The Normandy landings were the landing operations on Tuesday, 6 June 1944 of the Allied invasion of Normandy in Operation Overlord during World War II. Codenamed Operation Neptune and referred to as D-Day, it was the largest seaborne invasion in history; the operation began the liberation of German-occupied France from Nazi control, laid the foundations of the Allied victory on the Western Front. Planning for the operation began in 1943. In the months leading up to the invasion, the Allies conducted a substantial military deception, codenamed Operation Bodyguard, to mislead the Germans as to the date and location of the main Allied landings; the weather on D-Day was far from the operation had to be delayed 24 hours. Adolf Hitler placed German Field Marshal Erwin Rommel in command of German forces and of developing fortifications along the Atlantic Wall in anticipation of an Allied invasion; the amphibious landings were preceded by extensive aerial and naval bombardment and an airborne assault—the landing of 24,000 US, Canadian airborne troops shortly after midnight.
Allied infantry and armoured divisions began landing on the coast of France at 06:30. The target 50-mile stretch of the Normandy coast was divided into five sectors: Utah, Gold and Sword. Strong winds blew the landing craft east of their intended positions at Utah and Omaha; the men landed under heavy fire from gun emplacements overlooking the beaches, the shore was mined and covered with obstacles such as wooden stakes, metal tripods, barbed wire, making the work of the beach-clearing teams difficult and dangerous. Casualties were heaviest at Omaha, with its high cliffs. At Gold and Sword, several fortified towns were cleared in house-to-house fighting, two major gun emplacements at Gold were disabled, using specialised tanks; the Allies failed to achieve any of their goals on the first day. Carentan, St. Lô, Bayeux remained in German hands, Caen, a major objective, was not captured until 21 July. Only two of the beaches were linked on the first day, all five beachheads were not connected until 12 June.
German casualties on D-Day have been estimated at 4,000 to 9,000 men. Allied casualties were at least 10,000, with 4,414 confirmed dead. Museums and war cemeteries in the area now host many visitors each year. After the German Army invaded the Soviet Union in June 1941, the Soviet leader Joseph Stalin began pressing his new allies for the creation of a second front in western Europe. In late May 1942 the Soviet Union and the United States made a joint announcement that a "... full understanding was reached with regard to the urgent tasks of creating a second front in Europe in 1942." However, British Prime Minister Winston Churchill persuaded US President Franklin D. Roosevelt to postpone the promised invasion as with US help, the Allies did not have adequate forces for such an activity. Instead of an immediate return to France, the western Allies staged offensives in the Mediterranean Theatre of Operations, where British troops were stationed. By mid-1943 the campaign in North Africa had been won.
The Allies launched the invasion of Sicily in July 1943, subsequently invaded the Italian mainland in September the same year. By Soviet forces were on the offensive and had won a major victory at the Battle of Stalingrad; the decision to undertake a cross-channel invasion within the next year was taken at the Trident Conference in Washington in May 1943. Initial planning was constrained by the number of available landing craft, most of which were committed in the Mediterranean and Pacific. At the Tehran Conference in November 1943, Roosevelt and Churchill promised Stalin that they would open the long-delayed second front in May 1944. Four sites were considered for the landings: Brittany, the Cotentin Peninsula and the Pas-de-Calais; as Brittany and Cotentin are peninsulas, it would have been possible for the Germans to cut off the Allied advance at a narrow isthmus, so these sites were rejected. With the Pas-de-Calais being the closest point in continental Europe to Britain, the Germans considered it to be the most initial landing zone, so it was the most fortified region.
But it offered few opportunities for expansion, as the area is bounded by numerous rivers and canals, whereas landings on a broad front in Normandy would permit simultaneous threats against the port of Cherbourg, coastal ports further west in Brittany, an overland attack towards Paris and into Germany. Normandy was hence chosen as the landing site; the most serious drawback of the Normandy coast—the lack of port facilities—would be overcome through the development of artificial Mulberry harbours. A series of specialised tanks, nicknamed Hobart's Funnies, were created to deal with conditions expected during the Normandy Campaign, such as scaling sea walls and providing close support on the beach; the Allies planned to launch the invasion on 1 May 1944. The initial draft of the plan was accepted at the Quebec Conference in August 1943. General Dwight D. Eisenhower was appointed commander of Supreme Headquarters Allied Expeditionary Force. General Bernard Montgomery was named as commander of the 21st Army Group, which comprised all of the land forces involved in the invasion.
