The US Nuclear Arsenal: Minuteman, the W47, and the MIRV Failure
W59 - High-power ammunition
W59 - thermonuclear nuclear warhead (nuclear charge device, physical package) with an estimated energy release of 800 kt (3,2 PJ). From 1962 to 1969, this charge was equipped with a limited number of missiles - three squadrons, about 150 units, which determined the circulation of charges. We are talking about the first modification of the Minuteman ICBM, the LGM-30A (Minuteman IA). This same charge was planned to be the main warhead of the GAM-87 Skybolt air-to-ground ballistic missile (carried by a B-52), but the project was cancelled. Based on the American design, the WE.177 charge was developed in the UK, according to several sources, and it was used as a free-fall bomb by the Royal Air Force and the Navy. aviation countries until the mid-1990s.
Development of the world's first solid-fuel, compact (launch weight 29 tons) intercontinental ballistic missile Minuteman 1 The program was authorized in February 1958. By March, research on a possible warhead for the new missile had been completed, and in April, the Lawrence Livermore National Laboratory (LLNL) warhead concept, the future XW-56 (the designation itself would be assigned later, in November 1959), was approved for further development. The program required significant effort and was plagued by funding problems.
The project's interim details and timelines remain classified. It is only known that in December 1960, or even earlier, the Air Force decided to play it safe: it approved a second program, a high-yield warhead (over 1 megaton) for the Minuteman. Production was scheduled to begin in July 1962, with full-scale production scheduled for December 1962. The work was assigned to LLNL's more experienced competitor, LANL. In March 1961, this warhead was designated XW-59.
In January 1961, the joint working group on Mark 5 warheads, already busy mating the XW-56 nuclear payload to this warhead, was tasked with doing the same with the XW-59 warhead. By early 1961, the military had not yet decided on a warhead for the Minuteman missile, their top priority. In May 1961, a second, separate group was formed to work on the new Mark 11 warhead type. The Mark 11 warheads were planned to be operational in January 1963, and then replace all Mark 5 warheads on the missiles.
In May 1961, Avco and Sandia National Laboratory joined forces to adapt the charge to the new warhead. The warhead was to be compatible with the Skybolt ASBM system, and all electrical components, except for external initiators, were already in mass production. Safety was ensured by three solutions: the warhead lacked its own power source, used electrostatic dischargers, and detonation required two trigger signals in the correct order.
Flight tests of the warheads were conducted in late 1961, and the Mark 59 Mod 0 warhead design was presented in December 1961. The Minuteman's operational entry into service was delayed due to a series of accidents: all 10 initial launches (July–September 1962) were unsuccessful. Nevertheless, the warhead production schedule remained on track, and the first warhead was delivered as planned in June 1962. The final report on the Mark 59 Mod 0 noted that the warhead met all design requirements, with the exception of several classified items. A total of 150 W59 warheads were fired from June 1962 to July 1963. By June 1969, all of them were retired from service.
W56 is a three-stage device
W56 (originally designated Mark 56) is a three-stage thermonuclear device produced from 1963 and deployed on the Minuteman IB and Minuteman II intercontinental ballistic missiles until 1993. It had an estimated yield of 1,2 megatons of TNT (5,0 petajoules), and demonstrated a yield-to-weight ratio of 4,96 kilotons per kilogram of nuclear payload (20,8 petajoules/ton). This is very close to the estimated specific yield of 5,1 kilotons/kg (21 petajoules/ton).
The B41 bomb had the highest specific energy release among three-stage warheads (the first stage being fission with fusion illumination, the second stage being fusion with fission of the uranium shell, and the third stage being fission of the shell by fast neutrons) used by the US military, producing 25 megatons of TNT equivalent (100 petajoules). However, the B41 was never tested at full yield. The W56, on the other hand, confirmed its calculated characteristics with a full-scale detonation during a test. Bluestone.
Production of the first model W56 (Mod 1) began in March 1963. The next and final modification, Mod 4, was produced from May 1967 to May 1969. A total of approximately 1000 warheads of all modifications (Mods 1–4) were manufactured; the final Mod 4 accounted for 455 units. They were withdrawn from service between 1991 and 1993, and the last W56/Mk11 block was dismantled in June 2006. It was reported that during dismantling in 2005, one of the warheads nearly detonated: its explosive lenses contained a highly effective but sensitive polymer-bonded explosive, and it was subjected to unsafe shock pressure during disassembly.
