The Pacific Ocean is the largest and deepest of Earth's oceanic divisions. It extends from the Arctic Ocean in the north to the Southern Ocean in the south and is bounded by Asia and Australia in the west and the Americas in the east. At 165,250,000 square kilometers in area, this largest division of the World Ocean—and, in turn, the hydrosphere—covers about 46% of Earth's water surface and about one-third of its total surface area, making it larger than all of Earth's land area combined; the centers of both the Water Hemisphere and the Western Hemisphere are in the Pacific Ocean. The equator subdivides it into the North Pacific Ocean and South Pacific Ocean, with two exceptions: the Galápagos and Gilbert Islands, while straddling the equator, are deemed wholly within the South Pacific, its mean depth is 4,000 meters. The Mariana Trench in the western North Pacific is the deepest point in the world, reaching a depth of 10,911 meters; the western Pacific has many peripheral seas. Though the peoples of Asia and Oceania have traveled the Pacific Ocean since prehistoric times, the eastern Pacific was first sighted by Europeans in the early 16th century when Spanish explorer Vasco Núñez de Balboa crossed the Isthmus of Panama in 1513 and discovered the great "southern sea" which he named Mar del Sur.
The ocean's current name was coined by Portuguese explorer Ferdinand Magellan during the Spanish circumnavigation of the world in 1521, as he encountered favorable winds on reaching the ocean. He called it Mar Pacífico, which in both Portuguese and Spanish means "peaceful sea". Important human migrations occurred in the Pacific in prehistoric times. About 3000 BC, the Austronesian peoples on the island of Taiwan mastered the art of long-distance canoe travel and spread themselves and their languages south to the Philippines and maritime Southeast Asia. Long-distance trade developed all along the coast from Mozambique to Japan. Trade, therefore knowledge, extended to the Indonesian islands but not Australia. By at least 878 when there was a significant Islamic settlement in Canton much of this trade was controlled by Arabs or Muslims. In 219 BC Xu Fu sailed out into the Pacific searching for the elixir of immortality. From 1404 to 1433 Zheng He led expeditions into the Indian Ocean; the first contact of European navigators with the western edge of the Pacific Ocean was made by the Portuguese expeditions of António de Abreu and Francisco Serrão, via the Lesser Sunda Islands, to the Maluku Islands, in 1512, with Jorge Álvares's expedition to southern China in 1513, both ordered by Afonso de Albuquerque from Malacca.
The east side of the ocean was discovered by Spanish explorer Vasco Núñez de Balboa in 1513 after his expedition crossed the Isthmus of Panama and reached a new ocean. He named it Mar del Sur because the ocean was to the south of the coast of the isthmus where he first observed the Pacific. In 1519, Portuguese explorer Ferdinand Magellan sailed the Pacific East to West on a Spanish expedition to the Spice Islands that would result in the first world circumnavigation. Magellan called the ocean Pacífico because, after sailing through the stormy seas off Cape Horn, the expedition found calm waters; the ocean was called the Sea of Magellan in his honor until the eighteenth century. Although Magellan himself died in the Philippines in 1521, Spanish Basque navigator Juan Sebastián Elcano led the remains of the expedition back to Spain across the Indian Ocean and round the Cape of Good Hope, completing the first world circumnavigation in a single expedition in 1522. Sailing around and east of the Moluccas, between 1525 and 1527, Portuguese expeditions discovered the Caroline Islands, the Aru Islands, Papua New Guinea.
In 1542–43 the Portuguese reached Japan. In 1564, five Spanish ships carrying 379 explorers crossed the ocean from Mexico led by Miguel López de Legazpi, sailed to the Philippines and Mariana Islands. For the remainder of the 16th century, Spanish influence was paramount, with ships sailing from Mexico and Peru across the Pacific Ocean to the Philippines via Guam, establishing the Spanish East Indies; the Manila galleons operated for two and a half centuries, linking Manila and Acapulco, in one of the longest trade routes in history. Spanish expeditions discovered Tuvalu, the Marquesas, the Cook Islands, the Solomon Islands, the Admiralty Islands in the South Pacific. In the quest for Terra Australis, Spanish explorations in the 17th century, such as the expedition led by the Portuguese navigator Pedro Fernandes de Queirós, discovered the Pitcairn and Vanuatu archipelagos, sailed the Torres Strait between Australia and New Guinea, named after navigator Luís Vaz de Torres. Dutch explorers, sailing around southern Africa engaged in discovery and trade.