On 31 December 1943 Eisenhower and Montgomery first saw the plan, which proposed amphibious landings by three divisions with two m
The kilogram or kilogramme is the base unit of mass in the International System of Units. Until 20 May 2019, it remains defined by a platinum alloy cylinder, the International Prototype Kilogram, manufactured in 1889, stored in Saint-Cloud, a suburb of Paris. After 20 May, it will be defined in terms of fundamental physical constants; the kilogram was defined as the mass of a litre of water. That was an inconvenient quantity to replicate, so in 1799 a platinum artefact was fashioned to define the kilogram; that artefact, the IPK, have been the standard of the unit of mass for the metric system since. In spite of best efforts to maintain it, the IPK has diverged from its replicas by 50 micrograms since their manufacture late in the 19th century; this led to efforts to develop measurement technology precise enough to allow replacing the kilogram artifact with a definition based directly on physical phenomena, now scheduled to take place in 2019. The new definition is based on invariant constants of nature, in particular the Planck constant, which will change to being defined rather than measured, thereby fixing the value of the kilogram in terms of the second and the metre, eliminating the need for the IPK.
The new definition was approved by the General Conference on Weights and Measures on 16 November 2018. The Planck constant relates a light particle's energy, hence mass, to its frequency; the new definition only became possible when instruments were devised to measure the Planck constant with sufficient accuracy based on the IPK definition of the kilogram. The gram, 1/1000 of a kilogram, was provisionally defined in 1795 as the mass of one cubic centimetre of water at the melting point of ice; the final kilogram, manufactured as a prototype in 1799 and from which the International Prototype Kilogram was derived in 1875, had a mass equal to the mass of 1 dm3 of water under atmospheric pressure and at the temperature of its maximum density, 4 °C. The kilogram is the only named SI unit with an SI prefix as part of its name; until the 2019 redefinition of SI base units, it was the last SI unit, still directly defined by an artefact rather than a fundamental physical property that could be independently reproduced in different laboratories.
Three other base units and 17 derived units in the SI system are defined in relation to the kilogram, thus its stability is important. The definitions of only eight other named SI units do not depend on the kilogram: those of temperature and frequency, angle; the IPK is used or handled. Copies of the IPK kept by national metrology laboratories around the world were compared with the IPK in 1889, 1948, 1989 to provide traceability of measurements of mass anywhere in the world back to the IPK; the International Prototype Kilogram was commissioned by the General Conference on Weights and Measures under the authority of the Metre Convention, in the custody of the International Bureau of Weights and Measures who hold it on behalf of the CGPM. After the International Prototype Kilogram had been found to vary in mass over time relative to its reproductions, the International Committee for Weights and Measures recommended in 2005 that the kilogram be redefined in terms of a fundamental constant of nature.
At its 2011 meeting, the CGPM agreed in principle that the kilogram should be redefined in terms of the Planck constant, h. The decision was deferred until 2014. CIPM has proposed revised definitions of the SI base units, for consideration at the 26th CGPM; the formal vote, which took place on 16 November 2018, approved the change, with the new definitions coming into force on 20 May 2019. The accepted redefinition defines the Planck constant as 6.62607015×10−34 kg⋅m2⋅s−1, thereby defining the kilogram in terms of the second and the metre. Since the second and metre are defined in terms of physical constants, the kilogram is defined in terms of physical constants only; the avoirdupois pound, used in both the imperial and US customary systems, is now defined in terms of the kilogram. Other traditional units of weight and mass around the world are now defined in terms of the kilogram, making the kilogram the primary standard for all units of mass on Earth; the word kilogramme or kilogram is derived from the French kilogramme, which itself was a learned coinage, prefixing the Greek stem of χίλιοι khilioi "a thousand" to gramma, a Late Latin term for "a small weight", itself from Greek γράμμα.
