The Hanriot H.25 was a French, single-engined, six passenger airliner built in 1926. Only one was flown; the Hanriot H.25 was a braced, high wing monoplane. It had an all-metal structure, covered everywhere with fabric, its wing was built in three parts, a central section fixed to the upper fuselage longerons and a pair of outer panels which were braced on each side by two sets of parallel paired, interconnected struts which ran from two well-separated positions on the wing spars to meet on the undercarriage structure. The wing was rectangular in plan apart from angled tops and had constant thickness. Narrow-chord ailerons filled well over half the trailing edge, it was powered by eighteen cylinder Salmson 18 Cm. This was one of the last, the most powerful, of Salmson's water-cooled radial engines, with two in-line rows of nine cylinders, it was enclosed in a rounded cowling with caps over the cylinder-heads. Fuel was held in the wing centre-section and two Lamblin radiators were mounted on the undercarriage legs.
Behind the engine the fuselage was rectangular in section, defined by light-metal, U-section longerons and cross-frames. The open cockpit was with small side-windows for a better view downwards. Behind the cockpit the cabin seated each with their own window. Entry was via a port-side door and there was a disposable emergency ceiling hatch to allow passengers to escape by parachute; the horizontal tail was mounted on top of the fuselage, braced from the lower fuselage longerons on each side with a pair of parallel struts. Its plan was similar to the wing and the elevators were split, with a cut-out for the deep, broad rudder; the tailplane angle of incidence could be trimmed in flight. The low area fin was broad but unusually low; the H.28 had conventional, tailskid landing gear. Its mainwheels, half enclosed by individual semi-circular fairings, were on a single axle and rubber cord shock absorbers enclosed within a streamlined fairing mounted on the lower fuselage longerons by N-form struts and reinforced by the wing bracing struts.
The undercarriage track was 3 m. The date of the H.28's first flight is not known but by mid-May 1926 its development programme was underway at Villacoublay. No more independent reports on the type appear in the French journals and there is no evidence of a second example. Data from Les Ailes, May 1926General characteristics Crew: one Capacity: six passengers Length: 12.50 m Wingspan: 17.0 m Height: 3.80 m Wing area: 51 m2 Empty weight: 1,700 kg Gross weight: 2,600 kg Fuel capacity: Fuel and oil 300 kg Powerplant: 1 × Salmson 18 Cm water-cooled, two row inline radial, 370 kW Propellers: 2-bladedPerformance Maximum speed: 195 km/h at ground level Service ceiling: 4,000 m
Aéroplanes Hanriot et Cie. or simply'Hanriot' was a French aircraft manufacturer with roots going back to the beginning of aviation. Founded by René Hanriot in 1910 as The Monoplans Hanriot Company Ltd. the company survived in different forms until 1916 when it established itself with the Hanriot-Dupont fighters and observation aircraft. The company lasted through several takeovers and structural changes until in 1936 it merged with Farman to become the Société Nationale de Constructions Aéronautiques du Centre.'Central Air Works' consortium. Hanriot aeroplanes included pre-war monoplanes with boat-like fuselages, the HD.1 and 2 World War I biplane fighters, the HD.14 trainer, the H.220 series of twin-engined heavy fighters that evolved in the SNCAC 600 fighter just before World War II. The company's main bases of operations were Bétheny Boulogne-Billancourt, Carrières-sur-Seine and Bourges. René Hanriot, a builder and racer of motor boats and a race car driver for the Darracq motor company, built his first aircraft in 1907, although it did not fly until late 1909.
