In physics, a shock wave, or shock, is a type of propagating disturbance that moves faster than the local speed of sound in the medium. Like an ordinary wave, a shock wave carries energy and can propagate through a medium but is characterized by an abrupt, nearly discontinuous, change in pressure and density of the medium. For the purpose of comparison, in supersonic flows, additional increased expansion may be achieved through an expansion fan known as a Prandtl–Meyer expansion fan; the accompanying expansion wave may approach and collide and recombine with the shock wave, creating a process of destructive interference. The sonic boom associated with the passage of a supersonic aircraft is a type of sound wave produced by constructive interference. Unlike solitons, the energy and speed of a shock wave alone dissipates quickly with distance; when a shock wave passes through matter, energy is preserved but entropy increases. This change in the matter's properties manifests itself as a decrease in the energy which can be extracted as work, as a drag force on supersonic objects.
Shock waves can be: Normal At 90° to the shock medium's flow direction. Oblique At an angle to the direction of flow. Bow Occurs upstream of the front of a blunt object when the upstream flow velocity exceeds Mach 1; some other terms Shock front: The boundary over which the physical conditions undergo an abrupt change because of a shock wave. Contact front: In a shock wave caused by a driver gas, the boundary between the driver and the driven gases; the Contact Front trails the Shock Front. The abruptness of change in the features of the medium, that characterize shock waves, can be viewed as a phase transition: the pressure-time diagram of a supersonic object propagating shows how the transition induced by a shock wave is analogous to a dynamic phase transition; when an object moves faster than the information can propagate into the surrounding fluid the fluid near the disturbance cannot react or "get out of the way" before the disturbance arrives. In a shock wave the properties of the fluid change instantaneously.
Measurements of the thickness of shock waves in air have resulted in values around 200 nm, on the same order of magnitude as the mean free gas molecule path. In reference to the continuum, this implies the shock wave can be treated as either a line or a plane if the flow field is two-dimensional or three-dimensional, respectively. Shock waves are formed when a pressure front moves at supersonic speeds and pushes on the surrounding air. At the region where this occurs, sound waves travelling against the flow reach a point where they cannot travel any further upstream and the pressure progressively builds in that region. Shock waves are not conventional sound waves. Shock waves in air are heard as "snap" noise. Over longer distances, a shock wave can change from a nonlinear wave into a linear wave, degenerating into a conventional sound wave as it heats the air and loses energy; the sound wave is heard as the familiar "thud" or "thump" of a sonic boom created by the supersonic flight of aircraft.
The shock wave is one of several different ways in which a gas in a supersonic flow can be compressed. Some other methods are isentropic compressions, including Prandtl–Meyer compressions; the method of compression of a gas results in different temperatures and densities for a given pressure ratio which can be analytically calculated for a non-reacting gas. A shock wave compression results in a loss of total pressure, meaning that it is a less efficient method of compressing gases for some purposes, for instance in the intake of a scramjet; the appearance of pressure-drag on supersonic aircraft is due to the effect of shock compression on the flow. In elementary fluid mechanics utilizing ideal gases, a shock wave is treated as a discontinuity where entropy increases over a nearly infinitesimal region. Since no fluid flow is discontinuous, a control volume is established around the shock wave, with the control surfaces that bound this volume parallel to the shock wave; the two surfaces are separated by a small depth such that the shock itself is contained between them.
At such control surfaces, mass flux and energy are constant. It is assumed the system is adiabatic and no work is being done; the Rankine–Hugoniot conditions arise from these considerations. Taking into account the established assumptions, in a system where the downstream properties are becoming subsonic: the upstream and downstream flow properties of the fluid are considered isentropic. Since the total amount of energy within the system is constant, the stagnation enthalpy remains constant over both regions. Though, entropy is increasing; when analyzing shock waves in a flow field, which are still attached to the body, the shock wave, deviating at some arbitrary angle from the flow direction is termed oblique shock. These shocks require a component vector analysis of the flow.
The British Army is the principal land warfare force of the United Kingdom, a part of British Armed Forces. As of 2018, the British Army comprises just over 81,500 trained regular personnel and just over 27,000 trained reserve personnel; the modern British Army traces back to 1707, with an antecedent in the English Army, created during the Restoration in 1660. The term British Army was adopted in 1707 after the Acts of Union between Scotland. Although all members of the British Army are expected to swear allegiance to Elizabeth II as their commander-in-chief, the Bill of Rights of 1689 requires parliamentary consent for the Crown to maintain a peacetime standing army. Therefore, Parliament approves the army by passing an Armed Forces Act at least once every five years; the army is commanded by the Chief of the General Staff. The British Army has seen action in major wars between the world's great powers, including the Seven Years' War, the Napoleonic Wars, the Crimean War and the First and Second World Wars.
