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96-424: The Pratt & Whitney R-2800 Double Wasp is an American twin-row, 18-cylinder, air-cooled radial aircraft engine with a displacement of 2,800 cu in (46 L), and is part of the long-lived Wasp family of engines . The R-2800 saw widespread use in many important American aircraft during and after World War II . During the war years, Pratt & Whitney continued to develop new ideas to upgrade

192-508: A Joint Security Area at Panmunjom . The conflict caused more than 1 million military deaths and an estimated 2 to 3 million civilian deaths, a larger proportion of civilian deaths than in World War II or the Vietnam War . Alleged war crimes include the mass killing of suspected communists by Seoul and the torture and starvation of prisoners of war by Pyongyang. North Korea became one of

288-412: A closed circuit carrying liquid coolant through channels in the engine block and cylinder head. A fluid in these channels absorbs heat and then flows to a heat exchanger or radiator where the coolant releases heat into the air (or raw water , in the case of marine engines ). Thus, while they are not ultimately cooled by the liquid, as the heat is exchanged with some other fluid like air, because of

384-430: A fluid is a function of its capacity and the difference in input and output temperatures. As the boiling point of water is reduced with lower pressure, and the water could not be efficiently pumped as steam, radiators had to have enough cooling power to account for the loss in cooling power as the aircraft climbed. The resulting radiators were quite large and caused a significant amount of aerodynamic drag . This placed

480-557: A future independent state. Due to political disagreements and influence from their backers, the zones formed their own governments in 1948. The DPRK was led by Kim Il Sung in Pyongyang , and the ROK by Syngman Rhee in Seoul ; both claimed to be the sole legitimate government of all of Korea and engaged in border clashes as internal unrest was fomented by communist groups in the south. On 25 June 1950,

576-501: A general attack across the 38th parallel, rather than a limited operation in Ongjin. Kim was concerned that South Korean agents had learned about the plans and that South Korean forces were strengthening their defenses. Stalin agreed to this change. While these preparations were underway in the North, there were clashes along the 38th parallel, especially at Kaesong and Ongjin, many initiated by

672-486: A great percentage of the heat generated, around 44%, escapes through the exhaust. Another 8% or so ends up in the oil , which itself has to be cooled in an oil cooler . This means less than half of the heat has to be removed through other systems. In an air-cooled engine, only about 12% of the heat flows out through the metal fins. Air cooled engines usually run noisier, however it provides more simplicity which gives benefits when it comes to servicing and part replacement and

768-440: A horizontal fashion as a Flat engine , while vertical Straight-four engine have been used. Examples of past air-cooled road vehicles, in roughly chronological order, include: During the 1920s and 30s there was a great debate in the aviation industry about the merits of air-cooled vs. liquid-cooled designs. At the beginning of this period, the liquid used for cooling was water at ambient pressure. The amount of heat carried away by

864-451: A mixture of water and methanol into the carburetor to increase power for short periods. Several models of the R-2800s were fitted with ADI as standard equipment and were not given the W suffix. Few commercial aircraft used water injection. "A" Series: "B" Series: "C" Series "D" Series: "E" Series: The following is a partial list of aircraft that were powered by

960-579: A national political constitution on 17 July and elected Syngman Rhee as president on 20 July. The Republic of Korea (South Korea) was established on 15 August 1948. In the Soviet-Korean Zone of Occupation, the Soviets agreed to the establishment of a communist government led by Kim Il Sung. The 1948 North Korean parliamentary elections took place in August. The Soviet Union withdrew its forces in 1948 and

1056-598: A telegram. Mao accepted the decision made by Kim and Stalin to unify Korea but cautioned Kim over possible US intervention. Soviet generals with extensive combat experience from World War II were sent to North Korea as the Soviet Advisory Group. They completed plans for attack by May and called for a skirmish to be initiated in the Ongjin Peninsula on the west coast of Korea. The North Koreans would then launch an attack to capture Seoul and encircle and destroy

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1152-544: Is a list of representative R-2800 variants, describing some of the mechanical changes made during development of the Double Wasp. Power ratings quoted are usually maximum "military" power that the engine could generate on takeoff and at altitude; 100 Octane fuel was used, unless otherwise noted. The R-2800 was developed and modified into a basic sequence of subtypes, "A" through "E" series, each of which indicated major internal and external modifications and improvements, such that

1248-512: Is overrun by unprovoked armed attack would start a disastrous chain of events leading most probably to world war." While there was hesitance by some in the US government to get involved, considerations about Japan fed into the decision to engage on behalf of South Korea. After the fall of China to the communists, US experts saw Japan as the region's counterweight to the Soviet Union and China. While there