The word kilogramme was written into French law in 1795, in the Decree of 18 Germinal, which revised the older system of units introduced by the French National Convention in 1793, where the gravet had been defined as weight of a cubic centimetre of water, equal to 1/1000 of a grave. In the decree of 1795, the term gramme thus replaced gravet, kilogramme replaced grave; the French spelling was adopted in Great Britain when the word was used for the first time in English in 1795, with the spelling kilogram being adopted in the United States. In the United Kingdom both spellings are used, with "kilogram" having become by far the more common. UK law regulating the units to be used when trading by weight or measure does not prevent the use of either spelling. In the 19th century the French word kilo, a shortening of kilogramme, was imported into the English language where it has been used to mean both kilogram and kilometre. While kilo is acceptable in many generalist texts
Pittsburgh is a city in the Commonwealth of Pennsylvania in the United States, is the county seat of Allegheny County. As of 2018, a population of 308,144 lives within the city limits, making it the 63rd-largest city in the U. S; the metropolitan population of 2,362,453, is the largest in both the Ohio Valley and Appalachia, the second-largest in Pennsylvania, the 26th-largest in the U. S. Pittsburgh is located in the south west of the state, at the confluence of the Allegheny and Ohio rivers. Pittsburgh is known both as "the Steel City" for its more than 300 steel-related businesses and as the "City of Bridges" for its 446 bridges; the city features 30 skyscrapers, two inclined railways, a pre-revolutionary fortification and the Point State Park at the confluence of the rivers. The city developed as a vital link of the Atlantic coast and Midwest, as the mineral-rich Allegheny Mountains made the area coveted by the French and British empires, Whiskey Rebels, Civil War raiders. Aside from steel, Pittsburgh has led in manufacturing of aluminum, shipbuilding, foods, transportation, computing and electronics.
For part of the 20th century, Pittsburgh was behind only New York and Chicago in corporate headquarters employment. S. stockholders per capita. America's 1980s deindustrialization laid off area blue-collar workers and thousands of downtown white-collar workers when the longtime Pittsburgh-based world headquarters moved out; this heritage left the area with renowned museums, medical centers, research centers, a diverse cultural district. Today, Apple Inc. Bosch, Uber, Autodesk, Microsoft and IBM are among 1,600 technology firms generating $20.7 billion in annual Pittsburgh payrolls. The area has served as the long-time federal agency headquarters for cyber defense, software engineering, energy research and the nuclear navy; the area is home to 68 colleges and universities, including research and development leaders Carnegie Mellon University and the University of Pittsburgh. The nation's eighth-largest bank, eight Fortune 500 companies, six of the top 300 U. S. law firms make their global headquarters in the area, while RAND, BNY Mellon, FedEx, Bayer and NIOSH have regional bases that helped Pittsburgh become the sixth-best area for U.
S. job growth. In 2015, Pittsburgh was listed among the "eleven most livable cities in the world"; the region is a hub for Environmental Design and energy extraction. In 2019, Pittsburgh was deemed “Food City of the Year” by the San Francisco-based restaurant and hospitality consulting firm af&co. Many restaurants were mentioned favorable, among them were Superior Motors in Braddock, Driftwood Oven in Lawrenceville, Spork in Bloomfield, Fish nor Fowl in Garfield and Bitter Ends Garden & Luncheonette in Bloomfield. Pittsburgh was named in 1758 by General John Forbes, in honor of British statesman William Pitt, 1st Earl of Chatham; as Forbes was a Scot, he pronounced the name PITS-bər-ə. Pittsburgh was incorporated as a borough on April 22, 1794, with the following Act: "Be it enacted by the Pennsylvania State Senate and Pennsylvania House of Representatives of the Commonwealth of Pennsylvania... by the authority of the same, that the said town of Pittsburgh shall be... erected into a borough, which shall be called the borough of Pittsburgh for ever."
