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 contacted the target. Therefore, shells needed a time fuse that was ignited before or during firing and burned until the shell reached its target.
The 'flying-cloud thunderclap-eruptor' cannon from the Huolongjing
The earliest record of shells being used in combat was by the Republic of Venice at Jadra in 1376. Shells with fuses were used 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 Bowen (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. At least since the 16th Century grenades made of ceramics or glass were in use in Central Europe. A hoard of several hundred ceramic grenades were discovered during building works in front of a bastion of the Bavarian City of Ingolstadt, Germany dated to the 17th Century. Lots of the grenades contained their original blackpowder loads and igniters. Most probably the grenades were intentionally dumped in the moat of the bastion before the year 1723.
An early problem was that there was no means of precisely measuring the time to detonation — reliable fuses did not yet exist and 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. Nevertheless, shells came into regular use in the 16th Century, for example a 1543 English mortar shell was filled with 'wildfire'.
By the 18th Century, it was known that the fuse toward the muzzle could be lit by the flash through the windage between the shell and the barrel. At about this time, 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.
The use of exploding shells from field artillery became relatively commonplace from early in the 19th century. Until the mid 19th century, shells remained as simple exploding spheres that used gunpowder, set off by a slow burning fuse. They were usually made of cast iron, but bronze, lead, brass and even glass shell casings were experimented with. The word bomb 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. Typically, the thickness of the metal body was about a sixth of their diameter and they were about two thirds the weight of solid shot of the same calibre.
To ensure that shells were loaded with their fuses toward 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 a half inch. The sabot was also intended to reduce jamming during loading. Despite the use of exploding shell, the use of smoothbore cannons firing spherical projectiles of shot remained the dominant artillery method until the 1850s.
Original Shrapnel design
(left), and the Boxer design of May 1852 which avoided premature explosions (right)
By the late 18th century, artillery could use "canister shot" to defend itself from infantry or cavalry attack. This involved loading a tin or canvas container filled with small iron or lead balls instead of the usual cannonball. When fired, the container burst open during passage through the bore or at the muzzle, giving the effect of an oversized shotgun shell. At ranges of up to 300 m, canister shot was still highly lethal, though at this range the shots’ density was much lower, making a hit on a human target less likely. At longer ranges, solid shot or the common shell — a hollow cast iron sphere filled with black powder — was used, although with more of a concussive than a fragmentation effect, as the pieces of the shell were very large and sparse in number.
In 1784, Lieutenant Henry Shrapnel of the Royal Artillery developed the shrapnel shell as an anti-personnel weapon. His innovation was to combine the multi-projectile shotgun effect of canister shot, with a time fuze to open the canister and disperse the bullets it contained at some distance along the canister's trajectory from the gun. His shell was a hollow cast-iron sphere filled with a mixture of balls and powder, with a crude time fuse. If the fuse was set correctly, then the shell would break open, either in front or above the intended target, releasing its contents (of musket balls). The shrapnel balls would carry on with the "remaining velocity" of the shell.
1870s cast-iron RML
16-pounder "Boxer" shrapnel shell showing limited space for bullets
It took until 1803 for the British artillery to adopt the shrapnel shell (as "spherical case"), albeit with great enthusiasm when it did. Shrapnel was promoted to Major in the same year. The design was improved by Captain E. M. Boxer of the Royal Arsenal around 1852 and crossed over when cylindrical shells for rifled guns were introduced. Lieutenant-Colonel Boxer adapted his design in 1864 to produce shrapnel shells for the new rifled muzzle-loader (RML) guns : the walls were of thick cast iron, but the gunpowder charge was now in the shell base with a tube running through the centre of the shell to convey the ignition flash from the time fuze in the nose to the gunpowder charge in the base. The powder charge both shattered the cast iron shell wall and liberated the bullets.
