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56-814: The first military uses of aviation involved lighter-than-air balloons. During the Battle of Fleurus in 1794, the French observation balloon l'Entreprenant was used to monitor Austrian troop movements. The use of lighter-than-air aircraft in warfare became prevalent in the 19th century, including regular use in the American Civil War . Lighter-than-air military aviation persisted until shortly after World War II , gradually being withdrawn from various roles as heavier-than-air aircraft improved. Heavier-than-air aircraft were recognized as having military applications early on, despite resistance from traditionalists and

112-519: A decisive contribution until the Germans introduced Blitzkrieg during the Invasion of Poland and Battle of France , where aircraft functioned as mobile flying artillery to quickly disrupt defensive formations. The Allies would later use rocket-equipped fighters in the same role, immobilizing German armored divisions during the Battle of Normandy and afterwards. World War I also saw the creation of

168-420: A lifting gas at temperatures above its boiling point of 25.6 °C. Its extreme toxicity, low buoyancy, and low boiling point have precluded such a use. Neon is lighter than air (density 0.900 g/L at STP, average atomic mass 20.17 g/mol) and could lift a balloon. Like helium, it is non-flammable. However, it is rare on Earth and expensive, and is among the heavier lifting gases. Pure nitrogen has

224-556: A major role in winning the Battle of the Atlantic . Aircraft also played a much expanded role, with many notable engagements being decided solely through the use of military aircraft, such as the Battle of Britain or the attack on Pearl Harbor , and the conclusion of the Pacific War against Japan was marked by two lone aircraft dropping the atomic bombs , devastating the cities of Hiroshima and Nagasaki . The introduction of

280-425: A nation's armed forces may use aviation ( naval aviation and army aviation ), in addition to or instead of, a dedicated air force. In some cases, this includes coast guard services that are also an armed service, as well as gendarmeries and equivalent forces. Lighter-than-air A lifting gas or lighter-than-air gas is a gas that has a density lower than normal atmospheric gases and rises above them as

336-456: A result, making it useful in lifting lighter-than-air aircraft. Only certain lighter than air gases are suitable as lifting gases. Dry air has a density of about 1.29 g/L (gram per liter) at standard conditions for temperature and pressure (STP) and an average molecular mass of 28.97  g/mol , and so lighter-than-air gases have a density lower than this. Heated atmospheric air is frequently used in recreational ballooning . According to

392-415: A ship with four vacuum spheres. In a theoretically perfect situation with weightless spheres, a "vacuum balloon" would have 7% more net lifting force than a hydrogen-filled balloon, and 16% more net lifting force than a helium-filled one. However, because the walls of the balloon must remain rigid without imploding, the balloon is impractical to construct with any known material. Despite that, sometimes there

448-502: A small explosive at the location of the ship, recording the time it took for the sound of the explosion to reach distant hydrophones mounted at shore stations or aboard crewed station ships, and radioing the time of receipt of the sound to the ship, allowing the crew to make precise position fixes by using triangulation . In 1931, the Coast and Geodetic Survey proposed the replacement of crewed station ships with "radio-sonobuoys", and placed

504-551: A sonar transducer, batteries, a radio transmitter and whip antenna, within a self-contained air-deployed floating (sono)buoy. Early sonobuoys had limited range, limited battery life and were overwhelmed by the noise of the ocean. They first appeared during World War II, in which they first were used in July 1942 by RAF Coastal Command under the code name 'High Tea', the first squadron to use them operationally being No. 210 Squadron RAF , operating Sunderlands . They were also limited by

560-490: A type of deep-sea submersibles that use gasoline as the "lifting gas". A balloon can only have buoyancy if there is a medium that has a higher average density than the balloon itself. In 2002, aerogel held the Guinness World Record for the least dense (lightest) solid. Aerogel is mostly air because its structure is like that of a highly vacuous sponge . The lightness and low density is due primarily to

616-407: Is at sea level at 0 °C. For higher altitudes, or higher temperatures, the amount of lift will decrease proportionally to the air density, but the ratio of the lifting capability of hydrogen to that of helium will remain the same. This calculation does not include the mass of the envelope need to hold the lifting gas. At higher altitudes, the air pressure is lower and therefore the pressure inside