Britain's victories in these decisive wars allowed it to influence world events and establish itself as one of the world's leading military and economic powers. Since the end of the Cold War, the British Army has been deployed to a number of conflict zones as part of an expeditionary force, a coalition force or part of a United Nations peacekeeping operation; until the English Civil War, England never had a standing army with professional officers and careerist corporals and sergeants. It relied on militia organized by local officials, or private forces mobilized by the nobility, or on hired mercenaries from Europe. From the Middle Ages until the English Civil War, when a foreign expeditionary force was needed, such as the one that Henry V of England took to France and that fought at the Battle of Agincourt, the army, a professional one, was raised for the duration of the expedition. During the English Civil War, the members of the Long Parliament realised that the use of county militia organised into regional associations commanded by local members of parliament, while more than able to hold their own in the regions which Parliamentarians controlled, were unlikely to win the war.
So Parliament initiated two actions. The Self-denying Ordinance, with the notable exception of Oliver Cromwell, forbade members of parliament from serving as officers in the Parliamentary armies; this created a distinction between the civilians in Parliament, who tended to be Presbyterian and conciliatory to the Royalists in nature, a corps of professional officers, who tended to Independent politics, to whom they reported. The second action was legislation for the creation of a Parliamentary-funded army, commanded by Lord General Thomas Fairfax, which became known as the New Model Army. While this proved to be a war winning formula, the New Model Army, being organized and politically active, went on to dominate the politics of the Interregnum and by 1660 was disliked; the New Model Army was paid off and disbanded at the Restoration of the monarchy in 1660. For many decades the excesses of the New Model Army under the Protectorate of Oliver Cromwell was a horror story and the Whig element recoiled from allowing a standing army.
The militia acts of 1661 and 1662 prevented local authorities from calling up militia and oppressing their own local opponents. Calling up the militia was possible only if the king and local elites agreed to do so. Charles II and his Cavalier supporters favoured a new army under royal control; the first English Army regiments, including elements of the disbanded New Model Army, were formed between November 1660 and January 1661 and became a standing military force for Britain. The Royal Scots and Irish Armies were financed by the parliaments of Ireland. Parliamentary control was established by the Bill of Rights 1689 and Claim of Right Act 1689, although the monarch continued to influence aspects of army administration until at least the end of the nineteenth century. After the Restoration Charles II pulled together four regiments of infantry and cavalry, calling them his guards, at a cost of £122,000 from his general budget; this became the foundation of the permanent English Army. By 1685 it had grown to 7,500 soldiers in marching regiments, 1,400 men permanently stationed in garrisons.
A rebellion in 1685 allowed James II to raise the forces to 20,000 men. There were 37,000 in 1678. After William and Mary's accession to the throne England involved itself in the War of the Grand Alliance to prevent a French invasion restoring James II. In 1689, William III expanded the army to 74,000, to 94,000 in 1694. Parliament was nervous, reduced the cadre to 7000 in 1697. Scotland and Ireland had theoretically separate military establishments, but they were unofficially merged with the English force. By the time of the 1707 Acts of Union, many regiments of the English and Scottish armies were combined under one operational command and stationed in the Netherlands for the War of the Spanish Succession. Although all the regiments were now part of the new British military establishment, they remained under the old operational-command structure and retained much of the institutional ethos and traditions of the standing armies created shortly after the restoration of the monarchy 47 years earlier.
The order of seniority of the most-senior British Army line regiments is based on that of the English army
United States Armed Forces
The United States Armed Forces are the military forces of the United States of America. It consists of the Army, Marine Corps, Air Force, Coast Guard; the President of the United States is the Commander-in-Chief of the Armed Forces and forms military policy with the Department of Defense and Department of Homeland Security, both federal executive departments, acting as the principal organs by which military policy is carried out. All five armed services are among the seven uniformed services of the United States. From the time of its inception, the U. S. Armed Forces played a decisive role in the history of the United States. A sense of national unity and identity was forged as a result of victory in the First Barbary War and the Second Barbary War. So, the founders of the United States were suspicious of a permanent military force, it played a critical role in the American Civil War, continuing to serve as the armed forces of the United States, although a number of its officers resigned to join the military of the Confederate States.
