The W56 (originally called the Mark 56 ) was an American thermonuclear warhead produced starting in 1963 which saw service until 1993, on the Minuteman I and II ICBMs .
68-468: The warhead had a yield of 1.2 megatonnes of TNT (5.0 PJ) and a demonstrated yield-to-weight ratio of 4.96 kilotonnes of TNT per kilogram (20.8 petajoules per tonne ), very close to the predicted 5.1 kilotonne of TNT/kg (21 PJ/t) achievable in the highest yield to weight weapon ever built, the 25 megatonnes of TNT (100 PJ) B41 . However unlike the B41, which was never tested at full yield,
136-448: A Department of Energy investigation into the laboratory. The investigation found that the "missing plutonium" was a result of miscalculation by LANL's statisticians and did not actually exist; but the investigation did lead to heavy criticism of the laboratory by the DOE for security flaws and weaknesses that the DOE claimed to have found. LANL is northern New Mexico's largest institution and
204-422: A nuclear weapon . The TNT equivalent appears in various nuclear weapon control treaties , and has been used to characterize the energy released in asteroid impacts . Alternative values for TNT equivalency can be calculated according to which property is being compared and when in the two detonation processes the values are measured. Where for example the comparison is by energy yield, an explosive's energy
272-542: A drum containing nuclear waste was ruptured due to a ' deflagration ' according to an inspector general report of the Dept. of Energy, which due to lab mistakes, also occurred in 2014 at the Carlsbad plant with significant disruptions and costs across the industry. In 2009, 69 computers which did not contain classified information were lost. The same year also saw a scare in which 1 kg (2.2 lb) of missing plutonium prompted
340-409: A file server, a batch server, a printer and graphics output server and numerous other general purpose and specialized systems. IBM Roadrunner , which was part of this network, was the first supercomputer to hit petaflop speeds. Until 1999, The Los Alamos National Laboratory hosted the arXiv e-print archive. The arXiv is currently operated and funded by Cornell University . The coreboot project
408-408: A gram of TNT upon explosion. Thus one can state that a nuclear bomb has a yield of 15 kt ( 6.3 × 10 J ), but the explosion of an actual 15,000 ton pile of TNT may yield (for example) 8 × 10 J due to additional carbon/hydrocarbon oxidation not present with small open-air charges. These complications have been sidestepped by convention. The energy released by one gram of TNT
476-844: A new requirement for the use of external initiation and a chopper-converter firing set was added. This produced the XW-56-X2 warhead. It was decided that the XW-56-X1 would no longer be designated the Mark 56 Mod 1, but that the XW-56-X2 would instead take the Mod 1 nomenclature. The warhead was design released in May 1962 and production began in March 1963. The warhead was 17.4 inches (440 mm) in diameter, 47.3 inches (1,200 mm) long and weighed 600 pounds (270 kg), and fitted to
544-453: A photo nearly led to a criticality incident. The photo shoot, which was directed by the laboratory's management, was one of several factors relating to unsafe management practices that led to the departure of 12 of the lab's 14 safety staff. The criticality incident was one of several that led the Department of Energy to seek alternative bids to manage the laboratory after the 2018 expiration of
612-521: A precise source of data. Los Alamos National Laboratory Los Alamos National Laboratory (often shortened as Los Alamos and LANL ) is one of the sixteen research and development laboratories of the United States Department of Energy (DOE), located a short distance northwest of Santa Fe, New Mexico , in the American southwest . Best known for its central role in helping develop
680-444: A secure area within the laboratory, but were later found behind a photocopier. Los Alamos National Laboratory's mission is to "solve national security challenges through simultaneous excellence". The laboratory's strategic plan reflects U.S. priorities spanning nuclear security, intelligence, defense, emergency response, nonproliferation, counterterrorism, energy security , emerging threats, and environmental management. This strategy
748-637: A third accident occurred during an annual physical inventory in December 1958. Several buildings associated with the Manhattan Project at Los Alamos were declared a National Historic Landmark in 1965. At the end of the Cold War , both labs went through a process of intense scientific diversification in their research programs to adapt to the changing political conditions that no longer required as much research towards developing new nuclear weapons and has led
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#1732851478528816-411: Is a unit of energy equal to 4.184 terajoules ( 4.184 × 10 J ). A kiloton of TNT can be visualized as a cube of TNT 8.46 metres (27.8 ft) on a side. The " megaton (of TNT equivalent)" is a unit of energy equal to 4.184 petajoules ( 4.184 × 10 J ). The kiloton and megaton of TNT equivalent have traditionally been used to describe the energy output, and hence the destructive power, of