It was a monoplane with a wire-braced wooden fuselage resembling the Blériot XI but was immediately superseded by a series of similar monoplanes, which were exhibited at the Brussels Salon d'Automobiles, d'Aeronautique, du Cycles et dus Sports in January 1910. These featured a slender wooden monocoque fuselage and were powered by a 20 hp Darracq and a 40 hp Gyp. and a handful were built. Together with Darracq racing colleague Louis Wagner, Hanriot started a flying school at Bétheny near Reims, where the Hanriot factory was located. Unusually, Hanriot tested new design features using a flying model powered by a 2 kW Duthiel-Chalmers. In 1910 Hanriot and his staff pilots made regular appearances at air shows in England. Hanriot's 15-year-old son Marcel became the youngest holder of a pilot's certificate, joined his father's pilots as a competition flyer. René Hanriot withdrew from competition flying himself and concentrated on constructing aircraft. Hanriot's 1911 military two-seater was passed over at the French military trials, among other reasons because its fuselage was so slender that the crew were unshielded.
It was obsolete and never had a serious chance against contemporary Nieuport, Morane-Saulnier and Deperdussin types. Nieuport's former chief engineer Alfred Pagny designed the 1912 Hanriot, the Nieuport influence was visible, but it failed to gain any orders at the 1912 military trials and attempts to sell them were unsuccessful. Faced with bankruptcy, René Hanriot sold his assets to Louis Alfred Ponnier, who reorganized the company as the Société de Construction de Machines pour la Navigation Aérienne, headed by Pagny. In 1913, Marcel Hanriot, now 18, was called up for military service; the Ponnier factory continued for several years to develop the monoplane racer, one of, placed second in the 1913 Gordon Bennett Trophy competition. Following the outbreak of World War I, Marcel Hanriot, still in military service, flew French air force bombers; the German advance stalled with the CMNA/Ponnier factories in Rheims behind German lines, but René Hanriot founded a new factory, Aéroplanes Hanriot et Cie, in Levallois.
Starting as a subcontractor building airplane components, the company progressed to licence-build aircraft from other manufacturers. In 1915, Marcel Hanriot, after being wounded in a night-flying raid, was released from military service and joined his father's factory. Around the same time, Hanriot hired the young engineer Emile Dupont and in 1916, the Dupont-designed fighter HD.1 was produced. Although being passed over by the French air force in favor of the more powerful SPAD VII design, the HD.1 was ordered by the Belgian and Italian air force. Heavy demand resulted in a new factory being opened in Boulogne-Billancourt. Licences to build the HD.1 were sold to Macchi in Italy. Hanriot employed 2000 workers in his Boulogne-Billancourt factory alone. After the war, Hanriot continued as a manufacturer of fighters and all-purpose aircraft, building on the HD.1 / HD.2 series but bringing out new biplane and monoplane designs. In 1924, having outgrown its Boulogne-Billancourt works, the company moved to Carrières-sur-Seine René Hanriot died on 7 November 1925.
His heirs and his two brothers-in-law, entrusted daily operations of the factories to Outhenin Chalandre director of a paper mill. In 1930 the Hanriot company became part of the Lorraine-Dietrich company under the name Lorraine-Hanriot; the merger lasted three years, until in 1933 the two companies separated and Marcel Hanriot stepped once again forward to lead his family business. Under his management, the company embarked on an ambitious project to design and build state-of-the-art metal military aircraft like the H.220 heavy fighter. However its main successes would be with the liaison/training monoplane H.180/H.182 and the twin-engined H.232/H.232 trainer In 1936 the company was included in Pierre Cot's nationalisation programme, Merging with Farman to become the Société Nationale de Constructions Aéronautiques du Centre in 1937. Unlike Maurice Farman, who left the new company in protest, Marcel Hanriot stayed on as one of the directors; the pre-war aircraft designed by René Hanriot went by Roman Numerals, the 1907 monoplane being the'Type I'.