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672-420: Is discussion on the topic. While not a gas, it is possible to synthesize an ultralight aerogel with a density less than air, the lightest recorded so far reaching a density approximately 1/6th that of air. Aerogels don't float in ambient conditions, however, because air fills the pores of an aerogel's microstructure, so the apparent density of the aerogel is the sum of the densities of the aerogel material and

728-415: Is extremely corrosive, highly toxic, expensive, is heavier than other lifting gases, and has a low boiling point of 19.5 °C. Its use would therefore be impractical. Acetylene is 10% lighter than air and could be used as a lifting gas. Its extreme flammability and low lifting power make it an unattractive choice. Hydrogen cyanide , which is 7% lighter than air, is technically capable of being used as

784-430: Is relatively heavy (density 0.769 g/L at STP, average molecular mass 17.03 g/mol), poisonous, an irritant, and can damage some metals and plastics. Methane (density 0.716 g/L at STP, average molecular mass 16.04 g/mol), the main component of natural gas , is sometimes used as a lift gas when hydrogen and helium are not available. It has the advantage of not leaking through balloon walls as rapidly as

840-458: Is slightly lighter than molecular nitrogen with a molecular mass of 27.7. Being pyrophoric it is however a major safety hazard, on a scale even greater than that of hydrogen. Theoretically, an aerostatic vehicle could be made to use a vacuum or partial vacuum. As early as 1670, over a century before the first manned hot-air balloon flight, the Italian monk Francesco Lana de Terzi envisioned

896-448: Is that this gas is noncombustible. But the use of helium has some disadvantages, too: In the past, coal gas , a mixture of hydrogen, carbon monoxide , and other gases, was also used in balloons. It was widely available and cheap. Disadvantages include a higher density (reducing lift), its flammability and the high toxicity of the carbon monoxide content. Ammonia has been used as a lifting gas in balloons, but while inexpensive, it

952-662: Is the branch of a nation's armed forces that is responsible for aerial warfare as distinct from the army , navy , or other branches. Most nations either maintain an air force or, in the case of smaller and less well-developed countries, an air wing (see List of air forces ). Air forces are usually tasked with the air defense of a country, as well as strategic bombing, interdiction, close air support, intelligence gathering, battlespace management, transport functions, and providing services to civil government agencies. Air force operations may also include space-based operations such as reconnaissance or satellite operations. Other branches of

1008-467: Is therefore already 200 years old. The biggest challenge has always been to make a material that can resist it. In 2003, a university team in Berlin, Germany, has successfully made a 150 °C steam lifted balloon. However, such a design is generally impractical due to high boiling point and condensation. Hydrogen fluoride is lighter than air and could theoretically be used as a lifting gas. However, it

1064-500: Is variable, depending on environmental conditions and the search pattern. The buoy relays acoustic information from its hydrophone(s) via UHF / VHF radio to operators on board the aircraft. With the technological improvement of the submarine in modern warfare, the need for an effective tracking system was born. Sound Navigation And Ranging ( SONAR ) was originally developed by the British—;who called it ASDIC —in

1120-408: Is very strong. The type of gas used is largely inconsequential because the relative differences between gases is negligible in relation to the density of water. However, some gases can liquefy under high pressure, leading to an abrupt loss of buoyancy. A submerged balloon that rises will expand or even explode because of the strong pressure reduction, unless gas is allowed to escape continuously during

1176-667: The Gulf War . Airborne Early Warning provides advance warning of enemy activities to reduce the chance of being surprised. Many also have command functions that allow them to direct or vector friendly fighters onto incoming bogeys. Bombers are capable of carrying large payloads of bombs and may sacrifice speed or maneuverability to maximize payload. Experimental aircraft are designed to test advanced aerodynamic, structural, avionic, or propulsion concepts. These are usually well instrumented, with performance data telemetered on radio-frequency data links to ground stations located at

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1232-406: The ideal gas law , an amount of gas (and also a mixture of gases such as air) expands as it is heated. As a result, a certain volume of gas has a lower density as the temperature is higher. The temperature of the hot air in the envelope will vary depending upon the ambient temperature, but the maximum continuous operating temperature for most balloons is 250 °F (121 °C). Hydrogen , being

1288-589: The jet engine , radar , early missiles , helicopters , and computers are World War II advancements which are felt to the present day. Post World War II, the development of military aviation was spurred by the Cold War stand-off between the super-powers. The helicopter appeared late in World War II and matured into an indispensable part of military aviation, transporting troops and providing expanded anti-submarine capabilities to smaller warships, negating

