Shell ( projectile ) A shell is a payload - carrying projectile which , as opposed to shot , contains an explosive or other filling , though modern usage sometimes includes large solid projectiles properly termed shot ( AP , APCR , APCNR , APDS , APFSDS and proof shot ) . Solid shot may contain a pyrotechnic compound if a tracer or spotting charge is used . Originally it was called a " bombshell " , but " shell " has come to be unambiguous in a military context . " Bombshell " is still used figuratively to refer to a shockingly unexpected happening or revelation . All explosive - and incendiary - filled projectiles , particularly for mortars , were originally called " grenades " , derived from the pomegranate , whose seeds are similar to grains of powder . Words cognate with " grenade " are still used for an artillery or mortar projectile in some European languages . Shells are usually large - calibre projectiles fired by artillery and combat vehicle s ( including tank s ) , and warship s . Shells usually have the shape of a cylinder topped by an ogive - shaped nose for good aerodynamic performance , possibly with a tapering base ; but some specialized types are quite different . History . Solid cannonballs ( “ shot ” ) did not need a fuse , but hollow munitions ( “ shells ” ) filled with something such as gunpowder to fragment the ball , needed a fuse , either impact ( percussion ) or time . Percussion fuses with a spherical projectile presented a challenge because there was no way of ensuring that the impact mechanism hit the target . Therefore shells needed a time fuse that was ignited before or during firing and burnt until the shell reached its target . Early reports of shells include Venetian use at Jadra in 1376 and shells with fuses at the 1421 siege of St Boniface in Corsica . These were two hollowed hemispheres of stone or bronze held together by an iron hoop . Written evidence for early explosive shells in China appears in the early Ming Dynasty ( 1368 – 1644 ) Chinese military manual " Huolongjing " , compiled by Jiao Yu ( fl . 14th to early 15th century ) and Liu Ji ( 1311 – 1375 ) sometime before the latter ' s death , a preface added by Jiao in 1412 . As described in their book , these hollow , gunpowder - packed shells were made of cast iron . Yi jang - son made in the reign of Seonjo of Joseon . Bigyukjincheonroi is a time shell that consisted of wooden tube wound with time fuse made of thread , iron scrap and cap . Its time fuse can be set the time by length of thread . It was used in Japanese invasions of Korea . They were usually fired from the family of " wan - gu " ( Hangul : 완구 ; Hanja : 碗口 ; literally " bowl - mouth " ) mortars . An early problem was that until 1672 there was no means of measuring the time precisely enough — clockwork fuses did not yet exist . The burning time of the powder fuse was subject to considerable trial and error . Early powder burning fuses had to be loaded fuse down to be ignited by firing or a portfire put down the barrel to light the fuse . Other shells were wrapped in bitumen cloth which would ignite during the firing and in turn ignite a powder fuse . However , by the 18th Century it was discovered that the fuse towards the muzzle could be lit by the flash through the windage between shell and barrel . Nevertheless , shells came into regular use in the 16th Century , for example a 1543 English mortar shell filled with ' wildfire ' . About 1700 shells began to be employed for horizontal fire from howitzers with a small propelling charge and in 1779 experiments demonstrated that they could be used from guns with heavier charges . They became usual with field artillery early in the 19th Century . By this time shells were usually cast iron , but bronze , lead , brass and even glass were tried . See the article on Artillery fuse for more information . The word " bomb " ( and its cognates in other languages , such as Spanish " bomba " ) encompassed them at the time , as heard in the lyrics of " The Star - Spangled Banner " ( " the bombs bursting in air " ) , although today that sense of " bomb " is obsolete . Cast - iron spherical common shell ( so named because they were used against " common " [ usual ] targets ) were in use up to 1871 . Typically the thickness of the metal body was about 1 / 6 their diameter and they were about 2 / 3s the weight of solid shot of the same calibre . In order to ensure that shells were loaded with their fuses towards the muzzle they were attached to wooden bottoms called ' sabots ' . In 1819 a committee of British artillery officers recognised that they were essential stores and in 1830 Britain standardised sabot thickness as half inch . The sabot also intended to reduce jamming during loading and the rebounding of the shell as it traveled along the bore on discharge . Mortar shells were not fitted with sabot s . Rifling was invented by Jaspard Zoller , a Viennese gun maker at the end of the 15th Century , and it was realised that twisted rifling to spin an elongated projectile would greatly improve its accuracy . This was known to artillerists but its application to artillery was