In the 16th and 17th centuries Spain considered the Pacific Ocean a mare clausum—a sea closed to other naval powers. As the only known entrance from the Atlantic, the Strait of Magellan was at times patrolled by fleets sent to prevent entrance of non-Spanish ships. On the western side of the Pacific Ocean the Dutch threatened the Spanish Philippines; the 18th cen
Mean sea level is an average level of the surface of one or more of Earth's oceans from which heights such as elevation may be measured. MSL is a type of vertical datum – a standardised geodetic datum –, used, for example, as a chart datum in cartography and marine navigation, or, in aviation, as the standard sea level at which atmospheric pressure is measured to calibrate altitude and aircraft flight levels. A common and straightforward mean sea-level standard is the midpoint between a mean low and mean high tide at a particular location. Sea levels can be affected by many factors and are known to have varied over geological time scales; however 20th century and current millennium sea level rise is caused by global warming, careful measurement of variations in MSL can offer insights into ongoing climate change. The term above sea level refers to above mean sea level. Precise determination of a "mean sea level" is difficult to achieve because of the many factors that affect sea level. Instantaneous sea level varies quite a lot on several scales of space.
This is because the sea is in constant motion, affected by the tides, atmospheric pressure, local gravitational differences, salinity and so forth. The easiest way this may be calculated is by selecting a location and calculating the mean sea level at that point and use it as a datum. For example, a period of 19 years of hourly level observations may be averaged and used to determine the mean sea level at some measurement point. Still-water level or still-water sea level is the level of the sea with motions such as wind waves averaged out. MSL implies the SWL further averaged over a period of time such that changes due to, e.g. the tides have zero mean. Global MSL refers to a spatial average over the entire ocean. One measures the values of MSL in respect to the land. In the UK, the Ordnance Datum is the mean sea level measured at Newlyn in Cornwall between 1915 and 1921. Prior to 1921, the vertical datum was MSL at the Victoria Liverpool. Since the times of the Russian Empire, in Russia and other former its parts, now independent states, the sea level is measured from the zero level of Kronstadt Sea-Gauge.
In Hong Kong, "mPD" is a surveying term meaning "metres above Principal Datum" and refers to height of 1.230m below the average sea level. In France, the Marégraphe in Marseilles measures continuously the sea level since 1883 and offers the longest collapsed data about the sea level, it is used for main part of Africa as official sea level. As for Spain, the reference to measure heights below or above sea level is placed in Alicante. Elsewhere in Europe vertical elevation references are made to the Amsterdam Peil elevation, which dates back to the 1690s. Satellite altimeters have been making precise measurements of sea level since the launch of TOPEX/Poseidon in 1992. A joint mission of NASA and CNES, TOPEX/Poseidon was followed by Jason-1 in 2001 and the Ocean Surface Topography Mission on the Jason-2 satellite in 2008. Height above mean sea level is the elevation or altitude of an object, relative to the average sea level datum, it is used in aviation, where some heights are recorded and reported with respect to mean sea level, in the atmospheric sciences, land surveying.
An alternative is to base height measurements on an ellipsoid of the entire Earth, what systems such as GPS do. In aviation, the ellipsoid known as World Geodetic System 84 is used to define heights; the alternative is to use a geoid-based vertical datum such as NAVD88. When referring to geographic features such as mountains on a topographic map, variations in elevation are shown by contour lines; the elevation of a mountain denotes the highest point or summit and is illustrated as a small circle on a topographic map with the AMSL height shown in metres, feet or both. In the rare case that a location is below sea level, the elevation AMSL is negative. For one such case, see Amsterdam Airport Schiphol. To extend this definition far from the sea means comparing the local height of the mean sea surface with a "level" reference surface, or geodetic datum, called the geoid. In a state of rest or absence of external forces, the mean sea level would coincide with this geoid surface, being an equipotential surface of the Earth's gravitational field.