The National Security Act of 1947, adopted following World War II and during the Cold War's onset, created the modern U. S. military framework. The Act established the National Military Establishment, headed by the Secretary of Defense, it was amended in 1949, renaming the National Military Establishment the Department of Defense, merged the cabinet-level Department of the Army, Department of the Navy, Department of the Air Force, into the Department of Defense. The U. S. Armed Forces are one of the largest militaries in terms of the number of personnel, it draws its personnel from a large pool of paid volunteers. Although conscription has been used in the past in various times of both war and peace, it has not been used since 1973, but the Selective Service System retains the power to conscript males, requires that all male citizens and residents residing in the U. S. between the ages of 18–25 register with the service. On February 22, 2019, however, a federal judge ruled that registering only males for Selective Service is unconstitutional.
As of 2017, the U. S. spends about US$610 billion annually to fund its military forces and Overseas Contingency Operations. Put together, the U. S. constitutes 40 percent of the world's military expenditures. The U. S. Armed Forces has significant capabilities in both defense and power projection due to its large budget, resulting in advanced and powerful technologies which enables a widespread deployment of the force around the world, including around 800 military bases outside the United States; the U. S. Air Force is the world's largest air force, the U. S. Navy is the world's largest navy by tonnage, the U. S. Navy and the U. S. Marine Corps combined are the world's second largest air arm. In terms of size, the U. S. Coast Guard is the world's 12th largest naval force; the history of the U. S. Armed Forces dates to 14 June 1775, with the creation of the Continental Army before the Declaration of Independence marked the establishment of the United States; the Continental Navy, established on 13 October 1775, Continental Marines, established on 10 November 1775, were created in close succession by the Second Continental Congress in order to defend the new nation against the British Empire in the American Revolutionary War.
These forces demobilized in 1784. The Congress of the Confederation created the current United States Army on 3 June 1784; the United States Congress created the current United States Navy on 27 March 1794 and the current United States Marine Corps on 11 July 1798. All three services trace their origins to their respective Continental predecessors; the 1787 adoption of the Constitution gave the Congress the power to "raise and support armies", to "provide and maintain a navy" and to "make rules for the government and regulation of the land and naval forces", as well as the power to declare war. The President is the U. S. Armed Forces' commander-in-chief; the United States Coast Guard traces its origin to the founding of the Revenue Cutter Service on 4 August 1790 which merged with the United States Life-Saving Service on 28 January 1915 to establish the Coast Guard. The United States Air Force was established as an independent service on 18 September 1947. S. Signal Corps, formed 1 August 1907 and was part of the Army Air Forces before becoming an independent service as per the National Security Act of 1947.
The United States Public Health Service Commissioned Corps was considered to be a branch of the United States Armed Forces from 29 July 1945 until its status as such was revoked on 3 July 1952. On March 1st, 2019, the Department of Defense sent a proposal to Congress that would establish the United States Space Force as an independent military service within the Department of the Air Force. If approved, this would become the sixth military service branch to be created. Command over the U. S. Armed Forces is established in the Constitution; the sole power of command is vested in the President by Article II as Commander-in-Chief. The Constitution presumes the existence of "executive Departments" headed by "principal officers", whose appointment mechanism is provided for in the Appointments Clause; this allowance in the Constitution formed the basis for creation of the Department of Defense in 1947 by the National Security Act. The DoD is headed by the Secretary of Defense, a civilian and member of the Cabinet.
The Defense Secretary is second in the U. S. Armed Forces chain of command, with the exception of the Coast Guard, under the Secretary of Homeland Security, is just below the President and serves as the
World War II
World War II known as the Second World War, was a global war that lasted from 1939 to 1945. The vast majority of the world's countries—including all the great powers—eventually formed two opposing military alliances: the Allies and the Axis. A state of total war emerged, directly involving more than 100 million people from over 30 countries; the major participants threw their entire economic and scientific capabilities behind the war effort, blurring the distinction between civilian and military resources. World War II was the deadliest conflict in human history, marked by 50 to 85 million fatalities, most of whom were civilians in the Soviet Union and China, it included massacres, the genocide of the Holocaust, strategic bombing, premeditated death from starvation and disease, the only use of nuclear weapons in war. Japan, which aimed to dominate Asia and the Pacific, was at war with China by 1937, though neither side had declared war on the other. World War II is said to have begun on 1 September 1939, with the invasion of Poland by Germany and subsequent declarations of war on Germany by France and the United Kingdom.