beyond the available technology until around the mid 19th Century . English inventor notable Armstrong , Whitworth and Lancaster [ ? ] and the latter ' s rifled guns were used in the Crimean War . Armstrong ' s rifled breech - loading cannon was a key innovation and adopted for British service in 1859 . Also in the 1850s rifled guns were developed by Major Cavelli in Italy , Baron Wahrendorff and Krupp in Germany and the Wiard gun in the United States . However , rifled barrels required some means of engaging the shell with the rifling . Lead coated shells were used with Armstrong guns , but were not satisfactory so studded projectiles were adopted . However these did not seal the gap between shell and barrel . Wads at the shell base were tried , without success , in 1878 the British adopted a copper ' gas - check ' at the base of their studded projectiles , and in 1879 tried a rotating gas check to replace the studs , leading to the 1881 automatic gas - check . This was soon followed by the Vavaseur copper driving band as part of the projectile . The driving band rotated the projectile , centred it in the bore and prevented gas escaping forwards . A driving band has to be soft but tough enough to prevent stripping by rotational and engraving stresses . Copper is generally most suitable but cupro nickel or gilding metal are also used . The first pointed armour piercing shell was introduced by Major Palliser in 1863 , it was made of chilled cast iron with an ogival head of 1 calibres radius . However , during 1880 – 1890 steel shells and armour began to appear and it was realised that steel bodies for explosive filled shells had advantages - better fragmentation and resistance to the stresses of firing . These were cast and forged steel . Shells have never been limited to an explosive filling . An incendiary shell was invented by Valturio in 1460 . The carcass was invented in 1672 by a gunner serving Christoph van Galen , Prince Bishop of Munster , initially oblong in an iron frame or carcass ( with poor ballistic properties ) it evolved into a spherical shell . Their use continued well into the 19th Century . In 1857 the British introduced an incendiary shell ( Martin ' s ) filled with molten iron , which replaced red hot shot used against ships , most notably at Gibraltar in 1782 . Two patterns of incendiary shell were used by the British in World War 1 , one designed for use against Zeppelins . Similar to incendiary shells were star shells , designed for illumination rather than arson . Sometimes called lightballs they were in use from the 17th Century onwards . The British adopted parachute lightballs in 1866 for 10 , 8 and 5 inch calibres . The 10 - inch wasn ' t officially declared obsolete until 1920 . Smoke balls also date back to the 17th Century , British ones contained a mix of saltpetre , coal , pitch , tar , resin , sawdust , crude antimony and sulphur . They produced a ' noisome smoke in abundance that is impossible to bear ' . In the 19th Century British service they were made of concentric paper with thickness about 1 / 15th of total diameter and filled with powder , saltpetre , pitch , coal and tallow . They were used to ' suffocate or expel the enemy in casemates , mines or between decks ; for concealing operations ; and as signals . During the First World War , shrapnel shell s and explosive shells inflicted terrible casualties on infantry , accounting for nearly 70 % of all war casualties and leading to the adoption of steel helmet s on both sides . Shells filled with poison gas were used from 1917 onwards . Frequent problems with shells led to many military disasters when shells failed to explode , most notably during the 1916 Battle of the Somme . Sizes . The calibre of a shell is its diameter . Depending on the historical period and national preferences , this may be specified in millimetres , centimetres , or inches . The length of gun barrels for large cartridges and shells ( naval ) is frequently quoted in terms of the ratio of the barrel length to the bore size , also called calibre . For example , the 16 " / 50 caliber Mark 7 gun is 50 calibers long , that is , 16 " ×50 = 800 " = 66 . 7 feet long . Some guns , mainly British , were specified by the weight of their shells ( see below ) . Due to manufacturing difficulties the smallest shells commonly used are around 20 mm calibre , used in aircraft cannon and on armoured vehicles . Smaller shells are only rarely used as they are difficult to manufacture and can only have a small explosive charge . The largest shells ever fired were those from the German super - railway gun s , Gustav and Dora , which were 800 mm ( 31 . 5 " ) in calibre . Very large shells have been replaced by rocket s , guided missile , and bombs , and today the largest shells in common use are 155 mm ( 6 . 