However the planes were known by a description featuring the year of built and some characteristic such as'monoplane', one- or two-seater and horsepower. Thus Hanriot's first airplane was the'1907 monoplane', the type IV was the'1911 military two-seater' and the Hanriot VIII was known as the'Hanriot 100 ch' (100 Hp Hanrio
An aileron is a hinged flight control surface forming part of the trailing edge of each wing of a fixed-wing aircraft. Ailerons are used in pairs to control the aircraft in roll, which results in a change in flight path due to the tilting of the lift vector. Movement around this axis is called'rolling' or'banking'; the modern aileron was invented and patented by the British scientist Matthew Piers Watt Boulton in 1868, based on his 1864 paper On Aërial Locomotion. Though there was extensive prior art in the 19th century for the aileron and its functional analog, wing warping, in 1906 the United States granted an expansive patent to the Wright Brothers of Dayton, for the invention of a system of aerodynamic control that manipulated an airplane's control surfaces. Considerable litigation ensued within the United States over the legal issues of lateral roll control, until the First World War compelled the U. S. Government to legislate a legal resolution; the name "aileron", from French, meaning "little wing" refers to the extremities of a bird's wings used to control their flight.
It first appeared in print in the 7th edition of Cassell's French-English Dictionary of 1877, with its lead meaning of "small wing". In the context of powered airplanes it appears in print about 1908. Prior to that, ailerons were referred to as rudders, their older technical sibling, with no distinction between their orientations and functions, or more descriptively as horizontal rudders. Among the earliest printed aeronautical use of'aileron' was that in the French aviation journal L'Aérophile of 1908. Ailerons had more or less supplanted other forms of lateral control, such as wing warping, by about 1915, well after the function of the rudder and elevator flight controls had been standardised. Although there were many conflicting claims over who first invented the aileron and its function, i.e. lateral or roll control, the flight control device was invented and described by the British scientist and metaphysicist Matthew Piers Watt Boulton in his 1864 paper On Aërial Locomotion. He was the first to patent an aileron control system in 1868.
Boulton's description of his lateral flight control system was both complete. It was "the first record we have of appreciation of the necessity for active lateral control as distinguished from.... With this invention of Boulton's we have the birth of the present-day three torque method of airborne control" as was praised by Charles Manly; this was endorsed by C. H. Gibbs-Smith. Boulton's British patent, No. 392 of 1868, issued about 35 years before ailerons were "reinvented" in France, became forgotten and lost from sight until after the flight control device was in general use. Gibbs-Smith stated on several occasions that if the Boulton patent had been revealed at the time of the Wright brothers' legal filings, they might not have been able to claim priority of invention for the lateral control of flying machines; the fact that the Wright brothers were able to gain a patent in 1906 did not invalidate Boulton's lost and forgotten invention. Boulton had described and patented ailerons in 1868 and they were not used on manned aircraft until they were employed on Robert Esnault-Pelterie’s glider in 1904, although in 1871 a French military engineer, Charles Renard and flew an unmanned glider incorporating ailerons on each side, activated by a Boulton-style pendulum controlled single-axis autopilot device.
The pioneering U. S. aeronautical engineer Octave Chanute published descriptions and drawings of the Wright brothers' 1902 glider in the leading aviation periodical of the day, L'Aérophile, in 1903. This prompted Esnault-Pelterie, a French military engineer, to build a Wright-style glider in 1904 that used ailerons in lieu of wing warping; the French journal L’Aérophile published photos of the ailerons on Esnault-Pelterie’s glider which were included in his June 1905 article, its ailerons were copied afterward. The Wright brothers used wing warping instead of ailerons for roll control on their glider in 1902, about 1904 their Flyer II was the only aircraft of its time able to do a coordinated banked turn. During the early years of powered flight the Wrights had better roll control on their designs than airplanes that used movable surfaces. From 1908, as aileron designs were refined it became clear that ailerons were much more effective and practical than wing warping. Ailerons had the advantage of not weakening the airplane's wing structure as did the wing warping technique, one reason for Esnault-Pelterie's decision to switch to ailerons.