1344-789: The KC-135, KC-46, KC-767, A310 MRTT, and the KC-130J. These aircraft are a part of many countries' militant assets. Training aircraft are used to train recruits to fly aircraft and to provide additional training for specialized roles such as in air combat. Transport aircraft transport troops and supplies. Cargo can be on pallets for quick unloading. Cargo, and personnel may also be discharged from flying aircraft on parachutes . Also included in this category are aerial tankers, which can refuel other aircraft while in flight . Helicopters and gliders can transport troops and supplies to areas where other aircraft would be unable to land. An air force

1400-506: The above solutions. A well-known example is the Rozière balloon which combines a core of helium with an outer shell of hot air. The gaseous state of water is lighter than air (density 0.804 g/L at STP, average molecular mass 18.015 g/mol) due to water's low molar mass when compared with typical atmospheric gases such as nitrogen gas (N 2 ). It is non-flammable and much cheaper than helium. The concept of using steam for lifting

1456-413: The advantage that it is inert and abundantly available, because it is the major component of air. However, because nitrogen is only 3% lighter than air, it is not a good choice for a lifting gas. Ethylene is an unsaturated hydrocarbon that's 3% less dense than air. Unlike nitrogen however, ethylene is highly flammable and far more expensive, rendering use as a lifting gas highly impractical. Diborane

1512-529: The air contained within. In 2021, a group of researchers successfully levitated a series of carbon aerogels by heating them with a halogen lamp, which had the effect of lowering the density of the air trapped in the porous microstructure of the aerogel, allowing the aerogel to float. Hydrogen and helium are the most commonly used lift gases. Although helium is twice as heavy as (diatomic) hydrogen, they are both significantly lighter than air. The lifting power in air of hydrogen and helium can be calculated using

1568-437: The amount of mass that can be lifted by hydrogen in air at sea level, equal to the density difference between hydrogen and air, is: and the buoyant force for one m of hydrogen in air at sea level is: Therefore, the amount of mass that can be lifted by helium in air at sea level is: and the buoyant force for one m of helium in air at sea level is: Thus hydrogen's additional buoyancy compared to helium is: This calculation

1624-534: The ascent or the balloon is strong enough to withstand the change in pressure. Divers use lifting bags (upside down bags) that they fill with air to lift heavy items like cannons and even whole ships during underwater archaeology and shipwreck salvaging . The air is either supplied from diving cylinders or pumped through a hose from the diver's ship on the surface. Submarines use ballast tanks and trim tanks with air to regulate their buoyancy , essentially making them underwater " airships ". Bathyscaphes are

1680-443: The balloon is also lower. This means that while the mass of lifting gas and mass of displaced air for a given lift are the same as at lower altitude, the volume of the balloon is much greater at higher altitudes. A balloon that is designed to lift to extreme heights ( stratosphere ), must be able to expand enormously in order to displace the required amount of air. That is why such balloons seem almost empty at launch, as can be seen in

1736-552: The building of new carriers. During World War II, U-boats threatened the ability of the Allies to transport troops and war materiel to Europe, spurring the development of very long range Maritime patrol aircraft, whose capability of independently detecting and destroying submerged submarines was greatly increased with new detection systems, including sonobuoys , Leigh Lights , and radar , along with better weapons including homing torpedoes and improved depth charges . This played

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1792-525: The capabilities of both a fighter or a bomber, depending on what the mission calls for. Reconnaissance aircraft and scout helicopters are primarily used to gather intelligence. They are equipped with photographic, infrared, radar, and television sensors. This role is increasingly being filled by spy satellites and unmanned aerial vehicles . Refueling aircraft are used to refuel fighters and reconnaissance aircraft, extending mission reach and flying range. These aircraft include but are not limited to

1848-471: The compact suite of electronics it is today. The advancement in sonobuoy technology aided the development of aircraft such as the P-2 Neptune , S-2 Tracker , S-3B Viking and P-3 Orion for anti-submarine warfare. Sonobuoys are classified into three categories: active, passive and special purpose. This information is analyzed by computers, acoustic operators and tactical coordinators to interpret

1904-532: The diving depth of submarines of the era was so limited. If contact was made, they would follow the submarine while summoning surface ships by radio to attack it. Sonar saw extremely limited use and was mostly tested in the Atlantic Ocean with few naval officers seeing any merit in the system. With the end of World War I came the end to serious development of sonar in the United States, a fact that