1344-418: Is usually cheaper to be maintained. Many motorcycles use air cooling for the sake of reducing weight and complexity. Few current production automobiles have air-cooled engines (such as Tatra 815 ), but historically it was common for many high-volume vehicles. The orientation of the engine cylinders is commonly found in either single-cylinder or coupled in groups of two, and cylinders are commonly oriented in

1440-470: The Cold War between the Soviet Union and US. Fighting ended in 1953 with an armistice but no peace treaty , leading to the ongoing Korean conflict characterized by phases of diplomacy and confrontation. After the end of World War II in 1945, Korea, which had been a Japanese colony for 35 years, was divided by the Soviet Union and the US into two occupation zones at the 38th parallel , with plans for

1536-526: The Korean People's Army (KPA), equipped and trained by the Soviets, launched an invasion of the south. In the absence of the Soviet Union's representative, the UN Security Council denounced the attack and recommended member states to repel the invasion. UN forces comprised 21 countries, with the US providing around 90% of military personnel. Seoul was captured on 28 June, and by early August,

1632-660: The Republic of Korea Army (ROKA) and its allies were nearly defeated, holding onto only the Pusan Perimeter in the peninsula's southeast. On 15 September, UN forces landed at Inchon near Seoul, cutting off KPA troops and supply lines. UN forces broke out from the perimeter on 18 September, re-captured Seoul, and invaded North Korea in October, capturing Pyongyang and advancing towards the Yalu River —the border with China. On 19 October,

1728-654: The atomic bombing of Hiroshima . By 10 August, the Red Army had begun to occupy the north of Korea. On 10 August in Washington , US Colonels Dean Rusk and Charles H. Bonesteel III were assigned to divide Korea into Soviet and US occupation zones and proposed the 38th parallel as the dividing line. This was incorporated into the US General Order No. 1 , which responded to the Japanese surrender on 15 August. Explaining

1824-438: The "E" series engines had very few parts in common with the "A".. Pratt & Whitney's internal variant identification incorporated the series letter as part of the designation, for example Double Wasp S1A4-G ("A" series) and Double Wasp CB17 ("C" series). Data from White (Airlife) unless otherwise noted: The dash number for each military type (e.g.: -21 ) was allocated to identify the complete engine model in accordance with

1920-709: The 1900s. The first commercial production was by the New Way Motor Company of Lansing, Michigan, US. The company produced air-cooled engines in single and twin cylinders in both horizontal and vertical cylinder format. Subsequent to their initial production which was exported worldwide, other companies took up the advantages of this cooling method, especially in small portable engines. Applications include mowers, generators, outboard motors, pump sets, saw benches and auxiliary power plants and more. Korean War Korean Demilitarized Zone established Together: 1,742,000 The Korean War (25 June 1950 – 27 July 1953)

2016-639: The 38th parallel and establishing English as the official language during military control. On 8 September, US Lieutenant General John R. Hodge arrived in Incheon to accept the Japanese surrender south of the 38th parallel. Appointed as military governor, Hodge directly controlled South Korea as head of the United States Army Military Government in Korea (USAMGIK 1945–48). In December 1945, Korea

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2112-515: The 38th parallel. Armistice negotiations began in July 1951, but dragged on as the fighting became a war of attrition and the north suffered heavy damage from U.S. bombing . Combat ended on 27 July 1953 with the signing of the Korean Armistice Agreement , which allowed the exchange of prisoners and created a 4-kilometre (2.5 mi) wide Demilitarized Zone (DMZ) along the frontline, with

2208-670: The Chinese People's Volunteer Army (PVA) crossed the Yalu and entered the war on the side of the north. UN forces retreated from North Korea in December, following the PVA's first and second offensive . Communist forces captured Seoul again in January 1951 before losing it to a UN counter-offensive two months later. After an abortive Chinese spring offensive , UN forces retook territory roughly up to

2304-687: The Chinese Civil War, while US forces remained stationed in South Korea. By spring 1950, he believed that the strategic situation had changed: PLA forces under Mao Zedong had secured final victory, US forces had withdrawn from Korea, and the Soviets had detonated their first nuclear bomb , breaking the US monopoly. As the US had not directly intervened to stop the communists in China, Stalin calculated they would be even less willing to fight in Korea, which had less strategic significance. The Soviets had cracked

2400-687: The Chinese PLA during the war. North Korea also provided the Chinese Communists in Manchuria with a safe refuge for non-combatants and communications with the rest of China. The North Korean contributions to the Chinese Communist victory were not forgotten after the creation of the People's Republic of China (PRC) in 1949. As a token of gratitude, between 50,000 and 70,000 Korean veterans who served in