From 1891 to 1911, the city's name was federally recognized as "Pittsburg", though use of the final h was retained during this period by the city government and other local organizations. After a public campaign, the federal decision to drop the h was reversed; the area of the Ohio headwaters was long inhabited by the Shawnee and several other settled groups of Native Americans. The first known European to enter the region was the French explorer/trader Robert de La Salle from Quebec during his 1669 expedition down the Ohio River. European pioneers Dutch, followed in the early 18th century. Michael Bezallion was the first to describe the forks of the Ohio in a 1717 manuscript, that year European fur traders established area posts and settlements. In 1749, French soldiers from Quebec launched an expedition to the forks to unite Canada with French Louisiana via the rivers. During 1753–54, the British hastily built Fort Prince George before a larger French force drove them off; the French built Fort Duquesne based on LaSalle's 1669 claims.
The French and Indian War, the North American front of the Seven Years' War, began with the future Pittsburgh as its center. British General Edward Braddock was dispatched with Major George Washington as his aide to take Fort Duquesne; the British and colonial force were defeated at Braddock's Field. General John Forbes took the forks in 1758. Forbes began construction on Fort Pitt, named after William Pitt the Elder while the settlement was named "Pittsborough". During Pontiac's Rebellion, native tribes conducted a siege of Fort Pitt for two months until Colonel Henry Bouquet relieved it after the Battle of Bushy Run. Fort Pitt is notable as the site of an early use of smallpox for biological warfare. Lord Jeffery Amherst ordered blankets contaminated from smallpox victims to be distributed in 1763 to the tribes surrounding the fort; the disease spread into other areas, infected other tribes, killed hundreds of thousands. During this period, the powerful nations of the Iroquois Confederacy, based in New York, had maintained control of much of the Ohio Valley as hunting grounds by right of conquest after defeating other tribes.
By the terms of the 1768 Treaty of
A davit is any of various crane-like devices used on a ship for supporting and lowering equipment such as boats and anchors. The term sometimes refers to structural arms in other applications where a suspended load is supported in similar fashion to the naval application. Davit systems are most used to lower an emergency lifeboat to the embarkation level to be boarded. Davits can be used as man-overboard safety devices to retrieve personnel from the water; the lifeboat davit has falls that are used to lower the lifeboat into the water. "Davit" can refer to a single mechanical arm with a winch for lowering and raising spare parts onto a vessel and for lowering any other equipment from the deck of a vessel or a pontoon to the water. The maintaining and operation of davits is all under jurisdiction of the International Maritime Organization; the regulations are enforced by the country's own Coast Guard. The development of the davit from its original "goose neck form" to the current devices advanced when A.
P. Schat patented a number of systems in 1926 that allowed the lifeboat to glide over obstructions on a ship's hull, known as the "Schat Skate"; this was followed by a self-braking winch system. The standard became so common that shipyard specifications call for Schat-type davits which are available from various sources. Similar systems developed by Schat companies are used on offshore oil or gas rigs, being placed around the structure. Development of the davit has been in terms of material. Traditionally davits have been made in aluminium or steel but recent advances in composite material have led to the manufacture of davits in carbon fibre which has an excellent power to weight ratio; this means davits can be stowed away when not in use and the same davit used in multiple deck sockets fitted permanently on deck. Davits are designed to fit into deck spaces that the naval architects deemed necessary: Radial — Hand powered davit; this type was used on the lifeboats of the RMS Lusitania. Each arm must be rotated out manually.
Goose-neck shape to the arm, swung out. Mechanical — This type is like the radial davit, but both arms are moved out at the same time using a screw system. An example is the Welin Quadrant davit type used on RMS Titanic. Gravity — There are multiple forms. Roller — Davit slides down a track, bringing the davit to the embarkation deck. Single pivot — One pivot point where the lifeboat is moved over the side of the craft. Multi pivot — Common on promenade decks of cruise ships. Useful where space is limited. Free fall — Lifeboat slides right off vessel. Lifeboat must be an enclosed type. Main type of Davit on merchant ships now; this type does not use. Fixed — Common on oil rigs. Lifeboat is lowered into the water. Liferaft These can be Enclosed enclosed, or open. Frapping Lines These lines are used on all davits except the fixed and freefall davits; the frapping line are used to pull the lifeboat over to the embarkation deck along with the tricing pendent to be loaded. Gripes Ropes used to hold the Lifeboat in the stored position while underway.