From late 1939 to early 1941, in a series of campaigns and treaties, Germany conquered or controlled much of continental Europe, formed the Axis alliance with Italy and Japan. Under the Molotov–Ribbentrop Pact of August 1939, Germany and the Soviet Union partitioned and annexed territories of their European neighbours, Finland and the Baltic states. Following the onset of campaigns in North Africa and East Africa, the fall of France in mid 1940, the war continued between the European Axis powers and the British Empire. War in the Balkans, the aerial Battle of Britain, the Blitz, the long Battle of the Atlantic followed. On 22 June 1941, the European Axis powers launched an invasion of the Soviet Union, opening the largest land theatre of war in history; this Eastern Front trapped most crucially the German Wehrmacht, into a war of attrition. In December 1941, Japan launched a surprise attack on the United States as well as European colonies in the Pacific. Following an immediate U. S. declaration of war against Japan, supported by one from Great Britain, the European Axis powers declared war on the U.
S. in solidarity with their Japanese ally. Rapid Japanese conquests over much of the Western Pacific ensued, perceived by many in Asia as liberation from Western dominance and resulting in the support of several armies from defeated territories; the Axis advance in the Pacific halted in 1942. Key setbacks in 1943, which included a series of German defeats on the Eastern Front, the Allied invasions of Sicily and Italy, Allied victories in the Pacific, cost the Axis its initiative and forced it into strategic retreat on all fronts. In 1944, the Western Allies invaded German-occupied France, while the Soviet Union regained its territorial losses and turned toward Germany and its allies. During 1944 and 1945 the Japanese suffered major reverses in mainland Asia in Central China, South China and Burma, while the Allies crippled the Japanese Navy and captured key Western Pacific islands; the war in Europe concluded with an invasion of Germany by the Western Allies and the Soviet Union, culminating in the capture of Berlin by Soviet troops, the suicide of Adolf Hitler and the German unconditional surrender on 8 May 1945.
Following the Potsdam Declaration by the Allies on 26 July 1945 and the refusal of Japan to surrender under its terms, the United States dropped atomic bombs on the Japanese cities of Hiroshima and Nagasaki on 6 and 9 August respectively. With an invasion of the Japanese archipelago imminent, the possibility of additional atomic bombings, the Soviet entry into the war against Japan and its invasion of Manchuria, Japan announced its intention to surrender on 15 August 1945, cementing total victory in Asia for the Allies. Tribunals were set up by fiat by the Allies and war crimes trials were conducted in the wake of the war both against the Germans and the Japanese. World War II changed the political social structure of the globe; the United Nations was established to foster international co-operation and prevent future conflicts. The Soviet Union and United States emerged as rival superpowers, setting the stage for the nearly half-century long Cold War. In the wake of European devastation, the influence of its great powers waned, triggering the decolonisation of Africa and Asia.
Most countries whose industries had been damaged moved towards economic expansion. Political integration in Europe, emerged as an effort to end pre-war enmities and create a common identity; the start of the war in Europe is held to be 1 September 1939, beginning with the German invasion of Poland. The dates for the beginning of war in the Pacific include the start of the Second Sino-Japanese War on 7 July 1937, or the Japanese invasion of Manchuria on 19 September 1931. Others follow the British historian A. J. P. Taylor, who held that the Sino-Japanese War and war in Europe and its colonies occurred and the two wars merged in 1941; this article uses the conventional dating. Other starting dates sometimes used for World War II include the Italian invasion of Abyssinia on 3 October 1935; the British historian Antony Beevor views the beginning of World War II as the Battles of Khalkhin Gol fought between Japan and the fo
Artillery is a class of heavy military weapons built to fire munitions far beyond the range and power of infantry's small arms. Early artillery development focused on the ability to breach defensive walls, fortifications during sieges, led to heavy immobile siege engines; as technology improved, more mobile field artillery cannons developed for battlefield use. This development continues today. In its earliest sense, the word artillery referred to any group of soldiers armed with some form of manufactured weapon or armour. Since the introduction of gunpowder and cannon, the word "artillery" has meant cannon, in contemporary usage, it refers to shell-firing guns, howitzers and rocket artillery. In common speech, the word artillery is used to refer to individual devices, along with their accessories and fittings, although these assemblages are more properly called "equipments". However, there is no recognised generic term for a gun, mortar, so forth: the United States uses "artillery piece", but most English-speaking armies use "gun" and "mortar".