884-860: Is aligned with priorities set by the Department of Energy (DOE), the National Nuclear Security Administration (NNSA), and national strategy guidance documents, such as the Nuclear Posture Review , the National Security Strategy , and the Blueprint for a Secure Energy Future. Los Alamos is the senior laboratory in the DOE system , and executes work in all areas of the DOE mission: national security, science, energy, and environmental management. The laboratory also performs work for
952-436: Is normally expressed for chemical purposes as the thermodynamic work produced by its detonation. For TNT this has been accurately measured as 4,686 J/g from a large sample of air blast experiments, and theoretically calculated to be 4,853 J/g. However even on this basis, comparing the actual energy yields of a large nuclear device and an explosion of TNT can be slightly inaccurate. Small TNT explosions, especially in
1020-442: Is reported to have nearly detonated in 2005 when an unsafe amount of pressure was applied to the explosive while it was being disassembled. The W56 program began with the need for two new warheads to arm Weapons System WS-133A , later known as Minuteman. The study, released in March 1958, suggested that two warhead designs be produced; a 330-pound (150 kg) warhead and a 550-pound (250 kg) warhead. These warheads were to have
1088-484: Is the approximate energy released in the detonation of a metric ton (1,000 kilograms) of TNT . In other words, for each gram of TNT exploded, 4.184 kilojoules (or 4184 joules ) of energy are released. This convention intends to compare the destructiveness of an event with that of conventional explosive materials , of which TNT is a typical example, although other conventional explosives such as dynamite contain more energy. The " kiloton (of TNT equivalent)"
1156-461: The Army-Navy "E" Award for Excellence in production on October 16, 1945. After the war, Oppenheimer retired from the directorship, and it was taken over by Norris Bradbury , whose initial mission was to make the previously hand-assembled atomic bombs "G.I. proof" so that they could be mass-produced and used without the assistance of highly trained scientists. Other founding members of Los Alamos left
1224-491: The Department of Defense (DoD), Intelligence Community (IC), and Department of Homeland Security (DHS), among others. The laboratory's multidisciplinary scientific capabilities and activities are organized into six Capability Pillars: Los Alamos operates three main user facilities: As of 2017, the Los Alamos National Laboratory is using data and algorithms to possibly protect public health by tracking
1292-737: The Human Immunodeficiency Virus were being tested by lab scientist Bette Korber and her team. "These vaccines might finally deal a lethal blow to the AIDS virus ", says Chang-Shung Tung, leader of the Lab's Theoretical Biology and Biophysics group. The laboratory has attracted negative publicity from a number of events. In 1999, Los Alamos scientist Wen Ho Lee was accused of 59 counts of mishandling classified information by downloading nuclear secrets—"weapons codes" used for computer simulations of nuclear weapons tests—to data tapes and removing them from
1360-496: The Lawrence Livermore National Laboratory (LLNL). The two labs competed on a wide variety of bomb designs, but with the end of the Cold War , have focused increasingly on civilian missions. Today, Los Alamos conducts multidisciplinary research in fields such as national security , space exploration , nuclear fusion , renewable energy , medicine , nanotechnology , and supercomputing . While owned by
1428-478: The Mark 11 reentry vehicle. In December 1962, it was noted that efforts were being made to harden the warhead against blast effects such as those from anti-ballistic missile systems. The decision was made to change the way the warhead was mounted to the reentry vehicle. Instead of a single flange, a honeycomb sleeve would be placed between the warhead and reentry vehicle, and would provide area loading. This interim design,
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#17328514785281496-455: The Mark 56 Mod 1 had a planned availability date of April 1963. A series of flight tests of the warhead were conducted from July 1962 and the planned production date was May 1963. In June 1961 a new production date of February 1963 was requested alongside increased early production rates, but after discussing the difficulties in meeting this goal, the request was dropped. However, in January 1962,
1564-718: The National Science Foundation , LANL operates one of the three National High Magnetic Field Laboratories in conjunction with and located at two other sites Florida State University in Tallahassee, Florida , and University of Florida in Gainesville, Florida . Los Alamos National Laboratory is a partner in the Joint Genome Institute (JGI) located in Walnut Creek, California . JGI was founded in 1997 to unite