In reality, due to currents, air pressure variations and salinity variations, etc. this does not occur, not as a long-term average. The location-dependent, but persistent in time, separation between mean sea level and the geoid is referred to as ocean surface topography, it varies globally in a range of ± 2 m. Adjustments were made to sea-level measurements to take into account the effects of the 235 lunar month Metonic cycle and the 223-month eclipse cycle on the tides. Several terms are used to describe the changing relationships between sea level and dry land; when the term "relative" is used, it means change relative to a fixed point in the sediment pile. The term "eustatic" refers to global changes in sea level relative to a fixed point, such as the centre of the earth, for example as a result of melting ice-caps; the term "steric" refers to global changes in sea level due to thermal expansion and salinity variations. The term "isostatic" refers to changes in
Plutonium is a radioactive chemical element with symbol Pu and atomic number 94. It is an actinide metal of silvery-gray appearance that tarnishes when exposed to air, forms a dull coating when oxidized; the element exhibits six allotropes and four oxidation states. It reacts with carbon, nitrogen and hydrogen; when exposed to moist air, it forms oxides and hydrides that can expand the sample up to 70% in volume, which in turn flake off as a powder, pyrophoric. It can accumulate in bones, which makes the handling of plutonium dangerous. Plutonium was first produced and isolated on December 14, 1940, by a deuteron bombardment of uranium-238 in the 1.5 metre cyclotron at the University of California, Berkeley. First neptunium-238 was synthesized which subsequently beta-decayed to form this new element with atomic number 94 and atomic weight 238. Since uranium had been named after the planet Uranus and neptunium after the planet Neptune, element 94 was named after Pluto, which at the time was considered to be a planet as well.
Wartime secrecy prevented its discovery being announced until 1948. Plutonium is the element with the highest atomic number to occur in nature. Trace quantities arise in natural uranium-238 deposits when U-238 captures neutrons emitted by decay of other U-238 atoms. Plutonium is much more common on Earth since 1945 as a product of neutron capture and beta decay, where some of the neutrons released by the fission process convert uranium-238 nuclei into plutonium-239. Both plutonium-239 and plutonium-241 are fissile, meaning that they can sustain a nuclear chain reaction, leading to applications in nuclear weapons and nuclear reactors. Plutonium-240 exhibits a high rate of spontaneous fission, raising the neutron flux of any sample containing it; the presence of plutonium-240 limits a plutonium sample's usability for weapons or its quality as reactor fuel, the percentage of plutonium-240 determines its grade. Plutonium-238 has a half-life of 88 years and emits alpha particles, it is a heat source in radioisotope thermoelectric generators, which are used to power some spacecraft.
Plutonium isotopes are expensive and inconvenient to separate, so particular isotopes are manufactured in specialized reactors. Producing plutonium in useful quantities for the first time was a major part of the Manhattan Project during World War II that developed the first atomic bombs; the Fat Man bombs used in the Trinity nuclear test in July 1945, in the bombing of Nagasaki in August 1945, had plutonium cores. Human radiation experiments studying plutonium were conducted without informed consent, several criticality accidents, some lethal, occurred after the war. Disposal of plutonium waste from nuclear power plants and dismantled nuclear weapons built during the Cold War is a nuclear-proliferation and environmental concern. Other sources of plutonium in the environment are fallout from numerous above-ground nuclear tests, now banned. Plutonium, like most metals, has a bright silvery appearance at first, much like nickel, but it oxidizes quickly to a dull gray, although yellow and olive green are reported.
At room temperature plutonium is in its α form. This, the most common structural form of the element, is about as hard and brittle as gray cast iron unless it is alloyed with other metals to make it soft and ductile. Unlike most metals, it is not a good conductor of electricity, it has an unusually high boiling point. Alpha decay, the release of a high-energy helium nucleus, is the most common form of radioactive decay for plutonium. A 5 kg mass of 239Pu contains about 12.5×1024 atoms. With a half-life of 24,100 years, about 11.5×1012 of its atoms decay each second by emitting a 5.157 MeV alpha particle. This amounts to 9.68 watts of power. Heat produced by the deceleration of these alpha particles makes it warm to the touch. Resistivity is a measure of how a material opposes the flow of electric current; the resistivity of plutonium at room temperature is high for a metal, it gets higher with lower temperatures, unusual for metals. This trend continues down to 100 K, below which resistivity decreases for fresh samples.