The projectiles fired are either "shot" or "shell". "Shell" is a used generic term for a projectile, a component of munitions. By association, artillery may refer to the arm of service that customarily operates such engines. In some armies one arm has operated field, anti-aircraft artillery and anti-tank artillery, in others these have been separate arms and in some nations coastal has been a naval or marine responsibility. In the 20th century technology based target acquisition devices, such as radar, systems, such as sound ranging and flash spotting, emerged to acquire targets for artillery; these are operated by one or more of the artillery arms. The widespread adoption of indirect fire in the early 20th century introduced the need for specialist data for field artillery, notably survey and meteorological, in some armies provision of these are the responsibility of the artillery arm. Artillery originated for use against ground targets—against infantry and other artillery. An early specialist development was coastal artillery for use against enemy ships.
The early 20th century saw the development of a new class of artillery for use against aircraft: anti-aircraft guns. Artillery is arguably the most lethal form of land-based armament employed, has been since at least the early Industrial Revolution; the majority of combat deaths in the Napoleonic Wars, World War I, World War II were caused by artillery. In 1944, Joseph Stalin said in a speech that artillery was "the God of War". Although not called as such, machines performing the role recognizable as artillery have been employed in warfare since antiquity. Historical references show artillery was first employed by the Roman legions at Syracuse in 399 BC; until the introduction of gunpowder into western warfare, artillery was dependent upon mechanical energy which not only limited the kinetic energy of the projectiles, it required the construction of large engines to store sufficient energy. A 1st-century BC Roman catapult launching 6.55 kg stones achieved a kinetic energy of 16,000 joules, compared to a mid-19th-century 12-pounder gun, which fired a 4.1 kg round, with a kinetic energy of 240,000 joules, or a late 20th century US battleship that fired a 1,225 kg projectile from its main battery with an energy level surpassing 350,000,000 joules.
From the Middle Ages through most of the modern era, artillery pieces on land were moved by horse-drawn gun carriages. In the contemporary era, artillery pieces and their crew relied on wheeled or tracked vehicles as transportation; these land versions of artillery were dwarfed by railway guns, which includes the largest super-gun conceived, theoretically capable of putting a satellite into orbit. Artillery used by naval forces has changed with missiles replacing guns in surface warfare. Over the course of military history, projectiles were manufactured from a wide variety of materials, into a wide variety of shapes, using many different methods in which to target structural/defensive works and inflict enemy casualties; the engineering applications for ordnance delivery have changed over time, encompassing some of the most complex and advanced technologies in use today. In some armies, the weapon of artillery is the projectile, not the equipment; the process of delivering fire onto the target is called gunnery.
The actions involved in operating an artillery piece are collectively called "serving the gun" by the "detachment" or gun crew, constituting either direct or indirect artillery fire. The manner in which gunnery crews are employed is called artillery support. At different periods in history this may refer to weapons designed to be fired from ground-, sea-, air-based weapons platforms; the term "gunner" is used in some armed forces for the soldiers and sailors with the primary function of using artillery. The gunners and their guns are grouped in teams called either "crews" or "detachments". Several such crews and teams with other functions are combined into a unit of artillery called a battery, although sometimes called a company. In gun detachments, each role is numbered, starting with "1" the Detachment Commander, the highest number being the Coverer, the second-in-command. "Gunner" is the lowest rank and junior non-commissioned officers are "Bombardiers" in some artillery arms. Batteries are equivalent to a company in the infantry
A bomb is an explosive weapon that uses the exothermic reaction of an explosive material to provide an sudden and violent release of energy. Detonations inflict damage principally through ground- and atmosphere-transmitted mechanical stress, the impact and penetration of pressure-driven projectiles, pressure damage, explosion-generated effects. Bombs have been utilized since the 11th century starting in East Asia; the term bomb is not applied to explosive devices used for civilian purposes such as construction or mining, although the people using the devices may sometimes refer to them as a "bomb". The military use of the term "bomb", or more aerial bomb action refers to airdropped, unpowered explosive weapons most used by air forces and naval aviation. Other military explosive weapons not classified as "bombs" include shells, depth charges, or land mines. In unconventional warfare, other names can refer to a range of offensive weaponry. For instance, in recent Middle Eastern conflicts, homemade bombs called "improvised explosive devices" have been employed by insurgent fighters to great effectiveness.
