The English word howitzer derives from the German word Haufen (heap) which as Gewalthaufen designated a pike square formation. Already in the Battle of Tannenberg (1410), the Teutonic Knights used artillery which was intended to break up enemy formations. During the Hussite Wars of the 1420s and 1430s, the Czechs used short barreled "houfnice cannons to fire at short distances into such crowds of Haufen infantry ("houf" came in use as the Czech word for crowd), or, to make horses skittish, into charging heavy cavalry. From the aufeniz mentioned in 1440 derive the German Haussnitz and later Haubitze, the Swedish haubits, Italian obice, and the Dutch word houwitser which led to the English word howitzer .
Since the First World War, the word "howitzer" has been increasingly used to describe artillery pieces that, strictly speaking, belong to the category of "gun-howitzer". This is particularly true in the armed forces of the United States, where gun-howitzers have been officially described as "howitzers" for more than sixty years. Because of this practice, the word "howitzer" is used in some armies as a generic term for any kind of artillery piece that is designed to strike targets on land. Thus, a number of artillery pieces that bear little resemblance to howitzers of earlier eras, such as the multi-chamber "supergun" designed by the Canadian artillery expert Gerald Bull for Iraq in the 1980s, are sometimes described as "howitzers".
The British had a further method of nomenclature that they adopted in the 19th century. Guns were categorised by projectile weight in pounds while howitzers were categorised by calibre in inches. This system broke down in the 1930s with the introduction of gun-howitzers.
The first modern howitzers were invented in Sweden towards the end of the seventeenth century. These were characterized by a shorter trail than other field guns meaning less stability when firing, which reduced the amount of powder that could be used; armies using these had to rely on a greater elevation angle to achieve a given range, which gave a steeper angle of descent.
Originally intended for use in siege warfare, they were particularly useful for delivering cast-iron shells filled with gunpowder or incendiary materials into the interior of fortifications. In contrast to contemporary mortars, which were fired at a fixed angle and were entirely dependent upon adjustments to the size of propellant charges in order to vary range, howitzers could be fired at a wide variety of angles. Thus, while howitzer gunnery was more complicated than the technique of employing mortars, the howitzer was an inherently more flexible weapon that could fire its projectiles along a wide variety of trajectories.
In the middle of the eighteenth century, a number of European armies began to introduce howitzers that were mobile enough to accompany armies in the field. Though usually fired at the relatively high angles of fire used by contemporary siege howitzers, these field howitzers were rarely defined by this capability. Rather, as the field guns of the day were usually restricted to inert projectiles (which relied entirely upon momentum to achieve their destructive effects), the field howitzers of the eighteenth century were chiefly valued for their ability to fire explosive shells. Thus, there were many cases which, for the sake of simplicity and rapidity of fire, dispensed with adjustable propellant charges.
In the mid-nineteenth century, some armies attempted to simplify their artillery parks by introducing smoothbore artillery pieces that were designed to fire both explosive projectiles and cannonballs, thereby replacing both field howitzers and field guns. The most famous of these "gun-howitzers" was the Napoleon 12-pounder, a weapon of French design that saw extensive service in the American Civil War.
In 1859, the armies of Europe (to include those which had recently adopted gun-howitzers) began to rearm their field batteries with rifled field guns. These new field pieces used cylindrical projectiles that, while smaller in calibre than the spherical shells of smoothbore field howitzers, could carry a comparable charge of gunpowder. Moreover, their greater range combined allowed them to create many of the same effects (such as firing over low walls) that had previously required the sharply curved trajectories of smoothbore field howitzers. Because of this, military authorities saw no point in obtaining rifled field howitzers to replace their smoothbore counterparts but, instead, used rifled field guns to replace both guns and howitzers.
In siege warfare, the introduction of rifling had the opposite effect. In the 1860s, artillery officers discovered that rifled siege howitzers (which were substantially larger than field howitzers) were a much more efficient means of destroying walls (and particularly walls that were protected by intervening obstacles of certain kinds) than either siege guns or siege mortars. Thus, at the same time that armies were taking howitzers of one sort out of their field batteries, they were introducing howitzers of another sort into their siege trains and fortresses. The lightest of these weapons (which would later become known as "light siege howitzers") had calibers in the vicinity of 150 mm or so and fired shells that weighed between 40 and 50 kilograms. The heaviest (which would later be called "medium siege howitzers") had calibers between 200 mm and 220 mm and fired shells that weighed about 100 kilograms(220 pounds).