2496-778: The Corsair's naval rival, the Grumman F6F Hellcat , the US Army Air Forces' Republic P-47 Thunderbolt (which unusually, for single-engined aircraft, used a General Electric turbocharger ), the twin-engine Martin B-26 Marauder and Douglas A-26 Invader , as well as the first purpose-built twin-engine radar-equipped night fighter, the Northrop P-61 Black Widow . When the US entered the war in December 1941, designs advanced rapidly, and long-established engines such as

2592-468: The Double Wasp served with other countries well past the Korean War, some being retired as late as the latter part of the 1960s when the aircraft were replaced. Engines grow in power with development, but a major war demands the utmost performance from engines fitted to aircraft whose life in front-line service was unlikely to exceed 50 hours flying, over a period of only a month or two. In peacetime however,

2688-466: The Double Wasp was introduced with a smaller incremental power increase than was typical of earlier engines. Nevertheless, in 1941 the power output of production models increased to 2,100 hp (1,600 kW), and to 2,400 hp (1,800 kW) late in the war. Even more was coaxed from experimental models, with fan-cooled subtypes like the R-2800-57 producing 2,800 hp (2,100 kW), but in general

2784-585: The Duplex-Cyclone. The Double Wasp was more powerful than the world's only other modern 18-cylinder engine, the Gnome-Rhône 18L of 3,442 cu in (56.40 L). The Double Wasp was much smaller in displacement than either of the other 18-cylinder designs, and heat dissipation was a greater problem. To enable more efficient cooling, the usual practice of casting or forging the cylinder head cooling fins that had been effective enough for other engine designs

2880-677: The Light-Sport Aircraft ( LSA ) and ultralight aircraft market. Rotax uses a combination of air-cooled cylinders and liquid-cooled cylinder heads. Some small diesel engines, e.g. those made by Deutz AG and Lister Petter are air-cooled. Probably the only big Euro 5 truck air-cooled engine (V8 320 kW power 2100 N·m torque one) is being produced by Tatra . BOMAG part of the FAYAT group also utilizes an air cooled inline 6 cylinder motor, in many of their construction vehicles. Stationary or portable engines were commercially introduced early in

2976-565: The Navy underwriting air-cooled engine development at Pratt & Whitney and Wright Aeronautical . Most other groups, especially in Europe where aircraft performance was rapidly improving, were more concerned with the issue of drag. While air-cooled designs were common on light aircraft and trainers, as well as some transport aircraft and bombers , liquid-cooled designs remained much more common for fighters and high-performance bombers. The drag issue

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3072-474: The North. On 28 June, Rhee ordered the massacre of suspected political opponents in his own country. In five days, the ROK, which had 95,000 troops on 25 June, was down to less than 22,000 troops. In early July, when US forces arrived, what was left of the ROK was placed under US operational command of the United Nations Command . The Truman administration was unprepared for the invasion. Korea

3168-622: The PLA were sent back along with their weapons, and they later played a significant role in the initial invasion of South Korea. China promised to support the North Koreans in the event of a war against South Korea. By 1948, a North Korea-backed insurgency had broken out in the southern half of the peninsula. This was exacerbated by the undeclared border war between the Koreas, which saw division-level engagements and thousands of deaths on both sides. The ROK

3264-783: The R-2800 (and a few prototypes that utilized it at one point): Data from FAA TCDS Related development Comparable engines Related lists Air-cooled Air-cooled engines are widely seen in applications where weight or simplicity is the primary goal. Their simplicity makes them suited for uses in small applications like chainsaws and lawn mowers , as well as small generators and similar roles. These qualities also make them highly suitable for aviation use, where they are widely used in general aviation aircraft and as auxiliary power units on larger aircraft. Their simplicity, in particular, also makes them common on motorcycles . Most modern internal combustion engines are cooled by

3360-629: The R-2800 was a rather highly developed powerplant right from the beginning. The R-2800 powered several types of fighters and medium bombers during the war, including the US Navy's Vought F4U Corsair , with the XF4U-1 first prototype Corsair becoming the first airframe to fly (as originally designed) with the Double Wasp in its XR-2800-4 prototype version on May 29, 1940, and the first single-engine American fighter plane to exceed 400 mph (640 km/h) in level flight during October 1940. The R-2800 also powered

3456-547: The ROK had 98,000 soldiers (65,000 combat, 33,000 support), no tanks (they had been requested from the U.S. military, but requests were denied), and a 22-plane air force comprising 12 liaison-type and 10 AT-6 advanced-trainer airplanes. Large U.S. garrisons and air forces were in Japan, but only 200–300 U.S. troops were in Korea. At dawn on 25 June 1950, the KPA crossed the 38th parallel behind artillery fire. It justified its assault with