The word comes from the Latin bombus, which in turn comes from the Greek βόμβος, an onomatopoetic term meaning "booming", "buzzing". Explosive bombs were used by a Jurchen Jin army against a Chinese Song city. Bombs built using bamboo tubes appear in the 11th century. Bombs made of cast iron shells packed with explosive gunpowder date to 13th century China; the term was coined for this bomb during a Jin dynasty naval battle of 1231 against the Mongols. The History of Jin 《金史》 states that in 1232, as the Mongol general Subutai descended on the Jin stronghold of Kaifeng, the defenders had a "thunder-crash bomb" which "consisted of gunpowder put into an iron container... when the fuse was lit there was a great explosion the noise whereof was like thunder, audible for more than thirty miles, the vegetation was scorched and blasted by the heat over an area of more than half a mou. When hit iron armour was quite pierced through." The Song Dynasty official Li Zengbo wrote in 1257 that arsenals should have several hundred thousand iron bomb shells available and that when he was in Jingzhou, about one to two thousand were produced each month for dispatch of ten to twenty thousand at a time to Xiangyang and Yingzhou.
The Ming Dynasty text Huolongjing describes the use of poisonous gunpowder bombs, including the "wind-and-dust" bomb. During the Mongol invasions of Japan, the Mongols used the explosive "thunder-crash bombs" against the Japanese. Archaeological evidence of the "thunder-crash bombs" has been discovered in an underwater shipwreck off the shore of Japan by the Kyushu Okinawa Society for Underwater Archaeology. X-rays by Japanese scientists of the excavated shells confirmed. Explosive shock waves can cause situations such as body displacement, internal bleeding and ruptured eardrums. Shock waves produced by explosive events have two distinct components, the positive and negative wave; the positive wave shoves outward from the point of detonation, followed by the trailing vacuum space "sucking back" towards the point of origin as the shock bubble collapses. The greatest defense against shock injuries is distance from the source of shock; as a point of reference, the overpressure at the Oklahoma City bombing was estimated in the range of 28 MPa.
A thermal wave is created by the sudden release of heat caused by an explosion. Military bomb tests have documented temperatures of up to 2,480 °C. While capable of inflicting severe to catastrophic burns and causing secondary fires, thermal wave effects are considered limited in range compared to shock and fragmentation; this rule has been challenged, however, by military development of thermobaric weapons, which employ a combination of negative shock wave effects and extreme temperature to incinerate objects within the blast radius. This would be fatal to humans. Fragmentation is produced by the acceleration of shattered pieces of bomb casing and adjacent physical objects; the use of fragmentation in bombs dates to the 14th century, appears in the Ming Dynasty text Huolongjing. The fragmentation bombs were filled with iron pieces of broken porcelain. Once the bomb explodes, the resulting shrapnel is capable of piercing the skin and blinding enemy soldiers. While conventionally viewed as small metal shards moving at super-supersonic and hypersonic speeds, fragmentation can occur in epic proportions and travel for extensive distances.
When the SS Grandcamp exploded in the Texas City Disaster on April 16, 1947, one fragment of that blast was a two-ton anchor, hurled nearly two miles inland to embed itself in the parking lot of the Pan American refinery. Fragmentation should not be confused with shrapnel, which relies on the momentum of a shell to cause damage. To people who are close to a blast incident, such as bomb disposal technicians, soldiers wearing body armor, deminers, or individuals wearing little to no protection, there are four types of blast effects on the human body: overpressure, fragmentation and heat. Overpressure refers to the sudden and drastic rise in ambient pressure that can damage the internal organs leading to permanent damage or death. Fragmentation includes the shrapnel described above but can include sand and vegetation from the area surrounding the blast source; this is common in anti-personnel mine blasts. The projection of materials poses a lethal threat caused by cuts in soft tiss
An autocannon or automatic cannon is a large automatic, rapid-fire projectile weapon that fires armour-piercing or explosive shells, as opposed to the bullet fired by a machine gun. Autocannons have a larger calibre than a machine gun, but are smaller than a field gun or other artillery; when used on its own, the word "autocannon" indicates a single-barrel weapon. When multiple rotating barrels are involved, the word "rotary" is added, such a weapon is referred to as a "rotary autocannon". Modern autocannons are not single soldier-portable or stand-alone units, rather they are vehicle-mounted, aircraft-mounted, or boat-mounted, or remote-operated as in some naval applications; as such, ammunition is fed from a belt to reduce reloading or for a faster rate of fire, but a magazine remains an option. They can use a variety of ammunition: common shells include high-explosive dual-purpose types, any variety of armour-piercing types, such as composite rigid or discarding sabot types. Although capable of generating a high rate of fire, autocannons overheat if used for sustained fire, are limited by the amount of ammunition that can be carried by the weapons systems mounting them.