The W56 program began with a US Department of Defense technical specification (TTS) for the development of two new warheads for the WS-133A weapon system. American media at the time reported that the Air Force was exploring new solid-fuel, small-size ICBM designs for the WS-133A: Murok, Midgetman (this name would be given to another ICBM project a quarter of a century later) and Mightyman. It is known about the Muroc, for example, that it was supposed to have a 24% lighter takeoff weight and 37% shorter length than the Minuteman. The company's Minuteman won the competition. Boeing.
A study published in March 1958 initially proposed two types of nuclear warheads for the Minuteman: a 330-pound (150 kg) and a 550-pound (250 kg) version. These were to have the highest possible yield for a given weight and be fielded in mid-1962. The feasibility study group met on May 5, 1958. Tasked with completing the work as quickly as possible, the following day it concluded that the requirement for a lightweight warhead could be met by modifying the W50 nuclear warhead from the MGM-31A ballistic missile. Pershing, and the heavy warhead should be developed on the basis of the W47 from the SLBM Polaris A-1However, in 1958, these findings remained without consequences due to a lack of funding for the program.
In March 1959, a second feasibility study was released. It stated that the W47 warhead's weight could be further reduced, although it was already at the limit of what was possible for its yield class. Since the US had suspended nuclear testing, it was necessary to focus on a design that did not require detonation testing, i.e., one based on an already proven design. Later that month, the Air Force Special Warfare Center accelerated the Minuteman program and requested a new warhead entry date from Sandia. Sandia responded that the main obstacle was the need to conduct six flight tests of the warheads approximately a year before production began. If the W47 had been used unchanged, testing would have been completed by December 1959, but with extensive modifications, it would have been delayed for at least a year.
In August 1960, the Joint Chiefs of Staff approved the warhead requirements: a maximum diameter of 20 inches (510 mm), a length of 60 inches (1500 mm), and a weight of 600 pounds (270 kg), with the maximum yield possible within these dimensions. Development of the warhead and automatic control unit was assigned to Avco Manufacturing.
The American two-stage solid-fuel ballistic missile UGM-27 Polaris A-1
The W47 is a masterpiece let down by its execution.
The W47 deserves special mention. This masterpiece of scientific, technical, and engineering thought from the late 1950s remains an unrivaled design, but only in theory, as its technical execution let it down.
In the fall of 1956, at a Department of Defense meeting attended by all the design engineers, Frank E. Boswell, head of the Naval Ordnance Test Station, raised the issue of solid-fuel submarine-launched ballistic missiles: a launch weight of no more than 30,000 pounds, a range of 1000 to 1500 miles. He then addressed the nuclear weapons developers:
“Can you build a compact 1000-pound, 1-megaton device in five years?”
Los Alamos representatives immediately refused. Edward Teller in his memoirs (Memoirs, 2001) writes:
"I stood up and said, 'We at Livermore can build it in five years, and it will yield one megaton.' When I returned to Livermore and told my guys about the work ahead, their hair stood on end. They replied, 'What have you done? We can't build such a device in such a short time.'"
Companies took on the rocket Lockheed (now Lockheed Martin) and AerojetThe program was named Polaris, and already on September 24, 1958, the first (emergency) launch of the rocket took place Polaris A-1X from a ground-based launcher. The next four also failed, and only on April 20, 1959, the next launch was successful. At this time fleet redesigned one of his projects, a multi-purpose nuclear submarine (MPNS) "Scorpio" (SSN-589), the world's first nuclear-powered ballistic missile submarine "George Washington" (SSBN-598). Its surface displacement was 6019 tons, and its submerged displacement was 6880 tons. To achieve this, a 40-meter section with 16 vertical launch tubes was built into the submarine's central section, behind the retractable launcher enclosure (conning tower). The missile's circular error probable (CEP) at its maximum range of 2200 kilometers was 1800 meters. The missile was equipped with a Mk-1 single-warhead separating in flight with a W47 thermonuclear warhead.