In the 1870s, William Armstrong provided a design with the bursting charge in the head and the shell wall made of steel and hence much thinner than previous cast-iron shrapnel shell walls. While the thinner shell wall and absence of a central tube allowed the shell to carry far more bullets, it had the disadvantage that the bursting charge separated the bullets from the shell casing by firing the case forward and at the same time slowing the bullets down as they were ejected through the base of the shell casing, rather than increasing their velocity. Britain adopted this solution for several smaller calibres (below 6-inch); but, by World War I, few if any such shells remained.
The final shrapnel shell design used a much thinner forged steel shell case with a timer fuze in the nose and a tube running through the centre to convey the ignition flash to a gunpowder bursting charge in the shell base. The use of steel allowed the shell wall to be made much thinner and hence allow space for many more bullets. It also withstood the force of the powder charge without shattering, so that the bullets were fired forward out of the shell case with increased velocity, much like a shotgun. This is the design that came to be adopted by all countries and was in standard use when World War I began in 1914.
The mid 19th century saw a revolution in artillery, with the introduction of the first practical rifled breech loading weapons. The new methods resulted in the reshaping of the spherical shell into its modern recognizable cylindro-conoidal form. This shape greatly improved the in-flight stability of the projectile and meant that the primitive time fuzes could be replaced with the percussion fuze situated in the nose of the shell. The new shape also meant that further, armour-piercing designs could be used.
During the 20th Century, shells became increasingly streamlined. In World War I, ogives were typically two circular radius head (crh) - the curve was a segment of a circle having a radius of twice the shell calibre. After that war, ogive shapes became more complex and elongated. From the 1960s, higher quality steels were introduced by some countries for their HE shells, this enabled thinner shell walls with less weight of metal and hence a greater weight of explosive. Ogives were further elongated to improve their ballistic performance.
Rifled breech loaders
Advances in metallurgy in the industrial era allowed for the construction of rifled breech-loading guns that could fire at a much greater muzzle velocity. After the British artillery was shown up in the Crimean War as having barely changed since the Napoleonic Wars, the industrialist William Armstrong was awarded a contract by the government to design a new piece of artillery. Production started in 1855 at the Elswick Ordnance Company and the Royal Arsenal at Woolwich.
The piece was rifled, which allowed for a much more accurate and powerful action. Although rifling had been tried on small arms since the 15th century, the necessary machinery to accurately rifle artillery only became available in the mid-19th century. Martin von Wahrendorff and Joseph Whitworth independently produced rifled cannon in the 1840s, but it was Armstrong's gun that was first to see widespread use during the Crimean War. The cast iron shell of the Armstrong gun was similar in shape to a Minié ball and had a thin lead coating which made it fractionally larger than the gun's bore and which engaged with the gun's rifling grooves to impart spin to the shell. This spin, together with the elimination of windage as a result of the tight fit, enabled the gun to achieve greater range and accuracy than existing smooth-bore muzzle-loaders with a smaller powder charge.
The gun was also a breech-loader. Although attempts at breech-loading mechanisms had been made since medieval times, the essential engineering problem was that the mechanism couldn't withstand the explosive charge. It was only with the advances in metallurgy and precision engineering capabilities during the Industrial Revolution that Armstrong was able to construct a viable solution. Another innovative feature was what Armstrong called its "grip", which was essentially a squeeze bore; the 6 inches of the bore at the muzzle end was of slightly smaller diameter, which centered the shell before it left the barrel and at the same time slightly swaged down its lead coating, reducing its diameter and slightly improving its ballistic qualities.
Rifled guns were also developed elsewhere - by Major Giovanni Cavalli and Baron Martin von Wahrendorff in Sweden, 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 the Armstrong gun, 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 also 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 cupronickel or gilding metal were also used.
Although an early percussion fuze appeared in 1650 that used a flint to create sparks to ignite the powder, the shell had to fall in a particular way for this to work and this did not work with spherical projectiles. An additional problem was finding a suitably stable ‘percussion powder’. Progress was not possible until the discovery of mercury fulminate in 1800, leading to priming mixtures for small arms patented by the Rev Alexander Forsyth, and the copper percussion cap in 1818.