1632-592: The University of Texas System partnered with Lockheed-Martin . In December 2005, the Department of Energy announced that LANS had won the next seven-year contract to manage and operate the laboratory. On June 1, 2006, the University of California ended its sixty years of direct involvement in operating Los Alamos National Laboratory, and management control of the laboratory was taken over by Los Alamos National Security, LLC with effect October 1, 2007. Approximately 95% of
1700-467: The XW-56-X3 was given the production nomenclature Mark 56 Mod 2 . The design was not interchangeable with the Mod 1 warhead and production was planned for April 1964. The Mod 2 design was, with minor exceptions, identical to the Mod 1 design. Changes included new inertial switches as the originals could not survive the shocks involved, and a new neutron generator redesigned to improve the mounting system for
1768-497: The first atomic bomb , LANL is one of the world's largest and most advanced scientific institutions. Los Alamos was established in 1943 as Project Y , a top-secret site for designing nuclear weapons under the Manhattan Project during World War II . Chosen for its remote yet relatively accessible location, it served as the main hub for conducting and coordinating nuclear research, bringing together scientists from around
1836-509: The flow cytometry technology. In the 1950s, researcher Mack Fulwyler developed a technique for sorting erythrocytes that combined the Coulter Principle of Coulter counter technologies, which measures the presence of cells and their size, with ink jet technology, which produces a laminar flow of liquid that breaks up into separate, fine drops. In 1969, Los Alamos reported the first fluorescence detector apparatus, which accurately measured
1904-613: The LANL director no longer reports to the UC Regents or UC Office of the President. On June 8, 2018, the NNSA announced that Triad National Security, LLC, a joint venture between Battelle Memorial Institute , the University of California, and Texas A&M University, would assume operation and management of LANL beginning November 1, 2018. In August 2011, the close placement of eight plutonium rods for
1972-579: The LANS contract. The lab was penalized with a $ 57 million reduction in its 2014 budget over the February 14, 2014, accident at the Waste Isolation Pilot Plant for which it was partly responsible. In August 2017, the improper storage of plutonium metal could have triggered a criticality accident , and subsequently staff failed to declare the failure as required by procedure. With support of
2040-514: The Manhattan Project, Los Alamos hosted thousands of employees, including many Nobel Prize -winning scientists. The location was a total secret. Its only mailing address was a post office box, number 1663, in Santa Fe , New Mexico. Eventually two other post office boxes were used, 180 and 1539, also in Santa Fe. Though its contract with the University of California was initially intended to be temporary,
2108-574: The Minuteman program and requested a new availability date from Sandia who replied that the main restraint on availability was the need for six warhead flight tests approximately one year before production could begin. If the W47 was used without change, the tests could be completed by December 1959 but if the warhead was modified tests could extend by as much as a year. In August the Joint Chiefs of Staff assigned
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2176-459: The Mod 4 warhead have been declassified other than that it may have weighed 680 pounds (310 kg). The weapon had separate engineering and production (mod numbered) names. TNT equivalent TNT equivalent is a convention for expressing energy , typically used to describe the energy released in an explosion. The ton of TNT is a unit of energy defined by convention to be 4.184 gigajoules ( 1 gigacalorie ), which
2244-604: The Navy's W47 warhead for Polaris A-1 . Little action was taken on these findings during 1958 however, due to a lack of Minuteman funding. A second feasibility study was published in March 1959 which reported that the weight of the W47 could be reduced and that as the US had suspended nuclear testing , focus on a design that did not require testing was required. Later that month, the Air Force Special Weapons Center accelerated
2312-508: The Secretary-Treasurer Robert Underhill, who was in charge of wartime contracts and liabilities. The work of the laboratory culminated in several atomic devices, one of which was used in the first nuclear test near Alamogordo, New Mexico , codenamed " Trinity ", on July 16, 1945. The other two were weapons, " Little Boy " and " Fat Man ", which were used in the attacks on Hiroshima and Nagasaki. The Laboratory received
2380-682: The W56 demonstrated its efficiency in the XW-56-X2 Bluestone shot of Operation Dominic in 1962. Production of the Mod 1 warhead began in March 1963. The Mod 4 warhead began production in May 1967 and finished production in May 1969. 1,000 total were produced, of which 455 were Mod 4 warheads. The warheads were retired between 1991 and 1993, and the last W56 warhead was dismantled in June 2006. During dismantlement, one warhead which had high-performance but sensitive polymer-bonded explosive in its explosive lenses
