19th century adjustable metal time fuzes , the fore - runners of today ' s time fuzes , containing burning gunpowder as the delay mechanism became common , in conjunction with the introduction of rifled artillery . Rifled guns introduced a tight fit between shell and barrel and hence could no longer rely on the flame from the propellant to initiate the timer . The new metal fuzes typically use the shock of firing ( " setback " ) and / or the projectiles ' s rotation to " arm " the fuze and initiate the timer : hence introducing a safety factor previously absent . During World War I mechanical i . e . clockwork time fuzes were introduced for artillery , notably by Germany , and some variants are still in use . As late as World War I some countries were still using hand - grenades with simple Black match fuses much like those of modern fireworks : the infantryman lit the fuse before throwing the grenade and hoped the fuse burned for the several seconds intended . These were soon superseded in 1915 by the Mills bomb , the first modern hand grenade with a relatively safe and reliable time fuze initiated by pulling out a safety pin and releasing an arming handle on throwing . Modern time fuzes often use an electronic delay system . Impact fuzes . Impact , percussion or contact fuzes detonate when their forward motion rapidly decreases , typically on physically striking an object such as the target . The detonation may be instantaneous or deliberately delayed to occur a preset fraction of a second after penetration of the target . An instantaneous " Superquick " fuze will detonate instantly on the slightest physical contact with the target . A fuze with a graze action will also detonate on change of direction caused by a slight glancing blow on a physical obstruction such as the ground . Impact fuzes in artillery usage may be mounted in the shell nose ( " point detonating " ) or shell base ( " base detonating " ) . Proximity fuzes . Proximity fuze s cause a missile warhead or other munition ( e . g . air - dropped bomb or sea mine ) to detonate when it comes within a certain pre - set distance of the target , or vice versa . Proximity fuzes utilize sensors incorporating one or more combinations of the following : radar , active sonar , passive acoustic , infrared , magnetic , photoelectric , seismic or even television cameras . These may take the form of an anti - handling device designed specifically to kill or severely injure anyone who tampers with the munition in some way e . g . lifting or tilting it . Regardless of the sensor used , the pre - set triggering distance is calculated such that the explosion will occur sufficiently close to the target that it is either destroyed or severely damaged . Remote detonators . Remote detonator s use wire s or radio waves to remotely command the device to detonate . Barometric fuzes . Barometric fuze s cause a bomb to detonate at a certain pre - set altitude above sea level by means of a radar , barometric altimeter or an infrared rangefinder . Combination fuzes . A fuze assembly may include more than one fuze in series or parallel arrangements . The RPG - 7 usually has an impact ( PIBD ) fuze in parallel with a 4 . 5 second time fuze ; so detonation occurs on impact , but not later than after 4 . 5 seconds . Military weapons containing explosives have fuzing systems including a series time fuze to ensure that they do not initiate ( explode ) prematurely within a danger distance of the munition launch platform . In general , the munition has to travel a certain distance , wait for a period of time ( via clockwork , electronic or even a chemical delay ) , or have some form of arming pin / plug removed . Only when these processes have occurred will the arming process of the series time fuze be complete . Mines often have a parallel time fuze to detonate and destroy the mine after a pre - determined period to minimize casualties after the anticipated duration of hostilities . Detonation of modern naval mine s may require simultaneous detection of a series arrangement of acoustic , magnetic , and / or pressure sensors to complicate mine - sweeping efforts . Fuze safety / arming mechanisms . The multiple safety / arming features in the M734 mortar fuze are representative of the sophistication of modern electronic fuzes . Safety / arming mechanisms can be as simple as the spring - loaded safety levers on M67 or RGD - 5 grenade fuzes , which will not initiate the explosive train so long as the pin is kept in the grenade , or the safety lever is held down on a pinless grenade . Alternatively , it can be as complex as the electronic timer - countdown on an influence sea mine , which gives the vessel laying it sufficient time to move out of the blast zone before the magnetic or acoustic sensors are fully activated . In modern artillery shell s , most fuzes incorporate several safety features to prevent a fuze arming before it leaves the gun barrel . These safety features may include arming on " setback " or by centrifugal force , and often both operating together . Set - back arming uses the inertia of the accelerating artillery shell to remove a safety feature as the projectile accelerates from rest to its in - flight speed . Rotational arming requires that the artillery shell reach a certain rpm before centrifugal force s cause a safety feature to disengage or move an arming mechanism to its armed position . Artillery shells are fired through a rifled barrel , which forces them to spin during flight . In other cases the bomb , mine or projectile has a fuze that prevents accidental initiation e . g . stopping the rotation of a small propeller ( unless a lanyard pulls out a pin ) so that the striker - pin cannot hit the detonator even if the weapon is dropped on the ground . These types of fuze operate with aircraft weapons , where the weapon may have to be jettisoned over " friendly " territory to allow a damaged aircraft to continue to fly . The crew can choose to jettison the weapons " safe " by dropping the devices with safety pins still attached , or drop them " live " by removing the safety pins as the weapons leave the aircraft . Aerial bombs and depth charge s can be " nose " and " tail " fuzed using different detonator / initiator characteristics so that the crew can choose which effect fuze will suit target conditions that may not have been known before the flight . The arming switch is set to one of " safe " , " nose " , or " tail " at the crew ' s choice . Base fuzes are also used by artillery and tanks for shells of the ' squash head ' type . Some types of armour piercing shells have also used base fuzes , as have nuclear artillery shells . The most sophisticated fuze mechanisms of all are those fitted to nuclear weapons , and their safety / arming devices are correspondingly complex . In addition to PAL protection , the fuzing used in nuclear weapons features multiple , highly sophisticated environmental sensors e . g . sensors requiring highly specific acceleration and deceleration profiles before the warhead can be fully armed . The intensity and duration of the acceleration / deceleration must match the environmental conditions which the bomb / missile warhead would actually experience when dropped or fired . Furthermore , these events must occur in the correct order . Note : some fuzes , e . g . those used in air - dropped bombs and landmines may contain anti - handling device s specifically designed to kill bomb disposal personnel . The technology to incorporate booby - trap mechanisms in fuzes has existed since at least 1940 e . g . the German ZUS40 anti - removal bomb fuze . Reliability . A fuze must be designed to function appropriately considering relative movement of the munition with respect to its target . The target may move past stationary munitions like land mine s or naval mines ; or the target may be approached by a rocket , torpedo , artillery shell , or air - dropped bomb . Timing of fuze function may be described as " optimum " if detonation occurs when target damage will be maximized , " early " if detonation occurs prior to optimum , " late " if detonation occurs past optimum , or " dud " if the munition fails to detonate . Any given batch of a specific design may be tested to determine the anticipated percentage of " early " , " optimum " . " late " , and " dud " expected from that fuze installation . Combination fuze design attempts to maximize " optimum " detonation while recognizing dangers of " early " fuze function ( and potential dangers of " late " function for subsequent occupation of the target zone by friendly forces or for gravity return of anti - aircraft munitions used in defense of surface positions . ) Series fuze combinations minimize " early " function by detonating at the latest activation of the individual components . Series combinations are useful for safety arming devices , but increase the percentage of " late " and " dud " munitions . Parallel fuze combinations minimize " duds " by detonating at the earliest activation of individual components , but increase the possibility of premature " early " function of the munition . Sophisticated military munition fuzes typically contain an arming device in series with a parallel arrangement of sensing fuzes for target destruction and a time fuze for self - destruction if no target is detected .