Resistivity begins to increase with time at around 20 K due to radiation damage, with the rate dictated by the isotopic composition of the sample. Because of self-irradiation, a sample of plutonium fatigues throughout its crystal structure, meaning the ordered arrangement of its atoms becomes disrupted by radiation with time. Self-irradiation can lead to annealing which counteracts some of the fatigue effects as temperature increases above 100 K. Unlike most materials, plutonium increases in density when it melts, by 2.5%, but the liquid metal exhibits a linear decrease in density with temperature. Near the melting point, the liquid plutonium has high viscosity and surface tension compared to other metals. Plutonium has six allotropes and forms a seventh at high temperature within a limited pressure range; these allotropes, which are different structural modifications or forms of an element, have similar internal energies but varying densities and crystal structures. This makes plutonium sensitive to changes in temperature, pressure, or chemistry, allows for dramatic volume changes following phase transitions from one allotropic form to another.
The densities of the different allotropes vary from 16.00 g/cm3 to 19.86 g/cm3. The presence of these many allotropes makes machining plutonium difficult, as it changes state readily. For example, the α form exists at room temperature in unalloyed plutonium, it has machinin
The Marshall Islands the Republic of the Marshall Islands, is an island country and a United States associated state near the equator in the Pacific Ocean west of the International Date Line. Geographically, the country is part of the larger island group of Micronesia; the country's population of 53,158 people is spread out over 29 coral atolls, comprising 1,156 individual islands and islets. The islands share maritime boundaries with the Federated States of Micronesia to the west, Wake Island to the north, Kiribati to the southeast, Nauru to the south. About 27,797 of the islanders live on Majuro. Data from the United Nations indicates an estimated population in 2016 of 53,066. In 2016, 73.3% of the population were defined as being "urban". The UN indicates a population density of 295 per km2 and its projected 2020 population is 53,263. Micronesian colonists reached the Marshall Islands using canoes circa 2nd millennium BC, with interisland navigation made possible using traditional stick charts.
They settled here. Islands in the archipelago were first explored by Europeans in the 1520s, starting with Ferdinand Magellan, a Portuguese at the service of Spain, Juan Sebastián Elcano and Miguel de Saavedra. Spanish explorer Alonso de Salazar reported sighting an atoll in August 1526. Other expeditions by Spanish and English ships followed; the islands derive their name from British explorer John Marshall, who visited in 1788. The islands were known by the inhabitants as "jolet jen Anij". Spain claimed the islands in 1592, the European powers recognized its sovereignty over the islands in 1874, they had been part of the Spanish East Indies formally since 1528. Spain sold some of the islands to the German Empire in 1885, they became part of German New Guinea that year, run by the trading companies doing business in the islands the Jaluit Company. In World War I the Empire of Japan occupied the Marshall Islands, which in 1920, the League of Nations combined with other former German territories to form the South Pacific Mandate.
During World War II, the United States took control of the islands in the Gilbert and Marshall Islands campaign in 1944. Nuclear testing began in 1946 and concluded in 1958; the US government formed the Congress of Micronesia in 1965, a plan for increased self-governance of Pacific islands. The Trust Territory of the Pacific Islands in 1979 provided independence to the Marshall Islands, whose constitution and president were formally recognized by the US. Full sovereignty or Self-government was achieved in a Compact of Free Association with the United States. Marshall Islands has been a member of the Pacific Community since 1983 and a United Nations member state since 1991. Politically, the Marshall Islands is a presidential republic in free association with the United States, with the US providing defense and access to U. S.-based agencies such as the Federal Communications Commission and the United States Postal Service. With few natural resources, the islands' wealth is based on a service economy, as well as some fishing and agriculture.