1 " ) . Gun calibres have standardized around a few common sizes , especially in the larger range , mainly due to the uniformity required for efficient military logistics . Shells of 105 , 120 , and 155 mm diameter are common for NATO forces ' artillery and tank gun s . Artillery shells of 122 , 130 and 152 mm , and tank gun ammunition of 100 , 115 , or 125 mm calibre remain in use in Eastern Europe and China . Most common calibres have been in use for many years , since it is logistically complex to change the calibre of all guns and ammunition stores . The weight of shells increases by and large with calibre . A typical 150 mm ( 5 . 9 " ) shell weighs about 50 kg , a common 203 mm ( 8 " ) shell about 100 kg , a concrete demolition 203 mm ( 8 " ) shell 146 kg , a 280 mm ( 11 " ) battleship shell about 300 kg , and a 460 mm ( 18 " ) battleship shell over 1500 kg . The Schwerer Gustav supergun fired 4 . 8 and 7 . 1 tonne shells . Old - style British classification by weight . During the 19th Century the British adopted a particular form of designating artillery . Guns were designated by nominal standard projectile weight while Howitzers were designated by barrel calibre . British Guns and their ammunition were designated in pounds , e . g . , as " two - pounder " shortened to " 2 - pr " or " 2 - pdr " . Usually this referred to the actual weight of the standard projectile ( shot , shrapnel or HE ) , but , confusingly , this was not always the case . Some were named after the weights of obsolete projectile types of the same calibre , or even obsolete types that were considered to have been functionally equivalent . Also , projectiles fired from the same gun , but of non - standard weight , took their name from the gun . Thus , conversion from " pounds " to an actual barrel diameter requires consulting a historical reference . Since the creation of NATO new British guns are designated by calibre . Types . There are many different types of shells . The principal ones include : High - explosive . The most common shell type is high explosive , commonly referred to simply as HE . They have a strong steel case , a bursting charge , and a fuse . The fuse detonates the bursting charge which shatters the case and scatters hot , sharp case pieces ( " fragments " , " splinters " ) at high velocity . Most of the damage to soft targets such as unprotected personnel is caused by shell pieces rather than by the blast . The term " shrapnel " is sometimes used to describe the shell pieces , but shrapnel shell s functioned very differently and are long obsolete . Depending on the type of fuse used the HE shell can be set to burst on the ground ( percussion ) , in the air above the ground ( time or proximity ) , or after penetrating a short distance into the ground ( percussion with delay , either to transmit more ground shock to covered positions , or to reduce the spread of fragments ) . Early high explosives used before and during World War I in HE shells were Lyddite ( picric acid ) , PETN , TNT . However , pure TNT was expensive to produce and most nations made some use of mixtures using cruder TNT and ammonium nitrate , some with other compounds included . These fills included Ammonal , Schneiderite and Amatol . The latter was still in wide use in World War II . From 1944 to 1945 RDX and TNT mixtures became standard . Notably " Composition B " ( cyclotol ) . The introduction of ' insensitive munition ' requirements , agreements and regulations in the 1990s caused modern western designs to use various types of plastic bonded explosives ( PBX ) based on RDX . The percentage of shell weight taken up by its explosive fill increased steadily throughout the 20th Century . Less than 10 % was usual in the first few decades , by World War II leading designs were around 15 % . However , British researchers in that war identified 25 % as being the optimal design for anti - personnel purposes , based on recognition that far smaller fragments than hitherto would give the required effects . This was achieved by 1960s designed 155mm L15 shell developed as part of the FH - 70 program . The key requirement for increasing the HE content without increasing shell weight was to reduce the thickness of shell walls , this required improvements in high tensile steel . Mine shell . The mine shell is a particular form of HE shell developed for use in small caliber weapons such as 20 mm to 30 mm cannon . Small HE shells of conventional design can contain only a limited amount of explosive . By using a thin - walled steel casing of high tensile strength , a larger explosive charge can be used . Most commonly the explosive charge also was a more expensive but higher - detonation - energy type . The " mine shell " concept was invented by the Germans in the Second World War primarily for use in aircraft guns intended to be fired at opposing aircraft . Mine shells produced relatively little damage due to fragments , but a much more powerful blast . The aluminium structures and skins of Second World War aircraft were readily damaged by this greater level of blast . Armour - piercing . The earliest naval and anti - tank shells had to withstand the extreme shock of punching through armour plate . Shells designed for this purpose sometimes had a greatly strengthened case with a small bursting charge , and sometimes were solid metal , i . e . shot . In either case , they almost always had a specially hardened and shaped nose to