By 1911 most biplanes used ailerons rather than wing warping—by 1915 ailerons had become universal on monoplanes as well. The U. S. Government, frustrated by the lack of its country's aeronautical advances in the years leading up to World War I, enforced a patent pool putting an end to the Wright brothers patent war; the Wright company changed its aircraft flight controls from wing warping to the use of ailerons at that time as well. Others who were thought to have been the first to introduce ailerons included: American John J. Montgomery included spring-loaded trailing edge flaps on his second glider: these were operable by the pilot as ailerons. In 1886 his third glider design used rotation of the entire wing rather than just a trailing edge portion for roll control. By his own accounts all of these changes in addition to his use of an elevator for pitch control provided "entire control of the machine in the wind, preventing it from upsetting." New Zealander Richard Pearse reputedly made a power
A synchronization gear, or a gun synchronizer, sometimes rather less called an interrupter, is attached to the armament of a single-engine tractor-configuration aircraft so it can fire through the arc of its spinning propeller without bullets striking the blades. The idea presupposes a fixed armament directed by aiming the aircraft in which it is fitted at the target, rather than aiming the gun independently. There are many practical problems arising from the inherently imprecise nature of an automatic gun's firing, the great velocity of the blades of a spinning propeller, the high speed at which any gear synchronizing the two has to operate. Design and experimentation with gun synchronization had been underway in France and Germany in 1913–1914, following the ideas of August Euler, who seems to have been the first to suggest mounting a fixed armament firing in the direction of flight. However, the first practical—if far from reliable—gear to enter operational service was that fitted to the Eindecker monoplane fighters, which entered squadron service with the German Air Service in mid-1915.
The success of the Eindecker led to numerous gun synchronization devices, culminating in the reasonably reliable hydraulic British Constantinesco gear of 1917. By the end of the war German engineers were well on the way to perfecting a gear using an electrical rather than a mechanical or hydraulic link between the engine and the gun, with the gun being triggered by a solenoid rather than by a mechanical "trigger motor". From 1918 to the mid-1930s the standard armament for a fighter aircraft remained two synchronized rifle calibre machine guns, firing forward through the propeller. During the late-1930s, the main role of the fighter was seen as the destruction of large, all-metal bombers, for which the "traditional" light armament was inadequate. Since it was impractical to try to fit more than one or two extra guns in the limited space available in the front of a single-engine aircraft's fuselage, this led to an increasing proportion of the armament being mounted in the wings, firing outside the arc of the propeller.
There were in fact some advantages in dispensing with centrally mounted guns altogether. The conclusive redundancy of synchronization gears did not come until the introduction of jet propulsion and the absence of a propeller for guns to be synchronized with. From the beginnings of practical flight possible military uses for aircraft were considered, although not all writers came to positive conclusions on the subject. By 1913 military exercises in Britain and France had confirmed the usefulness of aircraft for reconnaissance and surveillance, this was seen by a few forward looking officers as implying the need to deter or destroy the enemy's reconnaissance machines, thus aerial combat was by no means unanticipated, the machine gun was from the first seen as the most weapon to be used. "It is that an aircraft, capable of shooting at an enemy machine will have the advantage. The most suitable weapon is a light, air-cooled machine-gun". What was not agreed on was the superiority, at least for an attacking aircraft, of fixed forward-firing guns, aimed by pointing the aircraft at its target, rather than flexible weapons, aimed by a gunner other than the pilot.
"The idea of coupling the firing mechanism to the propeller's rotation is an affectation. The objection is the same as to any gun position, fixed along the longitudinal axis of the aircraft: the pilot is forced to fly directly at the enemy in order to fire. Under certain circumstances this is undesirable"; as late as 1916, pilots of the DH.2 pusher fighter had problems convincing their senior officers that the forward-firing armament of their aircraft was more effective if it was fixed to fire forward rather than being flexible. On the other hand, August Euler had patented the idea of a fixed gun as early as 1910 – long before tractor aircraft became the norm, illustrating his patent with a diagram of a machine gun-armed pusher. A mechanism to enable an automatic weapon to fire between the blades of a whirling propeller is called an interrupter or synchronizer gear. Both these terms are more or less misleading, at least insofar as explaining what happens when the gear functions; the term "interrupter" implies that the gear pauses, or "interrupts" the fire of the gun at the point where one of the blades of the propeller passes in front of its muzzle.