3552-524: The ROK. The final stage would involve destroying South Korean government remnants and capturing the rest of South Korea, including the ports. On 7 June 1950, Kim called for a Korea-wide election on 5–8 August 1950 and a consultative conference in Haeju on 15–17 June. On 11 June, the North sent three diplomats to the South as a peace overture, which Rhee rejected outright. On 21 June, Kim revised his war plan to involve

3648-519: The ROKA launched a three-pronged assault on the insurgents in South Cholla and Taegu . By March 1950, the ROKA claimed 5,621 guerrillas killed or captured and 1,066 small arms seized. This operation crippled the insurgency. Soon after, North Korea made final attempts to keep the uprising active, sending battalion-sized units of infiltrators under the commands of Kim Sang-ho and Kim Moo-hyon. The first battalion

3744-481: The South Korean interior intensified; persistent operations, paired with worsening weather, denied the guerrillas sanctuary and wore away their fighting strength. North Korea responded by sending more troops to link up with insurgents and build more partisan cadres; North Korean infiltrators had reached 3,000 soldiers in 12 units by the start of 1950, but all were destroyed or scattered by the ROKA. On 1 October 1949,

3840-470: The South from 5,000 to 1,000. However, Kim Il Sung believed widespread uprisings had weakened the South Korean military and that a North Korean invasion would be welcomed by much of the South Korean population. Kim began seeking Stalin's support for an invasion in March 1949, traveling to Moscow to persuade him. Stalin initially did not think the time was right for a war in Korea. PLA forces were still embroiled in

3936-435: The South, armed by the U.S. military with mostly small arms, but no heavy weaponry. Several generals, such as Lee Kwon-mu , were PLA veterans born to ethnic Koreans in China. While older histories of the conflict often referred to these ethnic Korean PLA veterans as being sent from northern Korea to fight in the Chinese Civil War before being sent back, recent Chinese archival sources studied by Kim Donggill indicate that this

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4032-693: The South. The ROK was being trained by the US Korean Military Advisory Group (KMAG). On the eve of the war, KMAG commander General William Lynn Roberts voiced utmost confidence in the ROK and boasted that any North Korean invasion would merely provide "target practice". For his part, Syngman Rhee repeatedly expressed his desire to conquer the North, including when US diplomat John Foster Dulles visited Korea on 18 June. Though some South Korean and US intelligence officers predicted an attack, similar predictions had been made before and nothing had happened. The Central Intelligence Agency noted

4128-720: The Soviet Union would not move against US forces in Korea. The Truman administration believed it could intervene in Korea without undermining its commitments elsewhere. On 25 June 1950, the United Nations Security Council unanimously condemned the North Korean invasion of South Korea with Resolution 82 . The Soviet Union, a veto-wielding power , had boycotted Council meetings since January 1950, protesting Taiwan 's occupation of China's permanent seat . The Security Council, on 27 June 1950, published Resolution 83 recommending member states provide military assistance to

4224-741: The UK, and the US decided that "in due course, Korea shall become free and independent". At the Tehran Conference in 1943 and the Yalta Conference in February 1945, the Soviet Union promised to join its allies in the Pacific War within three months of the victory in Europe . Germany officially surrendered on 8 May 1945, and the USSR declared war on Japan and invaded Manchuria on 8 August 1945, two days after

4320-450: The US Navy used even (e.g.: -8). After 1940, however, in the interests of standardization, engines were sometimes built to a joint Army-Navy contract, in which case the engines used a common numeric suffix (e.g. the -10 was used by both Army and Navy aircraft.) The suffix W e.g.: -10W denotes a sub-series modified to use water injection . The "Anti-Detonant Injection" (ADI) system injected

4416-657: The US in 1949. With the end of the war with Japan , the Chinese Civil War resumed in earnest between the Communists and the Nationalist -led government. While the Communists were struggling for supremacy in Manchuria, they were supported by the North Korean government with matériel and manpower. According to Chinese sources, the North Koreans donated 2,000 railway cars worth of supplies while thousands of Koreans served in

4512-615: The USAMGIK declared martial law . Citing the inability of the Joint Commission to make progress, the US government decided to hold an election under UN auspices to create an independent Korea. The Soviet authorities and Korean communists refused to cooperate on the grounds it would not be fair, and many South Korean politicians boycotted it. The 1948 South Korean general election was held in May. The resultant South Korean government promulgated

4608-538: The Wright Cyclone and Double Wasp were re-rated on fuel of much higher octane rating ( anti-knock value) to give considerably more power. By 1944, versions of the R-2800 powering late-model P-47s (and other aircraft) had a rating (experimental) of 2,800 hp (2,100 kW) on 115-grade fuel with water injection. After World War II, the engine was used in the Korean War , and surplus World War II aircraft powered by

