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 vehicles (including tanks), and warships.

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 Bigyukjincheonroi in the reign of Seonjo of Joseon. (WP:CIRCULAR and WP:RSUE) 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 sabots.

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$1/2$ 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$1/2$ 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 shells and explosive shells inflicted terrible casualties on infantry, accounting for nearly 70% of all war casualties and leading to the adoption of steel helmets 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 guns, Gustav and Dora, which were 800 mm (31.5") in calibre. Very large shells have been replaced by rockets, 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 guns. 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 shells 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 dampens 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 guns 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 spalls 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 marks" 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 bullets 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 bombs, an artillery shell may be used to scatter smaller submunitions, including anti-personnel grenades, 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 munitions 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 minefields 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 Boers 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 Projectiles (RAP) and base bleed rounds to increase range.