The country uses the United States dollar as its currency. In 2018, it announced plans for a new cryptocurrency to be used as legal tender; the majority of the citizens of the Republic of Marshall Islands, formed in 1982, are of Marshallese descent, though there are small numbers of immigrants from the United States, China and other Pacific islands. The two official languages are Marshallese, one of the Malayo-Polynesian languages, English; the entire population of the islands practices some religion, with three-quarters of the country either following the United Church of Christ – Congregational in the Marshall Islands or the Assemblies of God. Evidence suggests that around 3,000 years ago successive waves of human migrants from Southeast Asia spread across the Western Pacific populating its many small islands; the Marshall Islands were settled by Micronesians in the 2nd millennium BC. Little is known of the islands' early history. Early settlers traveled between the islands by canoe using traditional stick charts.
The Spanish explorer Alonso de Salazar landed there in 1526, the archipelago came to be known as "Los Pintados", "Las Hermanas" and "Los Jardines" within the Spanish Empire, first falling within the jurisdiction of the Viceroyalty of New Spain, to be administered directly by Madrid upon the independence of Latin America and the dissolution of New Spain starting in 1821. They were only formally possessed by Spain for much of their colonial history, were considered part of the "Carolines", or alternatively the "Nuevas Filipinas"; the islands were left to their own affairs except for short-lived religious missions during the 16th and 17th centuries. They were ignored by European powers except for cartographic demarcation treaties between the Iberian Empires in 1529, 1750 and 1777; the archipelago corresponding to the present-day country was independently named by Krusenstern, after British explorer John Marshall, who visited them together with Thomas Gilbert in 1788, en route from Botany Bay to Canton (two s
Ivy King was the largest pure-fission nuclear bomb tested by the United States. The bomb was tested during the Truman administration as part of Operation Ivy; this series of tests involved the development of powerful nuclear weapons in response to the nuclear weapons program of the Soviet Union. The production of Ivy King was hurried to be ready in case its sister project, Ivy Mike, failed in its attempt to achieve a thermonuclear reaction; the Ivy King test took place two weeks after Mike. Unlike the Mike bomb, the Ivy King device could theoretically have been added to United States' nuclear arsenal because it was designed to be air-deliverable. On November 16, 1952 at 11:30 local time a B-36H bomber dropped the bomb over a point 2,000 feet north of Runit Island in the Enewetak atoll, resulting in a 500 kiloton explosion at 1,480 feet; the tropopause height at the time of the detonation was about 58,000 feet. The top of the King cloud reached about 74,000 feet with the mushroom base at about 40,000 feet.
The Ivy King bomb, designated as a Mk-18 bomb and named the "Super Oralloy Bomb", was a modified version of the Mk-6D bomb. Instead of using an implosion system similar to the Mk-6D, it used a 92-point implosion system developed for the Mk-13, its uranium-plutonium core was replaced by 60 kg of enriched uranium fashioned into a thin-walled sphere equivalent to four critical masses. The thin-walled sphere was a used design, which ensured that the fissile material remained sub-critical until imploded; the HEU sphere was enclosed in a natural-uranium neutron reflector. To physically prevent the HEU sphere collapsing into a critical condition if the surrounding explosives were detonated accidentally, or if the sphere was crushed following an aircraft accident, the hollow center was filled with a chain made from aluminum and boron, pulled out to arm the bomb; the boron-coated chain absorbed the neutrons needed to drive the nuclear reaction. The primary designer of the Super Oralloy Bomb, physicist Ted Taylor became a vocal proponent of nuclear disarmament.
Chuck Hansen. U. S. Nuclear Weapons: The Secret History. Arlington: AeroFax. Chuck Hansen Swords of Armageddon. Published on CD-Rom only by Chukelea, Sunnyvale, CA. Operation Ivy Video of the Ivy King Nuclear Test
The Guardian is a British daily newspaper. It was founded in 1821 as The Manchester Guardian, changed its name in 1959. Along with its sister papers The Observer and The Guardian Weekly, the Guardian is part of the Guardian Media Group, owned by the Scott Trust; the trust was created in 1936 to "secure the financial and editorial independence of the Guardian in perpetuity and to safeguard the journalistic freedom and liberal values of the Guardian free from commercial or political interference". The trust was converted into a limited company in 2008, with a constitution written so as to maintain for The Guardian the same protections as were built into the structure of the Scott Trust by its creators. Profits are reinvested in journalism rather than distributed to shareholders; the current editor is Katharine Viner: she succeeded Alan Rusbridger in 2015. Since 2018, the paper's main newsprint sections have been published in tabloid format; as of November that year, its print edition had a daily circulation of 136,834.