Tricing pendants Lines used to pull the lifeboat over to the embarkation deck so that the Frapping lines can be connected. Falls The wires which lift or lower the lifeboat are known. There are 3 basic systems used to release the lifeboat from the davit. On-load: For this style of release mechanism, the lifeboat can be released at any point from the davit; this type of system allows a lifeboat to be released when it is not in the water, whether this is because of the emergency or an accident. Because of this, during an evacuation the release mechanism must be watched to make sure there is not an accidental activation. Offload: This release mechanism requires the weight of the lifeboat to not be on the hook when it is released; this includes the Titanic-era Monomony hook design that requires someone to remove the hook from the lifeboat by hand. But this type includes the hydrostatic system many lifeboats use now. For this, a float is raised up and engages the release once the craft is in the water to the right depth.
Free Fall: This type of release mechanism is basic. The lifeboat slides down and off of the ship when engaged; this is done by pumping a lever, inside the lifeboat by the pilot. If there is not enough hydraulic pressure to release the stop fall, a pump on the inside must be rotated to build up the hydraulic pressure to release the lifeboats stopfall hook. Once the stopfall hook is released the lifeboat will slide into the water; this type of lifeboat is more common due to its quick ease of operation. For all lifeboats using a roller gravity davit and Rottmer releasing gear, this is the procedure: Make sure the Davit tracks are clear of debris Remove the lifeboat cover if applicable Put in the lifeboat plugs At this time the Rottmer releasing gear is checked to be secure. Attach the sea painter to the bow of the ship. Remove the gripes from the lifeboat. Make sure the gripes preventing bar is free from the track. Have the assigned brake man life the braking bar and lower the lifeboat to the embarkation deck.
Now that the Tricing pendants have pulled the lifeboat in close, attach the Frapping lines to the wire falls by passing them to a worker, on the lifeboat. Load t
United States Navy
The United States Navy is the naval warfare service branch of the United States Armed Forces and one of the seven uniformed services of the United States. It is the largest and most capable navy in the world and it has been estimated that in terms of tonnage of its active battle fleet alone, it is larger than the next 13 navies combined, which includes 11 U. S. allies or partner nations. With the highest combined battle fleet tonnage and the world's largest aircraft carrier fleet, with eleven in service, two new carriers under construction. With 319,421 personnel on active duty and 99,616 in the Ready Reserve, the Navy is the third largest of the service branches, it has 282 deployable combat vessels and more than 3,700 operational aircraft as of March 2018, making it the second-largest air force in the world, after the United States Air Force. The U. S. Navy traces its origins to the Continental Navy, established during the American Revolutionary War and was disbanded as a separate entity shortly thereafter.
The U. S. Navy played a major role in the American Civil War by blockading the Confederacy and seizing control of its rivers, it played the central role in the World War II defeat of Imperial Japan. The US Navy emerged from World War II as the most powerful navy in the world; the 21st century U. S. Navy maintains a sizable global presence, deploying in strength in such areas as the Western Pacific, the Mediterranean, the Indian Ocean, it is a blue-water navy with the ability to project force onto the littoral regions of the world, engage in forward deployments during peacetime and respond to regional crises, making it a frequent actor in U. S. foreign and military policy. The Navy is administratively managed by the Department of the Navy, headed by the civilian Secretary of the Navy; the Department of the Navy is itself a division of the Department of Defense, headed by the Secretary of Defense. The Chief of Naval Operations is the most senior naval officer serving in the Department of the Navy.