facilitate penetration . This resulted in armour - piercing ( AP ) projectiles . A further refinement of such designs improved penetration by adding a softer metal cap to the penetrating nose giving armour - piercing , capped ( APC ) design . The softer cap dampen s the initial shock that would otherwise shatter the round . The best profile for the cap is not the most aerodynamic ; this can be remedied by adding a further hollow cap of suitable shape : APCBC ( APC + ballistic cap ) . AP shells with a bursting charge were sometimes distinguished by appending the suffix " HE " . At the beginning of the Second World War , solid shot AP projectiles were common . As the war progressed , ordnance design evolved so that APHE became the more common design approach for anti - tank shells of 75 mm caliber and larger , and more common in naval shell design as well . In modern ordnance , most full caliber AP shells are APHE designs . Armour - piercing , discarding - sabot . Armour - piercing , discarding - sabot ( APDS ) was developed by engineers working for the French Edgar Brandt company , and was fielded in two calibers ( 75 mm / 57 mm for the Mle1897 / 33 anti - tank cannon , 37 mm / 25 mm for several 37 mm gun types ) just before the French - German armistice of 1940 . The Edgar Brandt engineers , having been evacuated to the United Kingdom , joined ongoing APDS development efforts there , culminating in significant improvements to the concept and its realization . British APDS ordnance for their QF 6 pdr and 17 pdr anti - tank gun s was fielded in March 1944 . The armour - piercing concept calls for more penetration capability than the target ' s armour thickness . Generally , the penetration capability of an armor piercing round increases with the projectile ' s kinetic energy and also with concentration of that energy in a small area . Thus an efficient means of achieving increased penetrating power is increased velocity for the projectile . However , projectile impact against armour at higher velocity causes greater levels of shock . Materials have characteristic maximum levels of shock capacity , beyond which they may shatter , or otherwise disintegrate . At relatively high impact velocities , steel is no longer an adequate material for armor piercing rounds . Tungsten and tungsten alloys are suitable for use in even higher velocity armour piercing rounds , due to their very high shock tolerance and shatter resistance , and to their high melting and boiling temperatures . They also have very high density . Energy is concentrated by using a reduced - diameter tungsten shot , surrounded by a lightweight outer carrier , the " sabot " ( a French word for a wooden shoe ) . This combination allows the firing of a smaller diameter ( thus lower mass / aerodynamic resistance / penetration resistance ) projectile with a larger area of expanding - propellant " push " , thus a greater propelling force and resulting kinetic energy . Once outside the barrel , the sabot is stripped off by a combination of centrifugal force and aerodynamic force , giving the shot low drag in flight . For a given caliber the use of APDS ammunition can effectively double the anti - tank performance of a gun . Armour - piercing , fin - stabilized , discarding - sabot . An Armour - Piercing , Fin - Stabilised , Discarding Sabot ( APFSDS ) projectile uses the sabot principle with fin ( drag ) stabilisation . A long , thin sub - projectile has increased sectional density and thus penetration potential . However , once a projectile has a length - to - diameter ratio greater than 10 ( less for higher density projectiles ) , spin stabilisation becomes ineffective . Instead , drag stabilisation is used , by means of fins attached to the base of the sub - projectile , making it look like a large metal arrow . Large calibre APFSDS projectiles are usually fired from smooth - bore ( unrifled ) barrels , though they can be and often are fired from rifled guns . This is especially true when fired from small to medium calibre weapon systems . APFSDS projectiles are usually made from high - density metal alloys such as tungsten heavy alloys ( WHA ) or depleted uranium ( DU ) ; maraging steel was used for some early Soviet projectiles . DU alloys are cheaper and have better penetration than others as they are denser and self - sharpening . Uranium is also pyrophoric and may become opportunistic incendiaries especially as the round shears past the armor exposing non - oxidized metal , but both the metal ' s fragments and dust contaminate the battlefield with toxic hazards . The less toxic WHAs are preferred in most countries except the USA , UK , and Russia . Armour - piercing , composite rigid . Armour - piercing , composite rigid ( APCR ) is a British term , the US term for the design is high velocity armor piercing ( HVAP ) and German , " Hartkernmunition " . The APCR projectile is a core of a high - density hard material such as tungsten carbide surrounded by a full - bore shell of a lighter material ( e . g . , an aluminium alloy ) . Most APCR projectiles are shaped like the standard APCBC shot ( although some of the German Pzgr . 