The newspaper has an online edition, TheGuardian.com, as well as two international websites, Guardian Australia and Guardian US. The paper's readership is on the mainstream left of British political opinion, its reputation as a platform for liberal and left-wing editorial has led to the use of the "Guardian reader" and "Guardianista" as often-pejorative epithets for those of left-leaning or "politically correct" tendencies. Frequent typographical errors in the paper led Private Eye magazine to dub it the "Grauniad" in the 1960s, a nickname still used today. In an Ipsos MORI research poll in September 2018 designed to interrogate the public's trust of specific titles online, The Guardian scored highest for digital-content news, with 84% of readers agreeing that they "trust what see in it". A December 2018 report of a poll by the Publishers Audience Measurement Company stated that the paper's print edition was found to be the most trusted in the UK in the period from October 2017 to September 2018.
It was reported to be the most-read of the UK's "quality newsbrands", including digital editions. While The Guardian's print circulation is in decline, the report indicated that news from The Guardian, including that reported online, reaches more than 23 million UK adults each month. Chief among the notable "scoops" obtained by the paper was the 2011 News International phone-hacking scandal—and in particular the hacking of the murdered English teenager Milly Dowler's phone; the investigation led to the closure of the News of the World, the UK's best-selling Sunday newspaper and one of the highest-circulation newspapers in history. In June 2013, The Guardian broke news of the secret collection by the Obama administration of Verizon telephone records, subsequently revealed the existence of the surveillance program PRISM after knowledge of it was leaked to the paper by the whistleblower and former NSA contractor Edward Snowden. In 2016, The Guardian led an investigation into the Panama Papers, exposing then-Prime Minister David Cameron's links to offshore bank accounts.
It has been named "newspaper of the year" four times at the annual British Press Awards: most in 2014, for its reporting on government surveillance. The Manchester Guardian was founded in Manchester in 1821 by cotton merchant John Edward Taylor with backing from the Little Circle, a group of non-conformist businessmen, they launched their paper after the police closure of the more radical Manchester Observer, a paper that had championed the cause of the Peterloo Massacre protesters. Taylor had been hostile to the radical reformers, writing: "They have appealed not to the reason but the passions and the suffering of their abused and credulous fellow-countrymen, from whose ill-requited industry they extort for themselves the means of a plentiful and comfortable existence, they do not toil, neither do they spin, but they live better than those that do." When the government closed down the Manchester Observer, the mill-owners' champions had the upper hand. The influential journalist Jeremiah Garnett joined Taylor during the establishment of the paper, all of the Little Circle wrote articles for the new paper.
The prospectus announcing the new publication proclaimed that it would "zealously enforce the principles of civil and religious Liberty warmly advocate the cause of Reform endeavour to assist in the diffusion of just principles of Political Economy and support, without reference to the party from which they emanate, all serviceable measures". In 1825 the paper merged with the British Volunteer and was known as The Manchester Guardian and British Volunteer until 1828; the working-class Manchester and Salford Advertiser called the Manchester Guardian "the foul prostitute and dirty parasite of the worst portion of the mill-owners". The Manchester Guardian was hostile to labour's claims. Of the 1832 Ten Hours Bill, the paper doubted whether in view of the foreign competition "the passing of a law positively enacting a gradual destruction of the cotton manufacture in this kingdom would be a much less rational procedure." The Manchester Guardian dismissed strikes as the work of outside agitators: " if an accommodation can be effected, the occupation of the agents of the Union is gone.