The mission of the Navy is to maintain and equip combat-ready Naval forces capable of winning wars, deterring aggression and maintaining freedom of the seas. The U. S. Navy is a seaborne branch of the military of the United States; the Navy's three primary areas of responsibility: The preparation of naval forces necessary for the effective prosecution of war. The maintenance of naval aviation, including land-based naval aviation, air transport essential for naval operations, all air weapons and air techniques involved in the operations and activities of the Navy; the development of aircraft, tactics, technique and equipment of naval combat and service elements. U. S. Navy training manuals state that the mission of the U. S. Armed Forces is "to be prepared to conduct prompt and sustained combat operations in support of the national interest." As part of that establishment, the U. S. Navy's functions comprise sea control, power projection and nuclear deterrence, in addition to "sealift" duties, it follows as certain as that night succeeds the day, that without a decisive naval force we can do nothing definitive, with it, everything honorable and glorious.
Naval power... is the natural defense of the United States The Navy was rooted in the colonial seafaring tradition, which produced a large community of sailors and shipbuilders. In the early stages of the American Revolutionary War, Massachusetts had its own Massachusetts Naval Militia; the rationale for establishing a national navy was debated in the Second Continental Congress. Supporters argued that a navy would protect shipping, defend the coast, make it easier to seek out support from foreign countries. Detractors countered that challenging the British Royal Navy the world's preeminent naval power, was a foolish undertaking. Commander in Chief George Washington resolved the debate when he commissioned the ocean-going schooner USS Hannah to interdict British merchant ships and reported the captures to the Congress. On 13 October 1775, the Continental Congress authorized the purchase of two vessels to be armed for a cruise against British merchant ships. S. Navy; the Continental Navy achieved mixed results.
In August 1785, after the Revolutionary War had drawn to a close, Congress had sold Alliance, the last ship remaining in the Continental Navy due to a lack of funds to maintain the ship or support a navy. In 1972, the Chief of Naval Operations, Admiral Elmo Zumwalt, authorized the Navy to celebrate its birthday on 13 October to honor the establishment of the Continental Navy in 1775; the United States was without a navy for nearly a decade, a state of affairs that exposed U. S. maritime merchant ships to a series of attacks by the Barbary pirates. The sole armed maritime presence between 1790 and the launching of the U. S. Navy's first warships in 1797 was the U. S. Revenue-Marine, the primary predecessor of the U. S. Coast Guard. Although the USRCS conducted operations against the pirates, their depredations far outstripped its abilities and Congress passed the Naval Act of 1794 that established a permanent standing navy on 27 March 1794; the Naval Act ordered the construction and manning of six frigates and, by October 1797, the first three were brought into service: USS United States, USS Constellation, USS Constitution.
Due to his strong posture on having a strong standing Navy during this period, John Adams is "often called the father of the American Navy". In 1798–99 the Navy was involved in an undeclared Quasi-War with France. From 18
The metre or meter is the base unit of length in the International System of Units. The SI unit symbol is m; the metre is defined as the length of the path travelled by light in vacuum in 1/299 792 458 of a second. The metre was defined in 1793 as one ten-millionth of the distance from the equator to the North Pole – as a result the Earth's circumference is 40,000 km today. In 1799, it was redefined in terms of a prototype metre bar. In 1960, the metre was redefined in terms of a certain number of wavelengths of a certain emission line of krypton-86. In 1983, the current definition was adopted; the imperial inch is defined as 0.0254 metres. One metre is about 3 3⁄8 inches longer than a yard, i.e. about 39 3⁄8 inches. Metre is the standard spelling of the metric unit for length in nearly all English-speaking nations except the United States and the Philippines, which use meter. Other Germanic languages, such as German and the Scandinavian languages spell the word meter. Measuring devices are spelled "-meter" in all variants of English.