40 and some Soviet designs resemble a stubby arrow ) , but the projectile is lighter : up to half the weight of a standard AP shot of the same calibre . The lighter weight allows a higher velocity . The kinetic energy of the shot is concentrated in the core and hence on a smaller impact area , improving the penetration of the target armour . To prevent shattering on impact , a shock - buffering cap is placed between the core and the outer ballistic shell as with APC rounds . However , because the shot is lighter but still the same overall size it has poorer ballistic qualities , and loses velocity and accuracy at longer ranges . The APCR was superseded by the APDS which dispensed with the outer light alloy shell once the shot had left the barrel . The Germans used an APCR round , the " Panzergranate " 40 ( Pzgr . 40 ) " arrowhead " shot , for their 5 cm Pak 38 antitank guns in 1942 , and it was also developed for their 75 and 88 mm antitank and tank guns , and for anti - tank guns mounted in German aircraft . Shortages of the key component , tungsten , led to the Germans dropping the use of APCR during late World War II because tungsten was more efficiently used in industrial applications such as machine tools . The concept of a heavy , small - diameter penetrator encased in light metal would be later employed in small - arms armor - piercing incendiary and HEIAP rounds . Armour - piercing , composite non - rigid . Armour - piercing , composite non - rigid ( APCNR ) , the British term , but the more common terms are squeeze - bore and tapered bore and are based on the same projectile design as the APCR - a high density core within a shell of soft iron or other alloy , but it is fired by a gun with a tapered barrel , either a taper in a fixed barrel ( " Gerlich " design in German use ; original development efforts in the late 1930s in Germany , Denmark and France ) or a final added section as in the British Littlejohn adaptor . The projectile is initially full - bore , but the outer shell is deformed as it passes through the taper . Flanges or studs are swaged down in the tapered section , so that as it leaves the muzzle the projectile has a smaller overall cross - section . This gives it better flight characteristics with a higher sectional density and the projectile retains velocity better at longer ranges than an undeformed shell of the same weight . As with the APCR the kinetic energy of the round is concentrated at the core on impact . The initial velocity of the round is greatly increased by the decrease of barrel cross - sectional area toward the muzzle , resulting in a commensurate increase in velocity of the expanding propellant gases . The Germans deployed their initial design as a light anti - tank weapon , " 2 , 8 cm schwere Panzerbüchse 41 " , early in the Second World War , and followed on with the 4 . 2 cm Pak 41 and 7 . 5 cm Pak 41 . Although HE rounds were also put into service , they weighed only 93 grams and had low effectiveness . The British used the Littlejohn squeeze - bore adaptor which could be attached or removed as necessary . The adaptor extended the usefulness of armoured cars and light tanks which could not fit any gun larger than the QF 2 pdr . Although a full range of shells and shot could be used , changing the adaptor in the heat of battle was highly impractical . The APCNR was superseded by the APDS design which was compatible with non - tapered barrels . High - explosive , anti - tank . HEAT shells are a type of shaped charge used to defeat armoured vehicles . They are extremely efficient at defeating plain steel armour but less so against later composite and reactive armour . The effectiveness of the shell is independent of its velocity , and hence the range : it is as effective at 1000 metres as at 100 metres . The speed can even be zero in the case where a soldier simply places a magnetic mine onto a tank ' s armor plate . A HEAT charge is most effective when detonated at a certain , optimal , distance in front of the target and HEAT shells are usually distinguished by a long , thin nose probe sticking out in front of the rest of the shell and detonating it at the correct distance , e . g . , PIAT bomb . HEAT shells are less effective if spun ( i . e . , fired from a rifled gun ) . Discarding - sabot shell . A discarding - sabot shell ( DSS ) is ( in principle ) the same as the APDS shot but applied to high - explosive shells . It is a means to deliver a shell to a greater range . The design of the sub - projectile carried inside the sabot can be optimised for aerodynamic properties and the sabot can be built for best performance within the barrel of the gun . The principle was developed by a Frenchman , Edgar Brandt , in the 1930s . With the occupation of France , the Germans took the idea for application to anti - aircraft guns — a DSS projectile could be fired at a higher muzzle velocity and reach the target altitude more quickly , simplifying aiming and allowing the target aircraft less time to change course . High - explosive , squash - head or high - explosive plastic . High - explosive , squash - head ( HESH ) is another anti - tank shell based on the use of explosive . Developed by the British inventor Sir Charles Dennistoun Burney in World War II for use against fortifications . A thin - walled shell case contains a large charge of a plastic explosive . On impact the explosive flattens , without detonating , against the face of the armour , and is then detonated by a fuze in the base of the shell . Energy is transferred through the armour plate : when the compressive shock reflects off the air / metal interface on the inner face of the armour , it is transformed into a tension wave which spall s a " scab " of metal off into the tank damaging the equipment and crew without actually penetrating the armour . HESH is completely defeated by spaced armour , so long as the plates are individually able to withstand the explosion . It is still considered useful as not all vehicles are equipped with spaced armour , and it is also the most effective munition for demolishing brick and concrete . HESH shells , unlike HEAT shells , are best fired from rifled guns . Another variant is the high - explosive plastic ( HEP ) . Proof shot . A proof shot is not used in combat but to confirm that a new gun barrel can withstand operational stresses . The proof shot is heavier than a normal shot or shell , and an oversize propelling charge is used , subjecting the barrel to greater than normal stress . The proof shot is inert ( no explosive or functioning filling ) and is often a solid unit , although water , sand or iron powder filled versions may be used for testing the gun mounting . Although the proof shot resembles a functioning shell ( of whatever sort ) so that it behaves as a real shell in the barrel , it is not aerodynamic as its job is over once it has left the muzzle of the gun . Consequently it travels a much shorter distance and is usually stopped by an earth bank for safety measures . The gun , operated remotely for safety in case it fails , fires the proof shot , and is then inspected for damage . If the barrel passes the examination " proof mark s " are added to the barrel . The gun can be expected to handle normal ammunition , which subjects it to less stress than the proof shot , without being damaged . Shrapnel shells . Shrapnel shells were an early ( 1784 ) anti - personnel munition which delivered large numbers of bullet s at ranges far greater than rifles or machine guns could attain - up to 6 , 500 yards by 1914 . A typical shrapnel shell as used in World War I was streamlined , 75 mm ( 3 inch ) in diameter and contained approximately 300 lead - antimony balls ( bullets ) , each around 1 / 2 inch in diameter . Shrapnel used the principle that the bullets encountered much less air resistance if they travelled most of their journey packed together in a single streamlined shell than they would if they travelled individually , and could hence attain a far greater range . The gunner set the shell ' s time fuze so that it was timed to burst as it was angling down towards the ground just before it reached its target ( ideally about 150 yards before , and 60 – 100 feet above the ground ) . The fuze then ignited a small " bursting charge " in the base of the shell which fired the balls forward out of the front of the shell case , adding 200 – 250 ft / second to the existing velocity of 750 – 1200 ft / second . The shell body dropped to the ground mostly intact and the bullets continued in an expanding cone shape before striking the ground over an area approximately 250 yards × 30 yards in the case of the US 3 inch shell . The effect was of a large shotgun blast just in front of and above the target , and was deadly against troops in the open . A trained gun team could fire 20 such shells per minute , with a total of 6 , 000 balls , which compared very favourably with rifles and machine - guns . However , shrapnel ' s relatively flat trajectory ( it depended mainly on the shell ' s velocity for its lethality , and was only lethal in a forward direction ) meant that it could not strike trained troops who avoided open spaces and instead used dead ground ( dips ) , shelters , trenches , buildings , and trees for cover . It was of no use in destroying buildings or shelters . Hence it was replaced during World War I by the high - explosive shell which exploded its fragments in all directions and could be fired by high - angle weapons such as howitzers , hence far more difficult to avoid . Cluster shells . Cluster shells are a type of carrier shell or cargo munition . Like cluster bomb s , an artillery shell may be used to scatter smaller submunitions , including anti - personnel grenade s , anti - tank top - attack munitions , and landmines . These are generally far more lethal against both armor and infantry than simple high - explosive shells , since the multiple munitions create a larger kill zone and increase the chance of achieving the direct hit necessary to kill armor . Most modern armies make significant use of cluster munition s in their artillery batteries . However , in operational use submunitions have demonstrated a far higher malfunction rate than previously claimed , including those that have self - destruct mechanisms . This problem , the ' dirty battlefield " , led to the Ottawa Treaty . Artillery - scattered mines allow for the quick deployment of minefield s into the path of the enemy without placing engineering units at risk , but artillery delivery may lead to an irregular and unpredictable minefield with more unexploded ordnance than if mines were individually placed . Signatories of the Ottawa Treaty have renounced the use of cluster munitions of all types where the carrier contains more than ten submunitions . Chemical . Chemical shells contain just a small explosive charge to burst the shell , and a larger quantity of a chemical agent such as a poison gas . Signatories of the Chemical Weapons Convention have renounced such shells . Non - lethal shells . Not all shells are designed to kill or destroy . The following types are designed to achieve particular non - lethal effects . They are not completely harmless : smoke and illumination shells can accidentally start fires , and impact by the discarded carrier of all three types can wound or kill personnel , or cause minor damage to property . Smoke . The smoke shell is designed to create a smoke screen . The main types are bursting ( those filled with white phosphorus WP and a small HE bursting charge are best known ) and base ejection ( delivering three or four smoke canisters , or material impregnated with white phosphorus ) . Base ejection shells are a type of carrier shell or cargo munition . Base ejection smoke is usually white , however , coloured smoke has been used for marking purposes . The original canisters were non - burning , being filled with a compound that created smoke when it reacted with atmospheric moisture , modern ones use red phosphorus because of its multi - spectral properties . However , other compounds have been used , in World War II Germany used oleum ( fuming sulphuric acid ) and pumice . Illumination . Modern illuminating shells are a type of carrier shell or cargo munition . Those used in World War I were shrapnel pattern shells ejecting small burning ' pots ' . A modern illumination shell has a fuze which ejects the " candle " ( a pyrotechnic flare emitting white or infrared light ) at a calculated altitude , where it slowly drifts down beneath a heat resistant parachute , illuminating the area below . These are also known as " starshell " or " star shell " . Coloured flare shells have also been used for target marking purposes . Carrier . The carrier shell is simply a hollow carrier equipped with a fuze which ejects the contents at a calculated time . They are often filled with propaganda leaflets ( see external links ) , but can be filled with anything that meets the weight restrictions and is able to withstand the shock of firing . Famously , on Christmas Day 1899 during the siege of Ladysmith , the Boer s fired into Ladysmith a carrier shell without fuze , which contained a Christmas pudding , two Union Flags and the message " compliments of the season " . The shell is still kept in the museum at Ladysmith . Fireworks . Aerial firework bursts are created by shells . In the United States , consumer firework shells may not exceed 1 . 75 inches in diameter . Unexploded shells . The fuze of a shell has to keep the shell safe from accidental functioning during storage , due to ( possibly ) rough handling , fire , etc . , it also has to survive the violent launch through the barrel , then reliably function at the correct time . To do this it has a number of arming mechanisms , which are successively enabled under the influence of the firing sequence . Sometimes , one or more of these arming mechanisms fails , and if the fuze is installed on an HE shell , it fails to detonate on impact . More worrying and potentially far more hazardous are fully armed shells on which the fuze fails to initiate the HE firing . This may be due to shallow , low velocity or soft impact conditions . Whatever the reason for failure , such a shell is called a " blind " or " unexploded ordnance ( UXO ) " . The older term , " dud " , is discouraged because it implies that the shell " cannot " detonate . Blind shells often litter old battlefields and depending on the impact velocity may be buried some distance into the earth , all remain potentially hazardous . For example , antitank ammunition with a piezoelectric fuze can be detonated by relatively light impact to the piezoelectric element , and others , depending on the type of fuze used can be detonated by even a small movement . The battlefields of the First World War still claim casualties today from leftover munitions . Modern electrical and mechanical fuzes are highly reliable : if they do not arm correctly they keep the initiation train out of line , or if electrical in nature , discharge any stored electrical energy . Guided shells . Guided or " smart " ammunition have been developed in recent years , but have yet to supplant unguided munitions in all applications . Range enhancing technologies . Shells may be modified into Rocket Assisted Projectile s ( RAP ) and base bleed rounds to increase range .