4704-420: The area to that end. The Truman administration still refrained from committing troops on the ground, because advisers believed the North Koreans could be stopped by air and naval power alone. The Truman administration was uncertain whether the attack was a ploy by the Soviet Union, or just a test of US resolve. The decision to commit ground troops became viable when a communiqué was received on 27 June indicating

4800-479: The area". As Rusk's comments indicate, the US doubted whether the Soviets would agree. Joseph Stalin , however, maintained his wartime policy of cooperation, and on 16 August, the Red Army halted at the 38th parallel for three weeks to await the arrival of US forces. On 7 September 1945, General Douglas MacArthur issued Proclamation No. 1 to the people of Korea, announcing US military control over Korea south of

4896-470: The border, starting in May 1949. Border clashes between South and North continued on 4 August 1949, when thousands of North Korean troops attacked South Korean troops occupying territory north of the 38th parallel. The 2nd and 18th ROK Infantry Regiments repulsed attacks in Kuksa-bong, and KPA troops were "completely routed". Border incidents decreased by the start of 1950. Meanwhile, counterinsurgencies in

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4992-674: The border, these guerrillas launched an offensive in September aimed at undermining the South Korean government and preparing the country for the KPA's arrival in force. This offensive failed. However, the guerrillas were now entrenched in the Taebaek-san region of the North Gyeongsang Province and the border areas of the Gangwon Province . While the insurgency was ongoing, the ROKA and KPA engaged in battalion-sized battles along

5088-417: The call was for reliability over a period of perhaps a dozen years, and the R-2800's reliability commended its use for long-range patrol aircraft and for the Douglas DC-6 , Martin 4-0-4 , and Convair 240 transports. The last two were twin-engine aircraft of size, passenger capacity, and high wing loading comparable to the DC-4 - itself usually powered by the R-2000 bored-out version of the Twin Wasp - and

5184-487: The choice of the 38th parallel, Rusk observed, "Even though it was further north than could be realistically reached by U. S. [ sic ] forces in the event of Soviet disagreement ... we felt it important to include the capital of Korea in the area of responsibility of American troops". He noted that he was "faced with the scarcity of U.S. forces immediately available and time and space factors which would make it difficult to reach very far north before Soviet troops could enter

5280-434: The claim ROK troops attacked first and that the KPA were aiming to arrest and execute the "bandit traitor Syngman Rhee". Fighting began on the strategic Ongjin Peninsula in the west. There were initial South Korean claims that the 17th Regiment had counterattacked at Haeju; some scholars argue the claimed counterattack was instead the instigating attack, and therefore that the South Koreans may have fired first. However,

5376-466: The codes used by the US to communicate with their embassy in Moscow , and reading dispatches convinced Stalin that Korea did not have the importance to the US that would warrant a nuclear confrontation. Stalin began a more aggressive strategy in Asia based on these developments, including promising economic and military aid to China through the Sino-Soviet Treaty of Friendship, Alliance and Mutual Assistance . In April 1950, Stalin permitted Kim to attack

5472-412: The communist victory in the Chinese Civil War, ethnic Korean units in the PLA were sent to North Korea. In the fall of 1949, two PLA divisions composed mainly of Korean-Chinese troops (the 164th and 166th ) entered North Korea, followed by smaller units throughout the rest of 1949. The reinforcement of the KPA with PLA veterans continued into 1950, with the 156th Division and several other units of

5568-406: The country. The Provisional Government of the Republic of Korea was founded in 1919 in Nationalist China . It failed to achieve international recognition, failed to unite the nationalist groups, and had a fractious relationship with its US-based founding president, Syngman Rhee . From 1919 to 1925 and beyond, Korean communists led internal and external warfare against the Japanese. In China,

5664-451: The defense of Italy and Greece, and the country was first on the list of the National Security Council 's post-North Korea invasion list of "chief danger spots". Truman believed if aggression went unchecked, a chain reaction would start that would marginalize the UN and encourage communist aggression elsewhere. The UN Security Council approved the use of force to help the South Koreans, and the US immediately began using air and naval forces in

5760-509: The economic and military aid promised by the Soviets. Kathryn Weathersby cites Soviet documents which said Kim secured Mao's support. Along with Mark O'Neill, she says this accelerated Kim's war preparations. Chen Jian argues Mao never seriously challenged Kim's plans and Kim had every reason to inform Stalin that he had obtained Mao's support. Citing more recent scholarship, Zhao Suisheng contends Mao did not approve of Kim's war proposal and requested verification from Stalin, who did so via

5856-415: The engine, including water injection for takeoff in cargo and passenger planes and to give emergency power in combat. First run in 1937, near the time that the larger 3,347.9 cu in (54.862 L) competing 18-cylinder Wright Duplex-Cyclone 's development had been started in May of that year, the 2,804.5 cu in (45.958 L) displacement R-2800 was first-flown by 1940, one year before