The difficulty is that the slowly revolving propellers of First World War aircraft turned twice or three times for each shot a contemporary machine gun could fire. A two-bladed propeller would therefore obstruct the gun six times every firing cycle of the gun, a four-bladed one twelve times. Another way of putting this is that an "interrupted" gun would have been "blocked" more than forty times every second, while it was firing at a rate in the region of seven rounds per second. Unsurprisingly, the designers of so-called interrupter gears found this too problematic to be attempted, the gaps between "interruptions" would have been too short to allow the gun to fire at all, and yet, "synchronization", in the usual sense of the word, between the rate of fire of a machine gun and the revolutions per minute of a spinning aircraft propeller is a conceptual impossibility. A machine gun fires a constant number of rounds a minute, while this may be boosted by, for instance and increasing the tension on a return spring, or redirecting the gasses produced by each firing, it cannot be varied at w
A fighter aircraft is a military aircraft designed for air-to-air combat against other aircraft, as opposed to bombers and attack aircraft, whose main mission is to attack ground targets. The hallmarks of a fighter are its speed and small size relative to other combat aircraft. Many fighters have secondary ground-attack capabilities, some are designed as dual-purpose fighter-bombers; this may be for national security reasons, for advertising purposes, or other reasons. A fighter's main purpose is to establish air superiority over a battlefield. Since World War I, achieving and maintaining air superiority has been considered essential for victory in conventional warfare; the success or failure of a belligerent's efforts to gain air superiority hinges on several factors including the skill of its pilots, the tactical soundness of its doctrine for deploying its fighters, the numbers and performance of those fighters. Because of the importance of air superiority, since the early days of aerial combat armed forces have competed to develop technologically superior fighters and to deploy these fighters in greater numbers, fielding a viable fighter fleet consumes a substantial proportion of the defense budgets of modern armed forces.
The word "fighter" did not become the official English-language term for such aircraft until after World War I. In the British Royal Flying Corps and Royal Air Force these aircraft were referred to as "scouts" into the early 1920s; the U. S. Army called their fighters "pursuit" aircraft from 1916 until the late 1940s. In most languages a fighter aircraft is known as hunting aircraft. Exceptions include Russian, where a fighter is an "истребитель", meaning "exterminator", Hebrew where it is "matose krav"; as a part of military nomenclature, a letter is assigned to various types of aircraft to indicate their use, along with a number to indicate the specific aircraft. The letters used to designate a fighter differ in various countries – in the English-speaking world, "F" is now used to indicate a fighter, though when the pursuit designation was used in the US, they were "P" types. In Russia "I" was used, while the French continue to use "C". Although the term "fighter" specifies aircraft designed to shoot down other aircraft, such designs are also useful as multirole fighter-bombers, strike fighters, sometimes lighter, fighter-sized tactical ground-attack aircraft.
This has always been the case, for instance the Sopwith Camel and other "fighting scouts" of World War I performed a great deal of ground-attack work. In World War II, the USAAF and RAF favored fighters over dedicated light bombers or dive bombers, types such as the Republic P-47 Thunderbolt and Hawker Hurricane that were no longer competitive as aerial combat fighters were relegated to ground attack. Several aircraft, such as the F-111 and F-117, have received fighter designations though they had no fighter capability due to political or other reasons; the F-111B variant was intended for a fighter role with the U. S. Navy, but it was cancelled; this blurring follows the use of fighters from their earliest days for "attack" or "strike" operations against ground targets by means of strafing or dropping small bombs and incendiaries. Versatile multirole fighter-bombers such as the McDonnell Douglas F/A-18 Hornet are a less expensive option than having a range of specialized aircraft types; some of the most expensive fighters such as the US Grumman F-14 Tomcat, McDonnell Douglas F-15 Eagle, Lockheed Martin F-22 Raptor and Russian Sukhoi Su-27 were employed as all-weather interceptors as well as air superiority fighter aircraft, while developing air-to-ground roles late in their careers.