The percussion fuze was adopted by Britain in 1842. Many designs were jointly examined by the army and navy, but were unsatisfactory, probably because of the safety and arming features. However, in 1846 the design by Quartermaster Freeburn of the Royal Artillery was adopted by the army. It was a wooden fuze some 6 inches long and used shear wire to hold blocks between the fuze magazine and a burning match. The match was ignited by propellant flash and the shear wire broke on impact. A British naval percussion fuze made of metal did not appear until 1861.
Gunpowder was used as the only form of explosive up until the end of the 19th century. Guns using black powder ammunition would have their view obscured by a huge cloud of smoke and concealed shooters were given away by a cloud of smoke over the firing position. Guncotton, a nitrocellulose-based material, was discovered by Swiss chemist Christian Friedrich Schönbein in 1846. He promoted its use as a blasting explosive and sold manufacturing rights to the Austrian Empire. Guncotton was more powerful than gunpowder, but at the same time was somewhat more unstable. John Taylor obtained an English patent for guncotton; and John Hall & Sons began manufacture in Faversham. British interest waned after an explosion destroyed the Faversham factory in 1847. Austrian Baron Wilhelm Lenk von Wolfsberg built two guncotton plants producing artillery propellant, but it was dangerous under field conditions, and guns that could fire thousands of rounds using gunpowder would reach their service life after only a few hundred shots with the more powerful guncotton.
Small arms could not withstand the pressures generated by guncotton. After one of the Austrian factories blew up in 1862, Thomas Prentice & Company began manufacturing guncotton in Stowmarket in 1863; and British War Office chemist Sir Frederick Abel began thorough research at Waltham Abbey Royal Gunpowder Mills leading to a manufacturing process that eliminated the impurities in nitrocellulose making it safer to produce and a stable product safer to handle. Abel patented this process in 1865, when the second Austrian guncotton factory exploded. After the Stowmarket factory exploded in 1871, Waltham Abbey began production of guncotton for torpedo and mine warheads.
In 1884, Paul Vieille invented a smokeless powder called Poudre B (short for poudre blanche—white powder, as distinguished from black powder) made from 68.2% insoluble nitrocellulose, 29.8% soluble nitrocellusose gelatinized with ether and 2% paraffin. This was adopted for the Lebel rifle. Vieille's powder revolutionized the effectiveness of small guns, because it gave off almost no smoke and was three times more powerful than black powder. Higher muzzle velocity meant a flatter trajectory and less wind drift and bullet drop, making 1000 meter shots practicable. Other European countries swiftly followed and started using their own versions of Poudre B, the first being Germany and Austria which introduced new weapons in 1888. Subsequently, Poudre B was modified several times with various compounds being added and removed. Krupp began adding diphenylamine as a stabilizer in 1888.
Britain conducted trials on all the various types of propellant brought to their attention, but were dissatisfied with them all and sought something superior to all existing types. In 1889, Sir Frederick Abel, James Dewar and Dr W Kellner patented (Nos 5614 and 11,664 in the names of Abel and Dewar) a new formulation that was manufactured at the Royal Gunpowder Factory at Waltham Abbey. It entered British service in 1891 as Cordite Mark 1. Its main composition was 58% Nitro-glycerine, 37% Guncotton and 3% mineral jelly. A modified version, Cordite MD, entered service in 1901, this increased guncotton to 65% and reduced nitro-glycerine to 30%, this change reduced the combustion temperature and hence erosion and barrel wear. Cordite could be made to burn slower which reduced maximum pressure in the chamber (hence lighter breeches, etc.), but longer high pressure, significant improvements over gunpowder. Cordite could be made in any desired shape or size. The creation of cordite led to a lengthy court battle between Nobel, Maxim, and another inventor over alleged British patent infringement.