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5952-464: The first Constellations , which mostly used Wright Aeronautical's large Duplex-Cyclones. The Double Wasp still flies in restored vintage warbird aircraft displayed at air shows , and sees service worldwide on aircraft such as the Canadair CL-215 water-bomber. In addition, R-2800s continue to power Douglas DC-6 cargo and fuel-carrying aircraft in locations such as Alaska . A total of 125,334 R-2800 engines were produced between 1939 and 1960. This

6048-459: The former Fourth Field Army arriving in February; the PLA 156th Division was reorganized as the KPA 7th Division. By mid-1950, between 50,000 and 70,000 former PLA troops had entered North Korea, forming a significant part of the KPA's strength on the eve of the war's beginning. The combat veterans and equipment from China, the tanks, artillery, and aircraft supplied by the Soviets, and rigorous training increased North Korea's military superiority over

6144-472: The government and between 2,976 and 3,392 deaths. By May 1949, both uprisings had been crushed. Insurgency reignited in the spring of 1949 when attacks by guerrillas in the mountainous regions (buttressed by army defectors and North Korean agents) increased. Insurgent activity peaked in late 1949 as the ROKA engaged so-called People's Guerrilla Units. Organized and armed by the North Korean government, and backed by 2,400 KPA commandos who had infiltrated through

6240-527: The government in the South, under the condition that Mao would agree to send reinforcements if needed. For Kim, this was the fulfillment of his goal to unite Korea. Stalin made it clear Soviet forces would not openly engage in combat, to avoid a direct war with the US Kim met with Mao in May 1950 and differing historical interpretations of the meeting have been put forward. According to Barbara Barnouin and Yu Changgeng, Mao agreed to support Kim despite concerns of American intervention, as China desperately needed

6336-462: The government. At 02:00 on 28 June the ROK blew up the Hangang Bridge across the Han River in an attempt to stop the KPA. The bridge was detonated while 4,000 refugees were crossing it, and hundreds were killed. Destroying the bridge trapped many ROK units north of the river. In spite of such desperate measures, Seoul fell that same day. Some South Korean National Assemblymen remained in Seoul when it fell, and 48 subsequently pledged allegiance to

6432-454: The influence of China over Korea in the First Sino-Japanese War (1894–95), ushering in the short-lived Korean Empire . A decade later, after defeating Imperial Russia in the Russo-Japanese War , Japan made the Korean Empire its protectorate with the Eulsa Treaty in 1905, then annexed it with the Japan–Korea Treaty of 1910 . The Korean Empire fell, and Korea was directly ruled by Japan between 1910–45. Many Korean nationalists fled

6528-684: The insurgent war and border clashes. The first socialist uprising occurred without direct North Korean participation, though the guerrillas still professed support for the northern government. Beginning in April 1948 on Jeju Island , the campaign saw arrests and repression by the South Korean government in the fight against the South Korean Labor Party, resulting in 30,000 violent deaths, among them 14,373 civilians, of whom ~2,000 were killed by rebels and ~12,000 by ROK security forces. The Yeosu–Suncheon rebellion overlapped with it, as several thousand army defectors waving red flags massacred right-leaning families. This resulted in another brutal suppression by

6624-439: The invasion force, the North had 114 fighters, 78 bombers, 105 T-34-85 tanks, and some 30,000 soldiers stationed in reserve in North Korea. Although each navy consisted of only several small warships, the North and South Korean navies fought in the war as seaborne artillery for their armies. In contrast, the South Korean population was estimated at 20 million, but its army was unprepared and ill-equipped. As of 25 June 1950,

6720-401: The later C-series R-2800s with the two-piece gear reduction housings, on the "outboard" sides of the distributor casings. When the R-2800 was introduced in 1939, it was capable of producing 2,000 hp (1,500 kW), for a specific power value of 0.71 hp/cu in (32 kW/L). The design of conventional air-cooled radial engines had become so scientific and systematic by then that

6816-512: The liquid-coolant circuit they are known as liquid-cooled . In contrast, heat generated by an air-cooled engine is released directly into the air. Typically this is facilitated with metal fins covering the outside of the Cylinder Head and cylinders which increase the surface area that air can act on. Air may be force fed with the use of a fan and shroud to achieve efficient cooling with high volumes of air or simply by natural air flow with well designed and angled fins. In all combustion engines,

6912-429: The most heavily bombed countries in history, and virtually all of Korea's major cities were destroyed. No peace treaty has been signed, making the war a frozen conflict . In South Korea, the war is usually referred to as the "625 War" ( 6·25 전쟁 ; 六二五戰爭 ), the "625 Upheaval" ( 6·25 동란 ; 六二五動亂 ; yugio dongnan ), or simply "625", reflecting the date of its commencement on 25 June. In North Korea,