An interceptor is an aircraft intended to target bombers and so trades maneuverability for climb rate. Fighters were developed in World War I to deny enemy aircraft and dirigibles the ability to gather information by reconnaissance over the battlefield. Early fighters were small and armed by standards, most were biplanes built with a wooden frame covered with fabric, a maximum airspeed of about 100 mph; as control of the airspace over armies became important, all of the major powers developed fighters to support their military operations. Between the wars, wood was replaced in part or whole by metal tubing, aluminium stressed skin structures began to predominate. On 15 August 1914, Miodrag Tomić encountered an enemy plane while conducting a reconnaissance flight over Austria-Hungary; the Austro-Hungarian aviator waved at Tomić, who waved back. The enemy pilot took a revolver and began shooting at Tomić's plane. Tomić fired back, he swerved away from the Austro-Hungarian plane and the two aircraft parted ways.
It was considered the first exchange of fire between aircraft in history. Within weeks, all Serbian and Austro-Hungarian aircraft were armed; the Serbians equipped their planes with 8-millimetre Schwarzlose MG M.07/12 machine guns, six 100-round boxes of ammunition and several bombs. By World War II, most fighters were all-metal monoplanes armed with batteries of machine guns or cannons and some were capable of speeds approaching 400 mph. Most fighters up to this point had one engine.
The Ponnier D. III was a French monoplane racing aircraft, designed to compete in the 1913 Gordon Bennett Trophy race, it finished a close second. During 1911 René Hanriot hired Alfred Pagny at Nieuport, as a designer. After Hanriot military prototypes failed to win orders at the Concours Militaire in late 1911 he sold his aircraft interests to another of his designers, Louis Alfred Ponnier. Pagny designed two similar single seat monoplanes for Hanriot and Ponnier, the Hanriot D. I and the Ponnier D. III. III, his designs reflected Nieuport practice with the replacement of Hanriot's graceful boat-like shell fuselages with flat sided, deep chested ones. The Ponnier D. III was a single seat, mid wing monoplane designed to compete in the 1913 Gordon Bennett Trophy race. Pairs of landing wires on each side met over the fuselage at a pyramidal four strut pylon and parallel flying wires went to the lower fuselage. An oil deflecting cowling, open at the bottom, surrounded the powerful double row, fourteen cylinder Gnome Lambda-Lambda rotary engine, which delivered 160 hp to a 2 m diameter propeller.
The oval, open cockpit was placed at just aft of the pylon centre. It had a finless rudder at the extreme rear of the fuselage and a straight edged tailplane mounted on the upper fuselage ahead of it; the elevators were interconnected, controlled by central wires. The D. III had a fixed, conventional undercarriage with mainwheels on a single axle mounted to the fuselage by pairs of wire cross-braced V-struts, plus a simple elliptical leaf spring tailskid. Jane's All the World's Aircraft 1913 describes a longer Hanriot D. III with a 100 hp Gnome engine; the D. III participated in the Gordon-Bennett Trophy race piloted by Emile Védrines; the elimination race over 100 km left four aircraft in the final, flown over 200 km on Monday 29 September. After an hour's flight the Ponnier finished second, just 66 seconds behind Maurice Prévost in a Deperdussin Monocoque. Data from Flight 22 November 1913General characteristics Crew: One Length: 5.41 m Wingspan: 7.16 m Wing area: 8.7 m2 Gross weight: 500 kg Powerplant: 1 × Gnome Lambda-Lambda 14-cylinder, two row rotary engine, 120 kW Propellers: 2-bladed, 2.08 m diameterPerformance Maximum speed: 200 km/h
World War I
World War I known as the First World War or the Great War, was a global war originating in Europe that lasted from 28 July 1914 to 11 November 1918. Contemporaneously described as "the war to end all wars", it led to the mobilisation of more than 70 million military personnel, including 60 million Europeans, making it one of the largest wars in history, it is one of the deadliest conflicts in history, with an estimated nine million combatants and seven million civilian deaths as a direct result of the war, while resulting genocides and the 1918 influenza pandemic caused another 50 to 100 million deaths worldwide. On 28 June 1914, Gavrilo Princip, a Bosnian Serb Yugoslav nationalist, assassinated the Austro-Hungarian heir Archduke Franz Ferdinand in Sarajevo, leading to the July Crisis. In response, on 23 July Austria-Hungary issued an ultimatum to Serbia. Serbia's reply failed to satisfy the Austrians, the two moved to a war footing. A network of interlocking alliances enlarged the crisis from a bilateral issue in the Balkans to one involving most of Europe.