1960-470: The early 1960s, missiles were expected to replace manned interceptors and the guns in other manned aircraft. They failed to live up to expectations as surface-to-air missiles lacked flexibility and were not as effective as manned interceptors, and fighters equipped only with air-to-air missiles had limited effectiveness against opposing aircraft which could avoid being hit. Missiles were also expensive, especially against low-value ground targets. The 1970s saw

2016-589: The end of World War I , military aviation had rapidly embraced many specialized roles, such as artillery spotting, air superiority, bombing, ground attack, and anti-submarine patrols. Technological improvements were made at a frenzied pace, and the first all-metal cantilevered airplanes were going into service as the war ended. Between the major world wars incremental improvements made in many areas, especially powerplants, aerodynamics, structures, and weapons, led to an even more rapid advance in aircraft technology during World War II, with large performance increases and

2072-513: The first strategic bomber units, however, they wouldn't be tested until the Spanish Civil War where the perceived effects of mass bombardment would encourage their widespread use during World War II. Carrier aviation also first appeared during World War I, and likewise came to play a major role during World War II, with most major navies recognizing the aircraft carrier's advantages over the battleship and devoting massive resources to

2128-555: The introduction of aircraft into new roles, including Airborne Early Warning , electronic warfare , weather reconnaissance , and flying lifeboats. Great Britain used aircraft to suppress revolts throughout the Empire during the interwar period and introduced the first military transports , which revolutionized logistics , allowing troops and supplies to be quickly delivered over vastly greater distances. While they first appeared during World War I, ground attack aircraft didn't provide

2184-620: The large proportion of air within the solid and not the silicon construction materials. Taking advantage of this, SEAgel , in the same family as aerogel but made from agar , can be filled with helium gas to create a solid which floats when placed in an open top container filled with a dense gas. Sonobuoy A sonobuoy (a portmanteau of sonar and buoy ) is a small expendable sonar buoy dropped from aircraft or ships for anti-submarine warfare or underwater acoustic research. Sonobuoys are typically around 13 cm (5 in) in diameter and 91 cm (3 ft) long. When floating on

2240-415: The lightest existing gas (7% the density of air, 0.08988 g/L at STP), seems to be the most appropriate gas for lifting. It can be easily produced in large quantities, for example with the water-gas shift reaction or electrolysis , but hydrogen has several disadvantages: Helium is the second lightest gas (0.1786 g/L at STP). For that reason, it is an attractive gas for lifting as well. A major advantage

2296-773: The need for large numbers of small carriers. The need to out-perform opponents pushed new technology and aircraft developments in the U.S.S.R. and the United States , among others, and the Korean War and the Vietnam War tested the resulting designs. Incredible advances in electronics were made, starting with the first electronic computers during World War II and steadily expanding from its original role of cryptography into communications, data processing, reconnaissance, remotely piloted aircraft, and many other roles until it has become an integral aspect of modern warfare. In

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2352-409: The new buoys in service beginning in July 1936. These buoys weighed 700 pounds (320 kg), could be deployed or recovered by Coast and Geodetic Survey ships in five minutes, and were equipped with subsurface hydrophones, batteries, and radio transmitters that automatically sent a radio signal when their hydrophones detected the sound of a ranging explosion. These "radio-sonobuoys" were the ancestors of

2408-406: The photo. A different approach for high altitude ballooning, especially used for long duration flights is the superpressure balloon . A superpressure balloon maintains a higher pressure inside the balloon than the external (ambient) pressure. Because of the enormous density difference between water and gases (water is about 1,000 times denser than most gases), the lifting power of underwater gases

2464-442: The return of the gun-armed fighter, and a greater emphasis on maneuverability. The 1980s through to the present day were characterized by stealth technology and other countermeasures. Today, a country's military aviation forces are often the first line of defense against an attack, or the first forces to attack the enemy, and effective military aviation forces (or lack thereof) have proved decisive in several recent conflicts such as

2520-588: The severe limitations of early aircraft. The U.S. Army Signal Corps purchased a Wright Model A on 2 August 1909 which became the first military aircraft in history. In 1911, the Italians used a variety of aircraft types in reconnaissance, photo-reconnaissance, and bombing roles during the Italo-Turkish War . On October 23, 1911, an Italian pilot, Captain Carlo Piazza, flew over Turkish lines on