2448-459: The XW-56 would be used instead. By August 1960 however, it became clear that Minuteman's production scheduled has slipped, and that producing the XW-56 as an interim warhead was less necessary, leading to questions as to if development of both weapons slowed the development of the XW-56-X1. The Radiation Laboratory believed that there was some benefit to having the less advanced but tested XW-56 alongside
2516-484: The country indicated the need for a laboratory dedicated solely to that purpose. General Leslie Groves wanted a central laboratory at an isolated location for safety, and to keep the scientists away from the populace. It should be at least 200 miles from international boundaries and west of the Mississippi. Major John Dudley suggested Oak City, Utah , or Jemez Springs, New Mexico , but both were rejected. Jemez Springs
2584-782: The country's nuclear arsenal. Additional work included basic scientific research, particle accelerator development, health physics, and fusion power research as part of Project Sherwood . Many nuclear tests were undertaken in the Marshall Islands and at the Nevada Test Site . During the late-1950s, a number of scientists including Dr. J. Robert "Bob" Beyster left Los Alamos to work for General Atomics (GA) in San Diego . Three major nuclear-related accidents have occurred at LANL. Criticality accidents occurred in August 1945 and May 1946, and
2652-403: The development names XW-56 and XW-56-X1 were assigned to the program. Though derived from the W47, Sandia believed that as the non-nuclear components of the weapon would be lighter than those in the W47, with the gross warhead weight of the XW-56 being about 670 pounds (300 kg). As no new materials were required by the program and all components were used in other projects, early production
2720-747: The effectiveness of the United States' vaccine distribution infrastructure. Additional advancements include the ASPECT airplane that can detect bio threats from the sky. In 2008, development for a safer, more comfortable and accurate test for breast cancer was ongoing by scientists Lianjie Huang and Kenneth M. Hanson and collaborators. The new technique, called ultrasound-computed tomography (ultrasound CT), uses sound waves to accurately detect small tumors that traditional mammography cannot. The lab has made intense efforts for humanitarian causes through its scientific research in medicine. In 2010, three vaccines for
2788-402: The environment. It also contributed to thousands of dumpsites at 108 locations in 29 US states. Continuing efforts to make the laboratory more efficient led the Department of Energy to open its contract with the University of California to bids from other vendors in 2003. Though the university and the laboratory had difficult relations many times since their first World War II contract, this was
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2856-420: The expertise and resources in genome mapping , DNA sequencing , technology development, and information sciences pioneered at the three genome centers at University of California's Lawrence Berkeley National Laboratory (LBNL), Lawrence Livermore National Laboratory (LLNL), and LANL. The Integrated Computing Network (ICN) is a multi-security level network at the LANL integrating large host supercomputers,
2924-426: The explosive. This enables engineers to determine the proper masses of different explosives when applying blasting formulas developed specifically for TNT. For example, if a timber-cutting formula calls for a charge of 1 kg of TNT, then based on octanitrocubane 's RE factor of 2.38, it would take only 1.0/2.38 (or 0.42) kg of it to do the same job. Using PETN , engineers would need 1.0/1.66 (or 0.60) kg to obtain
2992-496: The federal government, LANL is privately managed and operated by Triad National Security, LLC . The laboratory was founded during World War II as a secret, centralized facility to coordinate the scientific research of the Manhattan Project , the Allied project to develop the first nuclear weapons . In September 1942, the difficulties encountered in conducting preliminary studies on nuclear weapons at universities scattered across
3060-525: The first time that the university ever had to compete for management of the laboratory. The University of California decided to create a private company with the Bechtel Corporation, Washington Group International , and the BWX Technologies to bid on the contract to operate the laboratory. The UC/Bechtel led corporation— Los Alamos National Security, LLC (LANS)—was pitted against a team formed by
3128-493: The former 10,000 plus UC employees at LANL were rehired by LANS to continue working at LANL. Other than UC appointing three members to the eleven member board of directors that oversees LANS, UC now has virtually no responsibility or direct involvement in LANL. UC policies and regulations that apply to UC campuses and its two national laboratories in California ( Lawrence Berkeley and Lawrence Livermore ) no longer apply to LANL, and