By July 1914, the great powers of Europe were divided into two coalitions: the Triple Entente—consisting of France and Britain—and the Triple Alliance of Germany, Austria-Hungary and Italy. Russia felt it necessary to back Serbia and, after Austria-Hungary shelled the Serbian capital of Belgrade on the 28th, partial mobilisation was approved. General Russian mobilisation was announced on the evening of 30 July; when Russia failed to comply, Germany declared war on 1 August in support of Austria-Hungary, with Austria-Hungary following suit on 6th. German strategy for a war on two fronts against France and Russia was to concentrate the bulk of its army in the West to defeat France within four weeks shift forces to the East before Russia could mobilise. On 2 August, Germany demanded free passage through Belgium, an essential element in achieving a quick victory over France; when this was refused, German forces invaded Belgium on 3 August and declared war on France the same day. On 12 August and France declared war on Austria-Hungary.
In November 1914, the Ottoman Empire entered the war on the side of the Alliance, opening fronts in the Caucasus and the Sinai Peninsula. The war was fought in and drew upon each power's colonial empire as well, spreading the conflict to Africa and across the globe; the Entente and its allies would become known as the Allied Powers, while the grouping of Austria-Hungary and their allies would become known as the Central Powers. The German advance into France was halted at the Battle of the Marne and by the end of 1914, the Western Front settled into a battle of attrition, marked by a long series of trench lines that changed little until 1917. In 1915, Italy opened a front in the Alps. Bulgaria joined the Central Powers in 1915 and Greece joined the Allies in 1917, expanding the war in the Balkans; the United States remained neutral, although by doing nothing to prevent the Allies from procuring American supplies whilst the Allied blockade prevented the Germans from doing the same the U. S. became an important supplier of war material to the Allies.
After the sinking of American merchant ships by German submarines, the revelation that the Germans were trying to incite Mexico to make war on the United States, the U. S. declared war on Germany on 6 April 1917. Trained American forces would not begin arriving at the front in large numbers until mid-1918, but the American Expeditionary Force would reach some two million troops. Though Serbia was defeated in 1915, Romania joined the Allied Powers in 1916 only to be defeated in 1917, none of the great powers were knocked out of the war until 1918; the 1917 February Revolution in Russia replaced the Tsarist autocracy with the Provisional Government, but continuing discontent at the cost of the war led to the October Revolution, the creation of the Soviet Socialist Republic, the signing of the Treaty of Brest-Litovsk by the new government in March 1918, ending Russia's involvement in the war. This allowed the transfer of large numbers of German troops from the East to the Western Front, resulting in the German March 1918 Offensive.
This offensive was successful, but the Allies rallied and drove the Germans back in their Hundred Days Offensive. Bulgaria was the first Central Power to sign an armistice—the Armistice of Salonica on 29 September 1918. On 30 October, the Ottoman Empire capitulated. On 4 November, the Austro-Hungarian empire agreed to the Armistice of Villa Giusti after being decisively defeated by Italy in the Battle of Vittorio Veneto. With its allies defeated, revolution at home, the military no longer willing to fight, Kaiser Wilhelm abdicated on 9 November and Germany signed an armistice on 11 November 1918. World War I was a significant turning point in the political, cultural and social climate of the world; the war and its immediate aftermath sparked numerous uprisings. The Big Four (Britain, the United States, It