During the 1880s, a third type of siege howitzer was added to inventories of a number of European armies. With calibers that ranged between 240 mm and 270 mm and shells that weighed more than 150 kilos, these soon came to be known as "heavy siege howitzers." A good example of a weapon of this class is provided by the 9.45-inch (240 mm) weapon that the British Army purchased from the Skoda works in 1899. (Intended for use against the fortifications of Pretoria, which fell before they could be used, and subsequently deployed to China for use against the fortifications of Peking, which also fell without a siege, the howitzer was never fired in anger.)
In the early 20th century, the introduction of howitzers that were significantly larger than the heavy siege howitzers of the day made necessary the creation of a fourth category, that of "super-heavy siege howitzers". Weapons of this category include the famous Big Bertha of the German Army and the 15-inch (381 mm) howitzer of the Royal Marine Artillery. These large howitzers were made possible by mechanical traction instead of horse teams. They were transported as several loads and had to be assembled on their firing position.
In the Russo-Turkish War of 1877-1878, the inability of rifled field guns to inflict significant damage upon field fortifications led to a revival of interest in field howitzers. By the 1890s, a number of European armies fielded either light (105 mm to 127 mm) or heavy (149 mm to 155 mm) field howitzers and a few, such as that of Germany, fielded both.
These field howitzers introduced at the end of the nineteenth century were valued for their ability to fire shells with high trajectories giving a steep angle of descent and, as a result, could strike targets that were protected by intervening obstacles. Howitzers of this era were also valued for their ability to fire shells that were about twice as large as shells fired by guns of the same size. Thus, while a 75 mm field gun that weighed one ton or so was limited to shells that weighed less than 8 kilograms, a 105 mm howitzer of the same weight could easily fire shells that weighed 15 or 16 kilograms. This is a matter of fundamental mechanics affecting the stability and hence the weight of the carriage. However, despite having a greater maximum elevation, the price was that howitzers had a shorter maximum range than the equivalent gun.
As heavy field howitzers and light siege howitzers of the late nineteenth and early twentieth centuries used ammunition of the same size and types, there was a marked tendency for the two types to merge. At first, this was largely a matter of the same basic weapon being employed on two different mountings. Later, as on-carriage recoil-absorbing systems eliminated many of the advantages that siege platforms had enjoyed over field carriages, the same combination of barrel assembly, recoil mechanism and carriage was used in both roles.
By the early 20th century the differences between guns and howitzers were relative not absolute and generally recognised as follows:
The onset of trench warfare after the first few months of First World War greatly increased the demand for howitzers that gave a steep angle of descent, which were better suited than guns to the task of striking targets on a horizontal plane (such as trenches) with large amounts of explosive and considerably less barrel wear. The army that reaped the greatest benefit from this phenomenon was that of Germany, which began the war with a far greater proportion of howitzers than the French.
Howitzers introduced in the course of World War I often had longer barrels than comparable weapons that had been introduced before 1914. Thus, while the standard German light field howitzer at the start of the war (the 10,5 cm leichte Feldhaubitze 98/09) had a barrel that was 16 calibers long, the light field howitzer adopted by the German Army in 1916 (105 mm leichte Feldhaubitze 16, see on the left) had a barrel that was 22 calibre long. At the same time, new models of field gun introduced during that conflict, such as the 77 mm field gun adopted by the German Army in 1916 (7,7 cm Feldkanone 16) were often provided with carriages that allowed firing at comparatively high angles and adjustable propellant cartridges. In other words, there was a marked tendency for howitzers to become more "gun-like" while guns were taking on some of the attributes of howitzers.
In the years after World War I, the tendency of guns and howitzers to acquire each others characteristics led to the renaissance of the concept of the gun-howitzer. This was a product of technical advances such as the French invention of autofrettage just before World War I, which led to stronger and lighter barrels, the use of cut-off gear to control recoil length depending on firing elevation angle, and the invention of muzzle brakes to reduce recoil forces. Like the gun-howitzers of the nineteenth century, those of the twentieth century replaced both guns and howitzers. Thus, the 25-pounder "gun-howitzer" of the British Army replaced both the 18-pounder field gun and the 4.5-inch howitzer. While this had the effect of simplifying such things as organization, training and the supply of ammunition, it created considerable confusion in the realm of nomenclature.
In the US Army, however, the preferred term was "howitzer". What is true for English, moreover, is also true for many other European languages. Thus, as gun-howitzers replaced both guns and howitzers, words such as "obusier" (French) and "Haubitze" (German), which had originally been used to designate weapons with relatively short barrels, were applied to weapons with much longer barrels.
Since World War II, most of the artillery pieces adopted by land armies for use as surface-to-surface use have combined the traditional characteristics of Guns and Howitzers - high muzzle velocity, long barrels, long range, multiple charges and maximum elevation angles greater than 45 degrees. The term 'Gun-Howitzer' is sometimes used for these (eg in Russia), many nations use Howitzer while UK calls them Guns.