Although smokeless powders were used as a propellant, they could not be used as the substance for the explosive warhead, because shock sensitivity sometimes caused detonation in the artillery barrel at the time of firing. Picric acid was the first high-explosive nitrated organic compound widely considered suitable to withstand the shock of firing in conventional artillery. In 1885, based on research of Hermann Sprengel, French chemist Eugène Turpin patented the use of pressed and cast picric acid in blasting charges and artillery shells. In 1887, the French government adopted a mixture of picric acid and guncotton under the name Melinite. In 1888, Britain started manufacturing a very similar mixture in Lydd, Kent, under the name Lyddite.
Japan followed with an "improved" formula known as shimose powder. In 1889, a similar material, a mixture of ammonium cresylate with trinitrocresol, or an ammonium salt of trinitrocresol, started to be manufactured under the name ecrasite in Austria-Hungary. By 1894, Russia was manufacturing artillery shells filled with picric acid. Ammonium picrate (known as Dunnite or explosive D) was used by the United States beginning in 1906. Germany began filling artillery shells with TNT in 1902. Toluene was less readily available than phenol, and TNT is less powerful than picric acid, but the improved safety of munitions manufacturing and storage caused the replacement of picric acid by TNT for most military purposes between the World Wars. 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.
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 the recognition that far smaller fragments than hitherto would give a better effect. This guideline was achieved by the 1960s with the 155 mm L15 shell, developed as part of the German-British FH-70 program. The key requirement for increasing the HE content without increasing shell weight was to reduce the thickness of shell walls, which required improvements in high tensile steel.
With the introduction of the first ironclads in the 1850s and 1860s, it became clear that shells had to be designed to effectively pierce the ship armour. A series of British tests in 1863 demonstrated that the way forward lay with high-velocity lighter shells. The first pointed armour-piercing shell was introduced by Major Palliser in 1863. Approved in 1867, Palliser shot and shell was an improvement over the ordinary elongated shot of the time. Palliser shot was made of cast iron, the head being chilled in casting to harden it, using composite molds with a metal, water cooled portion for the head.
Britain also deployed Palliser shells in the 1870s-1880s. In the shell, the cavity was slightly larger than in the shot and was filled with gunpowder instead of being empty, to provide a small explosive effect after penetrating armour plating. The shell was correspondingly slightly longer than the shot to compensate for the lighter cavity. The powder filling was ignited by the shock of impact and hence did not require a fuze.
However, ship armour rapidly improved during the 1880s and 1890s, and it was realised that explosive shells with steel had advantages including better fragmentation and resistance to the stresses of firing. These were cast and forged steel.
An important development was the Armour-piercing discarding sabot, or APDS. An early version 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 75 mm 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.
The APDS projectile type was further developed in the United Kingdom between 1941-1944 by L. Permutter and S. W. Coppock, two designers with the Armaments Research Department. In mid-1944 the APDS projectile was first introduced into service for the UK’s QF 6 pdr anti-tank gun and later in September 1944 for the 17 pdr anti-tank gun. The idea was to use a stronger penetrator material to allow increased impact velocity and armour penetration.
A diagram of a fin stabilized discarding sabot showing its operation
The chosen new penetrator material, tungsten carbide, was too heavy at full bore to be accelerated to a sufficient muzzle velocity. To overcome this, a lightweight full diameter carrier shell (APCR) was developed to sheathe the inner high density core. However, the low sectional density of the APCR resulted in high aerodynamic drag. Instead, the British devised a way for the outer sheath to be discarded after leaving the bore. The name given to the discarded outer sheath was the sabot (a French word for a wooden shoe, also used to describe the standardized wood or paper-mache wadding around round shot in a smooth bore cannon).
Armour-piercing, composite non-rigid projectile design was a high density core within a shell of soft iron or other alloy, but fired by a gun with a tapered barrel. The projectile was initially full-bore, but the outer shell was deformed as it passes through the taper, leaving the projectile with a smaller overall cross-section and giving it better flight characteristics.
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 German taper was fixed on the barrel.
In contrast, 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.
Anti-tank explosive shells
Diagram of PIAT ammunition
High-explosive anti-tank warheads (HEAT for short) were developed during the Second World War as a munition made of an explosive shaped charge that uses the Munroe effect to create a very high-velocity partial stream of metal in a state of superplasticity, and used to penetrate solid vehicle armour.