The suffix "-meter" has the same Greek origin as the unit of length. The etymological roots of metre can be traced to the Greek verb μετρέω and noun μέτρον, which were used for physical measurement, for poetic metre and by extension for moderation or avoiding extremism; this range of uses is found in Latin, French and other languages. The motto ΜΕΤΡΩ ΧΡΩ in the seal of the International Bureau of Weights and Measures, a saying of the Greek statesman and philosopher Pittacus of Mytilene and may be translated as "Use measure!", thus calls for both measurement and moderation. In 1668 the English cleric and philosopher John Wilkins proposed in an essay a decimal-based unit of length, the universal measure or standard based on a pendulum with a two-second period; the use of the seconds pendulum to define length had been suggested to the Royal Society in 1660 by Christopher Wren. Christiaan Huygens had observed that length to be 39.26 English inches. No official action was taken regarding these suggestions.
In 1670 Gabriel Mouton, Bishop of Lyon suggested a universal length standard with decimal multiples and divisions, to be based on a one-minute angle of the Earth's meridian arc or on a pendulum with a two-second period. In 1675, the Italian scientist Tito Livio Burattini, in his work Misura Universale, used the phrase metro cattolico, derived from the Greek μέτρον καθολικόν, to denote the standard unit of length derived from a pendulum; as a result of the French Revolution, the French Academy of Sciences charged a commission with determining a single scale for all measures. On 7 October 1790 that commission advised the adoption of a decimal system, on 19 March 1791 advised the adoption of the term mètre, a basic unit of length, which they defined as equal to one ten-millionth of the distance between the North Pole and the Equator. In 1793, the French National Convention adopted the proposal. In 1791, the French Academy of Sciences selected the meridional definition over the pendular definition because the force of gravity varies over the surface of the Earth, which affects the period of a pendulum.
To establish a universally accepted foundation for the definition of the metre, more accurate measurements of this meridian were needed. The French Academy of Sciences commissioned an expedition led by Jean Baptiste Joseph Delambre and Pierre Méchain, lasting from 1792 to 1799, which attempted to measure the distance between a belfry in Dunkerque and Montjuïc castle in Barcelona to estimate the length of the meridian arc through Dunkerque; this portion of the meridian, assumed to be the same length as the Paris meridian, was to serve as the basis for the length of the half meridian connecting the North Pole with the Equator. The problem with this approach is that the exact shape of the Earth is not a simple mathematical shape, such as a sphere or oblate spheroid, at the level of precision required for defining a standard of length; the irregular and particular shape of the Earth smoothed to sea level is represented by a mathematical model called a geoid, which means "Earth-shaped". Despite these issues, in 1793 France adopted this definition of the metre as its official unit of length based on provisional results from this expedition.
However, it was determined that the first prototype metre bar was short by about 200 micrometres because of miscalculation of the flattening of the Earth, making the prototype about 0.02% shorter than the original proposed definition of the metre. Regardless, this length became the French standard and was progressively adopted by other countries in Europe; the expedition was fictionalised in Le mètre du Monde. Ken Alder wrote factually about the expedition in The Measure of All Things: the seven year odyssey and hidden error that transformed the world. In 1867 at the second general conference of the International Association of Geodesy held in Berlin, the question of an international standard unit of length was discussed in order to combine the measurements made in different countries to determine the size and shape of the Earth; the conference recommended the adoption of the metre and the creation of an internatio
The lead ship, name ship, or class leader is the first of a series or class of ships all constructed according to the same general design. The term is applicable to larger civilian craft. Large ships may take as much as five to ten years to construct. Any changes or advances that are available when building a ship are to be included, so it is rare to have two that are identical. Constructing one ship is likely to reveal better ways of doing things and errors; the second and ships are started before the first one is completed and tested. Building copies is still more efficient and cost-effective than building prototypes, the lead ship will be followed by copies with some improvements rather than radically different versions; the improvements will sometimes be retrofitted to the lead ship. The lead ship will be launched and commissioned for shakedown testing before following ships are completed, making the lead ship a combination of template and prototype, rather than expending resources on a prototype that will never see actual use.
Ship classes are named in one of two ways. If a ship class is produced for another fleet, the first active unit will become the lead ship for that fleet. Larger civilian craft, such as Sun Princess, the lead ship of the Sun-class cruise ships, sometimes follow this convention as well. Example of a lead ship announcement from US Navy USS Pennsylvania BB-38