They live on strife "The Manchester Guardian was critical of US President Abraham Lincoln's conduct during the US Civil War, writing on the news that Abraham Lincoln had been assassinated: "Of his rule, we can never speak except as a series of acts abhorrent to every true notion of constitutional right and human liberty " C. P. Scott ma
Enewetak Atoll is a large coral atoll of 40 islands in the Pacific Ocean and with its 664 people forms a legislative district of the Ralik Chain of the Marshall Islands. With a land area total less than 5.85 square kilometres, it is no higher than 5 meters and surrounds a deep central lagoon, 80 kilometres in circumference. It is 305 kilometres west from Bikini Atoll, it was held by the Japanese from 1914 until its capture by the United States in February of 1944, during World War II. Nuclear testing by the US totaling more than 30 megatons of TNT took place during the cold war; the Runit Dome is deteriorating and could be breached by a typhoon, though the sediments in the lagoon are more radioactive than those which are contained. The U. S. government referred to the atoll as "Eniwetok" until 1974, when it changed its official spelling to "Enewetak". Enewetak Atoll formed atop a seamount; the seamount was formed in the late Cretaceous. This seamount is now about 1,400 metres below sea level, it is made of basalt, its depth is due to a general subsidence of the entire region and not because of erosion.
Enewetak has a mean elevation above sea level of 3 metres. Humans have inhabited the atoll since about 1,000 B. C; the first European visitor to Enewetak, Spanish explorer Alvaro de Saavedra, arrived on 10 October 1529. He called the island "Los Jardines". In 1794 sailors aboard the British merchant sloop Walpole called the islands "Brown's Range", it was visited by about a dozen ships before the establishment of the German colony of the Marshall Islands in 1885. With the rest of the Marshalls, Enewetak was captured by the Imperial Japanese Navy in 1914 during World War I and mandated to the Empire of Japan by the League of Nations in 1920; the Japanese administered the island under the South Pacific Mandate, but left affairs in hands of traditional local leaders until the start of World War II. The atoll, together with other part of Marshall Islands located to the west of 164°E, was placed under the governance of Pohnpei district during the Japanese administration period, is different from rest of Marshall Islands.
In November 1942, the Japanese built an airfield on Engebi Island. As they used it only for refueling planes between Truk and islands to the east, no aviation personnel were stationed there and the island had only token defenses; when the Gilberts fell to the United States, the Imperial Japanese Army assigned defense of the atoll to the 1st Amphibious Brigade, formed from the 3rd Independent Garrison, stationed in Manchukuo. The 1st Amphibious Brigade arrived on January 4, 1944; some 2,586 of its 3,940 men were left to defend Eniwetok Atoll, supplemented by aviation personnel, civilian employees, laborers. However, they were unable to finish the fortifications. During the ensuing Battle of Eniwetok, the Americans captured Enewetak in a five-day amphibious operation. Fighting took place on Engebi Islet, site of the most important Japanese installation, although some combat occurred on the main islet of Enewetak itself and on Parry Island, where there was a Japanese seaplane base. Following its capture, the anchorage at Enewetak became a major forward base for the U.
S. Navy; the daily average of ships present during the first half of July 1944 was 488. In 1950, John C. Woods, who executed the Nazi war criminals convicted at the Nuremberg Trials, was accidentally electrocuted here. After the end of World War II, Enewetak came under the control of the United States as part of the Trust Territory of the Pacific Islands until the independence of the Marshall Islands in 1986. During its tenure, the United States evacuated the local residents many times involuntarily; the atoll was used for nuclear testing as part of the Pacific Proving Grounds. Before testing commenced, the U. S. exhumed the bodies of United States servicemen killed in the Battle of Enewetak and returned them to the United States to be re-buried by their families. Forty-three nuclear tests were fired at Enewetak from 1948 to 1958; the first hydrogen bomb test, code-named Ivy Mike, occurred in late 1952 as part of Operation Ivy. This test included B-17 Flying Fortress drones to fly through the radioactive cloud to test onboard samples.
B-17 mother ships controlled the drones while flying within visual distance of them. In all 16 to 20 B-17s took part in this operation, of which half were controlling aircraft and half were drones. To examine the explosion clouds of the nuclear bombs in 1957/58 several rockets were launched. One USAF airman was lost at sea during the tests. A radiological survey of Enewetak was conducted from 1972 to 1973. In 1977, the United States military began decontamination of other islands. During the three-year, US$100 million cleanup process, the military mixed more than 80,000 cubic metres of contaminated soil and debris from the islands with Portland cement and buried it in an atomic blast crater on the northern end of the atoll's Runit Island; the material was placed in the 9.1-metre deep, 110-metre wide crater created by the May 5, 1958, "Cactus" nuclear weapons test