3196-467: The generator. The new reentry vehicle was called the Mark 11A . With the warhead in its reentry vehicle the total system was 32 inches (810 mm) in diameter, 80.5 inches (2,040 mm) long and weighed 831 pounds (377 kg). Production was achieved in August 1964. In May 1966, Sandia National Laboratories and Livermore began work on a hard (high energy) x-ray hardening program for the W56. The exact changes made are still classified, but one portion
3264-625: The growth of infectious diseases . Digital epidemiologists at the lab's Information Systems and Modeling group are using clinical surveillance data, Google search queries, census data, Misplaced Pages , and even tweets to create a system that could predict epidemics. The team is using data from Brazil as its model; Brazil was notably threatened by the Zika virus as it prepared to host the Summer Olympics in 2016 . Within LANL's 43-square-mile property are approximately 2,000 dumpsites which have contaminated
3332-502: The lab to increase research for "non-war" science and technology. Los Alamos' nuclear work is currently thought to relate primarily to computer simulations and stockpile stewardship . The development of the Dual-Axis Radiographic Hydrodynamic Test Facility will allow complex simulations of nuclear tests to take place without full explosive yields. The laboratory contributed to the early development of
3400-448: The lab. After ten months in jail, Lee pleaded guilty to a single count and the other 58 were dismissed with an apology from U.S. District Judge James Parker for his incarceration. Lee had been suspected for having shared U.S. nuclear secrets with China , but investigators were never able to establish what Lee did with the downloaded data. In 2000, two computer hard drives containing classified data were announced to have gone missing from
3468-477: The laboratory and became outspoken opponents to the further development of nuclear weapons. The name officially changed to the Los Alamos Scientific Laboratory ( LASL ) on January 1, 1947. By this time, Argonne had already been made the first National Laboratory the previous year. Los Alamos would not become a National Laboratory in name until 1981. In the years since the 1940s, Los Alamos
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#17328514785283536-490: The largest employer with approximately 8,762 direct employees, 277 guard force, 505 contractors, 1,613 students, 1,143 unionized craft workers, and 452 post-doctoral researchers. Additionally, there are roughly 120 DOE employees stationed at the laboratory to provide federal oversight of LANL's work and operations. Approximately one-third of the laboratory's technical staff members are physicists , one-quarter are engineers , one-sixth are chemists and materials scientists , and
3604-510: The maximum achievable yield within the specified weight and have an operational deployment date of mid-1962. A feasibility study group met 5 May 1958 and having been asked to complete the study quickly, concluded after one day that the lightweight warhead requirement could be met through a modification of the W50 used in MGM-31 Pershing while the heavy warhead could be developed through a rework of
3672-498: The more advanced but untested XW-56-X1, but field command believed there was no advantage to a mixture of tested and untested warheads, and instead requested that only the XW-56-X1 be produced. In December the Division of Military Applications cancelled the XW-56 warhead program. In September 1960, XW-56-X1 apparently received a new primary stage design, developed by Los Alamos National Laboratory . The proposed ordnance characteristics of
3740-406: The number and size of ovarian cells and blood cells. As of 2017, other research performed at the lab included developing cheaper, cleaner biofuels and advancing scientific understanding around renewable energy. Non-nuclear national security and defense development is also a priority at the lab. This includes preventing outbreaks of deadly diseases by improving detection tools and the monitoring
3808-433: The open, don't tend to burn the carbon-particle and hydrocarbon products of the explosion. Gas-expansion and pressure-change effects tend to "freeze" the burn rapidly. A large open explosion of TNT may maintain fireball temperatures high enough so that some of those products do burn up with atmospheric oxygen. Such differences can be substantial. For safety purposes a range as wide as 2,673–6,702 J has been stated for
3876-444: The relationship was maintained long after the war. Until the atomic bombings of Hiroshima and Nagasaki , Japan , University of California president Robert Sproul did not know what the purpose of the laboratory was and thought it might be producing a " death ray ". The only member of the UC administration who knew its true purpose—indeed, the only one who knew its exact physical location—was