7008-506: The much smaller radiators and less fluid in the system, the weight and drag of these designs was well below contemporary air-cooled designs. On a weight basis, these liquid-cooled designs offered as much as 30% better performance. In the late- and post-war era, the high-performance field quickly moved to jet engines . This took away the primary market for late-model liquid-cooled engines. Those roles that remained with piston power were mostly slower designs and civilian aircraft. In these roles,

7104-541: The nationalist National Revolutionary Army and the communist People's Liberation Army (PLA) helped organize Korean refugees against the Japanese military, which had also occupied parts of China. The Nationalist-backed Koreans, led by Yi Pom-Sok , fought in the Burma campaign (1941-45). The communists, led by, among others, Kim Il Sung , fought the Japanese in Korea and Manchuria . At the Cairo Conference in 1943, China,

7200-509: The operation was conducted under the auspices of the UN. It has been sometimes referred to in the English-speaking world as "The Forgotten War" or "The Unknown War" because of the lack of public attention it received during and afterward, relative to the global scale of World War II, which preceded it, and the subsequent angst of the Vietnam War , which succeeded it. Imperial Japan diminished

7296-481: The radiator size by 50% compared to water cooled designs. The experiments were extremely successful and by 1932 the company had switched all future designs to this coolant. At the time, Union Carbide held a monopoly on the industrial process to make glycol, so it was initially used only in the US, with Allison Engines picking it up soon after. It was not until the mid-1930s that Rolls-Royce adopted it as supplies improved, converting all of their engines to glycol. With

7392-490: The report that contained the Haeju claim contained errors and outright falsehoods. KPA forces attacked all along the 38th parallel within an hour. The KPA had a combined arms force including tanks supported by heavy artillery. The ROK had no tanks, anti-tank weapons, or heavy artillery. The South Koreans committed their forces in a piecemeal fashion, and these were routed in a few days. On 27 June, Rhee evacuated Seoul with some of

7488-454: The simplicity and reduction in servicing needs is far more important than drag, and from the end of the war on almost all piston aviation engines have been air-cooled, with few exceptions. As of 2020 , most of the engines manufactured by Lycoming and Continental are used by major manufacturers of light aircraft Cirrus , Cessna and so on. Other engine manufactures using air-cooled engine technology are ULPower and Jabiru , more active in

7584-494: The southward movement by the KPA but assessed this as a "defensive measure" and concluded an invasion was "unlikely". On 23 June UN observers inspected the border and did not detect that war was imminent. Chinese involvement was extensive from the beginning, building on previous collaboration between the Chinese and Korean communists during the Chinese Civil War. Throughout 1949 and 1950, the Soviets continued arming North Korea. After

7680-532: The specification under which the engine was manufactured. Thus dash numbers did not necessarily indicate the sequence in which the engines were manufactured. For example: the -18W was a "C" series engine, built from 1945, whereas the -21 was a "B" series engine, built from 1943. Until 1940 the armed forces adhered strictly to the convention that engines built for the Army Air Forces used engine model numbers with odd numeric suffixes (e.g.: -5), while those built for

7776-458: The steam through tubes located just under the skin of the wings and fuselage, where the fast moving outside air condensed it back to water. While this concept was used on a number of record-setting aircraft in the late 1930s, it always proved impractical for production aircraft for a wide variety of reasons. In 1929, Curtiss began experiments replacing water with ethylene glycol in a Curtiss D-12 engine. Glycol could run up to 250 C and reduced

7872-427: The surface area of the fins. The twin distributors on the Double Wasp were prominently mounted on the upper surface of the forward gear reduction housing - with one of the pair of magnetos mounted between them on most models - and almost always prominently visible within a cowling, with the conduits for the spark plug wires emerging from the distributors' cases either directly forward or directly behind them, or on

7968-479: The term " Chosŏn War" ( Chinese : 朝鮮戰爭 ; pinyin : Cháoxiǎn Zhànzhēng ) is sometimes used unofficially. The term " Hán (Korean) War" ( Chinese : 韓戰 ; pinyin : Hán Zhàn ) is most used in Taiwan (Republic of China), Hong Kong and Macau . In the US, the war was initially described by President Harry S. Truman as a " police action " as the US never formally declared war on its opponents, and

8064-405: The two designs roughly equal in terms of power to drag, but the air-cooled designs were almost always lighter and simpler. In 1921, the US Navy , largely due to the efforts of Commander Bruce G. Leighton , decided that the simplicity of the air-cooled design would result in less maintenance workload, which was paramount given the limited working area of aircraft carriers . Leighton's efforts led to

