Mortar ( weapon ) A mortar is an indirect fire weapon that fires explosive projectiles known as ( mortar ) bombs at low velocities , short ranges and high - arcing ballistic trajectories . It is typically muzzle - loading and has a barrel length less than 15 times its caliber . Function . A mortar is relatively simple and easy to operate . A modern mortar consists of a tube into which assistant gunners drop a purpose - designed bomb . The tube is generally set at between 45 and 85 degrees angle to the ground , with the higher angle giving shorter firing distances . The bomb has a small baseline charge and no cartridge case ; for extra range propellant rings are attached to the bomb ' s fins . When it reaches the base of the tube it hits a fixed firing pin , which detonates the baseline charge and fires the projectile . Some mortars have a moving firing pin , operated by a lanyard ; others may be fired by a trigger . These attributes contrast with the mortar ' s larger siblings , howitzer s and field gun s , that fire shells at higher velocities , longer ranges , flatter arcs , sometimes using direct fire . These weapons are also breech - loaded , while most mortars are muzzle - loaded . From the 18th to the early 20th century very heavy , relatively immobile siege mortars were used , of up to one metre calibre , often made of cast iron and with outside barrel diameter many times that of the bore diameter . Smaller and more portable designs were introduced during the First World War , primarily for trench warfare , which took place at relatively close ranges . Mortars continue to be in use to the present day . Light and medium mortars are portable , and usually used by infantry units . The chief advantage a mortar section has over an artillery battery is the flexibility of small numbers , mobility and the ability to engage targets in cover with plunging fire . Mortars are able to fire from the protection of a trench or other type of cover . In these aspects , the mortar is an excellent infantry support weapon , as it can be transported over any terrain and is not burdened by the logistical support needed for artillery . Heavy mortars are typically between 120 - and 300 - mm calibre . These weapons are usually towed or vehicle - mounted , sometimes breech - loaded , and normally employed by infantry units attached to battalion through division level . Even at this size , mortars are simpler and less expensive than comparable howitzers or field guns . A mortar can be carried by one or more people ( larger mortars can usually be broken down into components ) , or transported in a vehicle . An infantry mortar can usually also be mounted and fired from a mortar - carrier , a purpose - built or modified armoured vehicle with a large roof - hatch . A mortar can also be a launcher for fireworks , a hand - held or vehicle - mounted projector for smoke shells or flares , or a large grenade launcher . Heavy mortars can be mounted on a towed carriage , or permanently vehicle - mounted as a self - propelled mortar . Twin - barrelled self - loading mortars — such as the Patria AMOS PT1 — are the latest evolution of these heavy mortars and are mounted on platforms such as armoured personnel carriers , tank chassis , and coastal patrol boats . Design . Most modern mortar systems consist of three main components : a barrel , a base plate , and a bipod . Modern mortars normally range in calibre from 60 mm ( 2 . 36 in ) to 120 mm ( 4 . 72 in ) . However , mortars both larger and smaller than these specifications have been produced . An example of the smaller scale is the British 51 mm Light Mortar which is carried by an individual and consists of only a tube and a base plate . Conversely , a large example is the Soviet 2S4 M1975 " Tyulpan " ( tulip flower ) 240 mm self - propelled mortar . Smaller mortars ( up to 82 mm ) are commonly used and transported by infantry based mortar sections as a substitute for , or in addition to , artillery . Ammunition for mortars generally comes in two main varieties : fin - stabilised and spin - stabilised . The former have short fins on their posterior portion which control the path of the bomb in flight . Spin - stabilized mortar bombs rotate as they travel along and leave the mortar tube , which stabilizes them in much the same way as a rifle bullet . Both types of rounds can be either illumination ( infra - red or visible illumination ) , smoke , or high explosive . Spin - stabilised rounds may be fired from a smoothbore or a rifled barrel . Since mortars are generally muzzle loaded , mortar bombs for rifled barrels have a pre - engraved band , called an obturator , that engages with the rifling of the barrel . They are more accurate , but slower to load . Mortars are made in a range of calibres . The French 81 mm mortar became standard for many countries , while the Soviet bloc standardized on the 82mm mortar . Mortars suffer from instability when used on snow and soft ground , because the recoil pushes them into the ground or snow unevenly . A solution to this problem is the Raschen Bag . Distinctive features of mortars . Mortars and their ammunition are generally much smaller and lighter than other artillery , such as guns and howitzers , which allows light and medium ( typically , 60mm and 81 / 82mm ) mortars to be considered small - arms ; i . e . capable of transport by personnel without vehicle assistance . They are short - range weapons , and often more effective than other artillery for many purposes within their shorter range . In particular , due its high , parabolic trajectory with a near vertical descent , the mortar can land bombs on nearby targets , including those behind obstacles or in fortifications , such as light vehicles behind hills or structures , or infantry in trenches or spider holes . This also makes it possible to launch attacks from positions lower than the target of the attack . ( E . g . , long - range artillery could not shell a target 1 km away and 30 metres ( 100 ft ) higher ; a target easily accessible to a mortar . Mortars are also highly effective when used from concealed positions , such as the natural escarpments on hillsides or from woods , especially if forward observers are being employed in strategic positions to direct fire ; an arrangement where the mortar is in relatively close proximity both to its FO and its target , allowing for fire to be quickly and accurately delivered to lethal effect . Fin - stabilised mortar bombs do not have to withstand the rotational forces placed upon them by rifling or greater pressures , and can therefore carry a higher payload in a thinner skin than rifled artillery ammunition . Due to the difference in available volume , a smooth - bore mortar of a given diameter will have a greater explosive yield than a similarly sized artillery shell . For example , a 120 mm mortar bomb has about the same explosive capability as a 155 mm artillery shell . Also , fin - stabilised munitions fired from a smooth - bore , which do not rely upon the spin imparted by a rifled - bore for greater accuracy , do not have the drawback of veering in the direction of the spin . Spigot mortar . Spigot mortars , a particular type of mortar , consist of a mostly solid rod or spigot , onto which a hollow tube in the projectile fits - inverting the normal tube - mortar arrangement . At the top of the tube in the projectile , a cavity contains propellant such as cordite . There is usually a trigger mechanism built into the base of the spigot , with a long firing pin running up the length of the spigot activating a primer inside the projectile and firing the propellant charge . The advantage of a spigot mortar is that the firing unit ( baseplate and spigot ) is smaller and lighter than a conventional tube mortar of equivalent payload and range . It is also somewhat simpler to manufacture . The disadvantage is that while most mortar bombs have a streamlined shape towards the back that fits a spigot mortar application well , using that space for the spigot mortar tube takes volume and mass away from the payload of the projectile . If a soldier is carrying only a few projectiles , the projectile weight disadvantage is not significant . However , the weight of a large quantity of the heavier and more complex spigot projectiles offsets the weight saved due to the spigot mortar being lighter than a conventional mortar . A near - silent mortar can operate using the spigot principle . Each round has a close - fitting movable plug in the tube that fits over the spigot . When the round is fired , the projectile is pushed off the spigot , but before the plug clears the spigot it is caught by a constriction at the base of the tube . This traps the gases from the propelling charge and hence the sound of the firing . After World War II the Belgium Fly - K silent spigot mortar was accepted into French service as the TN - 8111 . Spigot mortars are generally out of favor in modern usage , replaced by small conventional mortars . Military applications of spigot mortars include Non - military applications include the use of small - calibre spigot mortars to launch lightweight , low - velocity foam dummy targets used for training retriever dogs for bird hunting . Extremely simple launchers use a separate small primer cap as the sole propellant ( similar or identical to the cartridges used in industrial nail gun s ) . History . Mortars have existed for hundreds of years , first seeing use in siege warfare . Many