3944-437: The requirements for the warhead. They established a maximum warhead diameter of 20 inches (510 mm), a length of 60 inches (1,500 mm) and a weight of 600 pounds (270 kg), with the highest possible yield obtainable in this weight and package size. AVCO Manufacturing were assigned development of the reentry vehicle. In September, the military characteristics were specified and required ground and air burst fuzing, that
4012-671: The same effects as 1 kg of TNT. With ANFO or ammonium nitrate , they would require 1.0/0.74 (or 1.35) kg or 1.0/0.32 (or 3.125) kg, respectively. Calculating a single RE factor for an explosive is, however, impossible. It depends on the specific case or use. Given a pair of explosives, one can produce 2× the shockwave output (this depends on the distance of measuring instruments) but the difference in direct metal cutting ability may be 4× higher for one type of metal and 7× higher for another type of metal. The relative differences between two explosives with shaped charges will be even greater. The table below should be taken as an example and not as
4080-525: The warhead require minimal servicing and that it be able to be left unattended for up to 3 years at a time. The warhead was to contain no primary power source unless the use of a ferromagnetic X-unit was required, and it would contain an environmental safing device located in the warhead in a manner as to minimize the possibility of a sabotage nuclear detonation. Development of the warhead was initially assigned to Lawrence Radiation Laboratory and in November 1959
4148-454: The weapon states that the warhead would be connected to the reentry vehicle though a single flange that provided cantilevered support of the warhead. This helped relieve thermal expansion issues between the warhead and reentry vehicle. The warhead also included a system to prevent transfer of boosting gas to the pit in the event of a fire. The warhead received approval as the Minuteman warhead on 13 October 1960. The XW-56-X1 warhead, now called
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#17328514785284216-473: The world, among them numerous Nobel Prize winners. The town of Los Alamos , directly north of the lab, grew extensively through this period. After the war ended in 1945, Project Y's existence was made public, and it became known universally as Los Alamos. In 1952, the Atomic Energy Commission formed a second design lab under the direction of the University of California, Berkeley , which became
4284-507: Was arbitrarily defined as a matter of convention to be 4,184 J, which is exactly one kilocalorie . 1 ton of TNT equivalent is approximately: The relative effectiveness factor (RE factor) relates an explosive's demolition power to that of TNT, in units of the TNT equivalent/kg (TNTe/kg). The RE factor is the relative mass of TNT to which an explosive is equivalent: The greater the RE, the more powerful
4352-764: Was initially developed at LANL. In the recent years, the Laboratory has developed a major research program in systems biology modeling , known at LANL under the name q-bio. Several serials are published by LANL: LANL also published Los Alamos Science from 1980 to 2005, as well as the Nuclear Weapons Journal , which was replaced by National Security Science after two issues in 2009. In 2005, Congress held new hearings on lingering security issues at Los Alamos National Weapons Laboratory in New Mexico; documented problems continued to be ignored. In November 2008,
4420-487: Was only a short distance from the current site. Project Y director J. Robert Oppenheimer had spent much time in his youth in the New Mexico area and suggested the Los Alamos Ranch School on the mesa . Dudley had rejected the school as not meeting Groves' criteria, but as soon as Groves saw it he said in effect "This is the place". Oppenheimer became the laboratory's first director; from 19 October 1942. During
4488-419: Was responsible for the development of the hydrogen bomb , and many other variants of nuclear weapons. In 1952, Lawrence Livermore National Laboratory was founded to act as Los Alamos' "competitor", with the hope that two laboratories for the design of nuclear weapons would spur innovation. Los Alamos and Livermore served as the primary classified laboratories in the U.S. national laboratory system, designing all
4556-500: Was scheduled from mid-1962. Concurrently, the XW-56-X1 was developed. The warhead was to be an improved XW-56, but by August 1960, the Radiation Laboratory believed in treating the XW-56-X1 as an entirely new weapon, taking advantage of all possible design improvements. The intention at this point was for the XW-56-X1 to arm Minuteman, but if missiles were to become operational before the planned stockpile entry date of July 1963,
4624-506: Was the inclusion of a forward shield. The modified warhead was designated the XW-56-X4 and given the production nomenclature of Mark 56 Mod 3 . Existing Mod 2 warheads were retrofitted to the Mod 3 design. Early production was achieved in February 1967. A final weapon, the Mark 56 Mod 4 began development in March 1967. The program was to further harden the weapon against the effects of x-rays. Production began in May 1967. No further details of
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