Both the US 25 mm Bushmaster and the British 30 mm Rarden have slow rates of fire so as not to use ammunition too quickly. The rate of fire of a modern autocannon ranges from 90 rounds per minute, to 2,500 rounds per minute with the GIAT 30. Systems with multiple barrels can have rates of fire of over 10,000 rounds per minute; such high rates of fire are employed by aircraft in air-to-air combat and close air support attacks on ground targets, where the target dwell time is short and weapons are operated in brief bursts. The first modern autocannon was the British QF 1 pounder known as the "pom-pom"; this was an upscaled version of the Maxim gun, the first successful automatic machine gun, requiring no outside stimulus in its firing cycle other than holding the trigger. The pom-pom fired 1 pound gunpowder-filled explosive shells at a rate of over 200 rounds a minute: much faster than conventional artillery while possessing a much longer range and more firepower than the infantry rifle. In 1913, Reinhold Becker and his Stahlwerke Becker firm designed the 20mm Becker cannon for the German Empire's perceived need for heavy-calibre aircraft armament, was assisted by the Imperial Government's Spandau Arsenal in perfecting the ordnance - although only about 500+ examples of the original Becker design were made during World War I, the design's patent was acquired by the Swiss Oerlikon Contraves firm in 1924, with the Third Reich's Ikaria-Werke firm of Berlin using Oerlikon design patents in creating the MG FF wingmount cannon ordnance, in Imperial Japan, their navy's adoption and production of the Type 99 cannon in 1939 was based on the Becker/Oerlikon design's principles.
During the First World War, autocannons were used in the trenches as an anti-aircraft gun. The British used pom-pom guns as part of their air defences to counter the German Zeppelin airships that made regular bombing raids on London, but they were of little value, as their shells neither ignited the hydrogen of the Zeppelins, nor caused sufficient loss of gas to bring them down. Attempts to use them in aircraft failed as the weight limited both speed and altitude, thus making successful interception impossible; the more effective QF 2 pounder naval gun would be developed during the war to serve as an anti-aircraft and close range defensive weapon for naval vessels. Autocannons would serve in a much greater capacity during the Second World War. During the inter-war years, aircraft underwent an evolution and the all-metal monoplane, pioneered as far back as the end of 1915 replaced wood and fabric biplanes; the subsequent increase in speed and durability reduced the window of opportunity for defence.
Heavier anti-aircraft cannon had difficulty tracking fast-moving aircraft and were unable to judge altitude or distance, while machine guns possessed insufficient range and firepower to bring down aircraft consistently. Weapons such as the Oerlikon 20 mm and the Bofors 40 mm would see widespread use by both sides during the second World War. Continued ineffectiveness against aircraft despite the large numbers installed during the second World War led, in the West, to the removal of all shipboard anti-aircraft weapons in the early post-war period; this was only reversed with the introduction of computer-controlled systems. The German Panzer II light tank, one of the most numerous in German service during the invasion of Poland and the campaign in France, used a 20 mm autocannon as its main armament. Although ineffective against tank armour during the early years of the war, the cannon was effective against light-skinned vehicles as well as infantry and was used by armoured cars. Larger examples, such as the 40 mm Vickers S, were mounted in ground attack aircraft to serve as an anti-tank weapon, a role to which they were suited as tank armour is lightest on top.
Polish 20 mm. Unlike the Oerlikon, it was effective against all the tanks fielded in 1939 because it was built as an upgrade to the Oerlikon, Hispano—Suiza, Madsen. It, with great difficulty, proved capable of knocking out early Panzer IIIs and IVs. Only 55 were produced by the time of the Polish Defensive War. In airc