8160-578: The volume of water required and the size of the radiator by as much as 30%, which opened the way to a new generation of high-powered, relatively low-drag liquid cooled inline engines such as the Rolls-Royce Merlin and Daimler-Benz DB601 , which had an advantage over the unpressurized early versions of the Jumo 211 . This also led to development work attempting to eliminate the radiator entirely using evaporative cooling , allowing it to turn to steam and running

8256-557: The war is officially referred to as the Fatherland Liberation War ( Choguk haebang chŏnjaeng ) or the " Chosŏn [Korean] War" ( 조선전쟁 ; Chosŏn chŏnjaeng ). In mainland China, the segment of the war after the intervention of the People's Volunteer Army is commonly and officially known as the "Resisting America and Assisting Korea War" ( Chinese : 抗美援朝战争 ; pinyin : Kàngměi Yuáncháo Zhànzhēng ), although

8352-547: Was administered by a US–Soviet Union Joint Commission , as agreed at the Moscow Conference , to grant independence after a five-year trusteeship. Waiting five years for independence was unpopular among Koreans, and riots broke out. To contain them, the USAMGIK banned strikes on 8 December and outlawed the PRK Revolutionary Government and People's Committees on 12 December. Following further civilian unrest,

8448-414: Was almost entirely trained and focused on counterinsurgency, rather than conventional warfare. They were equipped and advised by a force of a few hundred American officers, who were successful in helping the ROKA to subdue guerrillas and hold its own against North Korean military (Korean People's Army, KPA) forces along the 38th parallel. Approximately 8,000 South Korean soldiers and police officers died in

8544-587: Was an armed conflict on the Korean Peninsula fought between North Korea (Democratic People's Republic of Korea; DPRK) and South Korea (Republic of Korea; ROK) and their allies. North Korea was supported by the People's Republic of China and the Soviet Union , while South Korea was supported by the United Nations Command (UNC) led by the United States . The conflict was thus the first major proxy war of

8640-423: Was discarded, and instead, much thinner and closer-pitched cooling fins were machined from the solid metal of the cylinder-head forging. The fins were all cut at the same time by a gang of milling saws, automatically guided as it fed across the head in such a way that the bottom of the grooves rose and fell to make the roots of the fins follow the contour of the head, with the elaborate process substantially increasing

8736-493: Was no US policy dealing with South Korea directly as a national interest, its proximity to Japan increased its importance. Said Kim: "The recognition that the security of Japan required a non-hostile Korea led directly to President Truman's decision to intervene ... The essential point ... is that the American response to the North Korean attack stemmed from considerations of U.S. policy toward Japan." Another consideration

8832-401: Was not included in the strategic Asian Defense Perimeter outlined by United States Secretary of State Dean Acheson . Military strategists were more concerned with the security of Europe against the Soviet Union than that of East Asia . The administration was worried a war in Korea could quickly escalate without American intervention. Diplomat John Foster Dulles stated: "To sit by while Korea

8928-770: Was not the case. Rather, the soldiers were indigenous to China, as part of China's longstanding ethnic Korean community, and were recruited to the PLA in the same way as any other Chinese citizen. According to the first official census in 1949, the population of North Korea numbered 9,620,000, and by mid-1950, North Korean forces numbered between 150,000 and 200,000 troops, organized into 10 infantry divisions, one tank division, and one air force division, with 210 fighter planes and 280 tanks, who captured scheduled objectives and territory, among them Kaesong, Chuncheon , Uijeongbu , and Ongjin. Their forces included 274 T-34-85 tanks, 200 artillery pieces, 110 attack bombers, 150 Yak fighter planes, and 35 reconnaissance aircraft. In addition to

9024-498: Was reduced to a single man over the course of engagements by the ROKA 8th Division . The second was annihilated by a two-battalion hammer-and-anvil maneuver by units of the ROKA 6th Division , resulting in a toll of 584 KPA guerrillas (480 killed, 104 captured) and 69 ROKA troops killed, plus 184 wounded. By the spring of 1950, guerrilla activity had mostly subsided; the border, too, was calm. By 1949, South Korean and US military actions had reduced indigenous communist guerrillas in

9120-644: Was the Soviet reaction if the US intervened. The Truman administration was fearful a Korean war was a diversionary assault that would escalate to a general war in Europe once the US committed in Korea. At the same time, "[t]here was no suggestion from anyone that the United Nations or the United States could back away from [the conflict]". Yugoslavia —a possible Soviet target because of the Tito-Stalin split —was vital to

9216-489: Was upset by the 1929 introduction of the NACA cowl , which greatly reduced the drag of air-cooled engines in spite of their larger frontal area, and the drag related to cooling was at this point largely even. In the late 1920s into the 1930s, a number of European companies introduced cooling system that kept the water under pressure allowed it to reach much higher temperatures without boiling, carrying away more heat and thus reducing

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