2576-404: The smaller molecules of hydrogen and helium. Many lighter-than-air balloons are made of aluminized plastic that limits such leakage; hydrogen and helium leak rapidly through latex balloons. However, methane is highly flammable and like hydrogen is not appropriate for use in passenger-carrying airships. It is also relatively dense and a potent greenhouse gas . It is also possible to combine some of

2632-401: The sonobuoy information. Active and/or passive sonobuoys may be laid in large fields or barriers for initial detection. Active buoys may then be used for precise location. Passive buoys may also be deployed on the surface in patterns to allow relatively precise location by triangulation . Multiple aircraft or ships monitor the pattern either passively listening or actively transmitting to drive

2688-533: The sonobuoys that began to appear in the 1940s. The damage inflicted upon the Allies by German U-boats during World War II made the need for sonar a priority. With millions of tons of shipping being sunk in the Atlantic, there was a need to locate submarines so that they could be sunk or prevented from attacking. Sonar was installed on a number of ships along with radar and high-frequency direction finding ("Huff-Duff") to detect surfaced submarines. While sonar

2744-1008: The test ranges where they are flown. Fighters establish and maintain air superiority . Speed and maneuverability are usually requirements and they carry a variety of weapons, including machine guns and guided missiles, to do this. Forward Air Control directs close air support aircraft to ensure that the intended targets are nullified and friendly troops remain uninjured. Ground-attack aircraft support ground troops by weakening or nullifying enemy defenses. Helicopter gunships and specialized ground attack aircraft attack enemy armor or troops and provide close air support for ground troops. Liaison aircraft are usually small, unarmed aircraft used to deliver messages and key personnel. Maritime Patrol Aircraft are used to control sea-lanes, and are often equipped with special electronic gear for detecting and sinking submarines, such as sonar. They are also used for search and rescue missions and fisheries patrols. Multirole combat aircraft combine

2800-435: The theory of buoyancy as follows: Thus helium is almost twice as dense as hydrogen. However, buoyancy depends upon the difference of the densities (ρ gas ) − (ρ air ) rather than upon their ratios. Thus the difference in buoyancies is about 8%, as seen from the buoyancy equation: Where F B = Buoyant force (in newton ); g = gravitational acceleration = 9.8066 m/s = 9.8066 N/kg; V = volume (in m ). Therefore,

2856-443: The use of human ears to discriminate man-made noises from the oceanic background. However, they demonstrated that the technology was viable. With the development of better hydrophones, the transistor and miniaturization, and the realization that very low frequency sound was important, more effective acoustic sensors followed. The sonobuoy went from being an imposing six-foot (1.8 m) tall, two-foot (0.61 m) diameter sensor to

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2912-460: The waning days of World War I . At the time the only way to detect submarines was by listening for them (passive sonar), or visually by chance when they were on the surface recharging their battery banks. Air patrols (the British mostly used small airships which had the advantage of long endurance) could spot surfaced submarines and occasionally, when conditions were right, even submerged ones as

2968-420: The water, sonobuoys have both a radio transmitter above the surface and hydrophone sensors underwater. Sonobuoys are ejected from aircraft in canisters and deploy upon water impact. An inflatable surface float with a radio transmitter remains on the surface for communication with the aircraft, while one or more hydrophone sensors and stabilizing equipment descend below the surface to a selected depth that

3024-465: The world's first aerial reconnaissance mission, and on November 1, the first ever aerial bomb was dropped by Sottotenente Giulio Gavotti , on Turkish troops in Libya , from an early model of Etrich Taube aircraft. The Turks , lacking anti-aircraft weapons, were the first to shoot down an airplane by rifle fire. The earliest military role filled by aircraft was reconnaissance , however, by

3080-485: Was a primitive system, it was constantly improved. Modern anti-submarine warfare methods evolved from the techniques devised for the movement of convoys and battle groups through hostile waters during World War II. It was imperative that submarines be detected and neutralized long before the task group came within range of an attack. Aircraft-based submarine detection was the obvious solution. The maturity of radio communication and sonar technology made it possible to combine

3136-611: Was to be fatal in the early days of World War II . However, considerable development of ASDIC took place in the United Kingdom, including integration with a plotting table and weapon. While the United Kingdom pursued the development of sonar during the interwar period, the United States Coast and Geodetic Survey during the 1920s developed the radio acoustic ranging method of fixing the position of survey ships during hydrographic survey operations by detonating

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