historians claim that the first mortars were used at the 1453 siege of Constantinople by Fatih Sultan Mehmed . A European account of the 1456 siege of Belgrade by Giovanni da Tagliacozzo credits the Ottoman Turks for using seven mortars that fired " stone shots one Italian mile high " . The speed of these was apparently slow enough that casualties could be avoided by posting observers that gave warning of their trajectories . Early mortars , such as the Pumhart von Steyr , were also large and heavy , and could not be easily transported . Simply made , these weapons were no more than iron bowls reminiscent of the kitchen and apothecary mortar s from where they drew their name . An early transportable mortar was invented by Baron Menno van Coehoorn ( Siege of Grave , 1673 ) . An early use of these more mobile mortars as field ( rather than siege ) weapons was by the Government forces which suppressed the 1719 Jacobite rising at the Battle of Glen Shiel ; they would have had great advantages over field guns in the almost roadless West Highlands of Scotland . Coehorn - type mortars of approximately weight were used by both sides during the American Civil War . At the Siege of Vicksburg , General US Grant reported making such mortars " by taking logs of the toughest wood that could be found , boring them out for six or twelve - pound shells and binding them with stong iron bands . These answered as coehorn s , and shells were successfully thrown from them into the trenches of the enemy . " During the Russo - Japanese War , Leonid Gobyato for the first time applied deflection from closed firing positions in the field and with General Roman Kondratenko designed the first mortar that fired navy shells . However , it was not until the Stokes trench mortar devised by Sir Wilfred Stokes in 1915 , that the modern mortar transportable by one person was born . The Germans also developed a series of trench mortars or Minenwerfer in calibers from 7 . 58 cm to 25 cm during World War I , though these were rifled . Extremely useful in the muddy trenches of the Western Front , mortars were praised because of the bombs ' high angle of flight ; a mortar round could be aimed to fall directly into trench es where artillery shells , due to their low angle of flight , could not possibly go . Modern mortars have improved upon these designs , offering a weapon that is light , adaptable , easy to operate , and yet possesses enough accuracy and firepower to provide the infantry with quality close fire support against soft and hard targets more quickly than any other means . During the battle of Iwo Jima , the Imperial Japanese Army used twelve 320 mm mortar s against the American forces . Largest mortars . The largest mortars ever developed were the French " Monster Mortar " ( 36 French inches ; 975 mm ; developed by Henri - Joseph Paixhans in 1832 ) , Mallet ' s Mortar ( 36 inches ; 910 mm ; designed by Robert Mallet and tested by the Woolwich Arsenal , London , in 1857 ) and the " Little David " ( 36 inches ; 914 . 4 mm ; developed in the United States for use in World War II ) . All three mortars had a caliber of 36 " inches " , but only the " Monster Mortar " saw action ( at the Battle of Antwerp in 1832 ) . Improvised mortars . Improvised , or " home - made " , mortars have been used by insurgent groups , usually to attack fortified military installations or to terrorize civilians . The Provisional Irish Republican Army used some of the best - known examples during the 1970s , 1980s and 1990s . The largest types came to be known as " barracks busters " and were usually constructed from heavy steel piping mounted on a steel frame . The largest had a calibre of and fired home - made rounds carrying from of explosive . As each tube fired only one round , mortars were usually deployed as a battery of four or six welded onto a steel frame . This was often concealed inside a van such as a Ford Transit . The vehicle would be parked , pointing roughly at the target . A timer fired the propellant charges after a delay – this allowed the mortar gunner time to escape . After firing , a timer - operated incendiary device could set the vehicle on fire in order to destroy any forensic evidence it contained . Well - known incidents using these weapons include the 1985 Newry mortar attack , when nine members of the Royal Ulster Constabulary were killed , and the Downing Street mortar attack in 1991 . The IRA mortared 10 Downing Street as a Cabinet meeting was in session . Three bombs were launched but only one detonated , it landed in the back garden of the British Prime Minister ' s residence and only shattered the rear windows . Prime Minister John Major had to move to Admiralty House while repairs were effected .