Shaped charge warheads were promoted internationally by the Swiss inventor Henry Mohaupt, who exhibited the weapon before the Second World War. Prior to 1939 Mohaupt demonstrated his invention to British and French ordnance authorities.
Claims for priority of invention are difficult to resolve due to subsequent historic interpretations, secrecy, espionage, and international commercial interest. By mid-1940, Germany had introduced the first HEAT round to be fired by a gun, the 7.5 cm fired by the Kw.K.37 L/24 of the Panzer IV tank and the Stug III self-propelled gun (7.5 cm Gr.38 Hl/A, later editions B and C). In mid-1941, Germany started the production of HEAT rifle-grenades, first issued to paratroopers and by 1942 to the regular army units. In 1943, the Püppchen, Panzerschreck and Panzerfaust were introduced. The Panzerfaust and Panzerschreck or 'tank terror' gave the German infantryman the ability to destroy any tank on the battlefield from 50 – 150 m with relative ease of use and training (unlike the UK PIAT).
The first British HEAT weapon to be developed and issued was a rifle grenade using a 2 1/2 inch cup launcher on the end of the barrel; the British No. 68 AT grenade issued to the British army in 1940. By 1943, the PIAT was developed; a combination of a HEAT warhead and a spigot mortar delivery system. While cumbersome, the weapon at last allowed British infantry to engage armour at range; the earlier magnetic hand-mines and grenades required them to approach suicidally close. During World War II, the British referred to the Munroe effect as the cavity effect on explosives.
During the war, the French communicated Henry Mohaupt's technology to the U.S. Ordnance Department, who invited him to the USA, where he worked as a consultant on the Bazooka project.
HEAT rounds caused a revolution in anti-tank warfare when they were first introduced in the later stages of World War II. A single infantryman could effectively destroy any existing tank with a handheld weapon, thereby dramatically altering the nature of mobile operations. During World War II, weapons using HEAT warheads were known as having a hollow charge or shape charge warhead.
The high-explosive squash head (HESH) was developed by Charles Dennistoun Burney in the 1940s for the British war effort, originally as an anti-fortification "wallbuster" munition for use against concrete. HESH rounds were thin metal shells filled with plastic explosive and a delayed-action base fuze. The plastic explosive is "squashed" against the surface of the target on impact and spreads out to form a disc or "pat" of explosive. The base fuze detonates the explosive milliseconds later, creating a shock wave that, owing to its large surface area and direct contact with the target, is transmitted through the material. At the point where the compression and tension waves intersect a high-stress zone is created in the metal, causing pieces of steel to be projected off the interior wall at high velocity. This fragmentation by blast wave is known as spalling, with the fragments themselves known as spall. Unlike high-explosive anti-tank (HEAT) rounds, which are shaped charge ammunition, HESH shells are not specifically designed to perforate the armour of main battle tanks. HESH shells rely instead on the transmission of the shock wave through the solid steel armour.
HESH was found to be surprisingly effective against metallic armour as well, although the British already had effective weapons using HEAT, such as the PIAT. HESH was for some time a competitor to the more common HEAT round, again in combination with recoilless rifles as infantry weapons and was effective against tanks such as the T-55 and T-62.
Other shell types
A variety of fillings have been used in shells throughout history. An incendiary shell was invented by Valturio in 1460. The carcass shell was first used by the French under Louis XIV in 1672. Initially in the shape of an oblong in an iron frame (with poor ballistic properties) it evolved into a spherical shell. Their use continued well into the 19th century.
A modern version of the incendiary shell was developed in 1857 by the British and was known as Martin's shell after its inventor. The shell was filled with molten iron and was intended to break up on impact with an enemy ship, splashing molten iron on the target. It was used by the Royal Navy between 1860 and 1869, replacing Heated shot as an anti-ship, incendiary projectile.
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 51⁄2 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 19th century British service, they were made of concentric paper with a thickness about 1/15th of the 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.