Ultimately, Teller and his team succeeded in creating the W47 nuclear warhead, which was revolutionary for its time. It was very compact (460 mm in diameter and 1200 mm in length) and weighed 330 kg (in the Mk-1/Y1 warhead casing) or 332 kg (Mk-1/Y2). The Y1 modification formally had a yield of 600 kt (2,5 PJ), and “formally” because during tests, as will be shown below, the charge did not reach the calculation; the Y2 was theoretically twice as powerful - 1,2 Mt (5,0 PJ). The W47/Mk-1 warhead block weighed 1000 pounds (454 kg) when loaded. These very high figures, even by modern standards, were achieved by a three-stage design. According to recently declassified British documents, the W47 contained:
- 2,5 kg (5,5 lb) plutonium core, 95% Pu-239 (SCUA 5/5 primary module);
- 60 kg (130 lb) third stage uranium sleeve, U-238;
- 36 kg (79 lb) lithium deuteride in the secondary module;
- 4 grams (0,14 oz) tritium - neutron generator.
It's completely unclear why it was necessary to launch two new and rather expensive programs, the W59/Mk5 and W56/Mk5, for the Minuteman when a decent warhead of the same high yield (1,2 megatons) and comparable warhead weight (up to 1000 pounds, approximately 450 kg) was already available. At first glance, it simply needed some polishing, and that alone would have been cheaper than two new, massively expensive programs on the same topic. Adapting the W47 to Minuteman warheads, both the Mk5 and the later Mk11, is precisely the job for Sandia, and a mere pittance at that. That's exactly what the USSR did: universalization is the law of a planned economyApparently, Americans are unaware of the Russian proverb, "The best is the enemy of the good," or another one, "Don't look for good from good." True, as further developments will show story, the scale of the W47's defects was not yet clear at that time, and "finishing it" turned out to be a far from trivial task.
The fact is that the W47 had serious reliability issues. In 1966, 75% of the 300 units of the most powerful Y2 modification were considered faulty and could not be used. It is interesting to look at the test history of the XW47 device: it contains more objective and accurate information about the actual yield of this nuclear device than any reference book on the Polaris SLBM. Of the six explosions in 1958, the first four were tests of the primary modules (plutonium fuses); all of them produced a yield close to the calculated one, from 0,3 kt (unboosted) to 20 kt. The last two tests of the nuclear device were conducted at full power: the first, Aspen (June 14, 1958), yielded 319 kt, and the second, Redwood (June 27, 1958), 412 kt. As a result of all this fuss with a revolutionary and innovative charge, Edward Teller did not fulfill his promise of reliability: as operation showed, the device turned out to be unreliable and significantly underpowered.
Return to the W56: From XW-56 to Mod 4
In September 1960, the requirements for the Minuteman nuclear warhead were clarified. It was to have a fuse for ground and air detonation, require minimal maintenance, and last up to three years without maintenance. Furthermore, the warhead was to be stripped of its primary neutron source (generator) and equipped with an environmental sensing device (ESD) that would only allow arming under normal conditions; it was to be positioned internally to minimize the likelihood of an unauthorized (sabotaged) nuclear detonation. Development was initially assigned to LLNL, and in November 1959, the program was designated XW-56 and XW-56-X1.
The XW-56 nuclear warhead was based on the W47, but Sandia believed that the non-nuclear components would be lighter, bringing the total weight of the device to approximately 670 pounds (300 kg). Since no new materials were required and all components were used in other projects, production was planned to begin as early as mid-1962. In parallel, the XW-56-X1/Mk5A warhead, an improved version of the XW-56/Mk5, was being developed. However, by August 1960, LLNL decided to consider the XW-56-X1/Mk5A as an entirely new design. weapon, which takes into account all possible improvements. It was originally planned to be installed on the Minuteman, but if the missiles had been operational before the scheduled July 1963 replenishment, the XW-56 would have been used instead.
By August 1960, it had become clear that the Minuteman's production schedule was slipping and the XW-56/Mk5 interim warhead was no longer necessary. The question arose: would the simultaneous development of two types slow down the development of the XW-56-X1/Mk5A and compromise it? LLNL believed it would be beneficial to have the less advanced but proven XW-56/Mk5 alongside the more advanced, but incompletely tested XW-56-X1/Mk5A. Air Force command, on the other hand, saw no advantage in combining proven and untested warheads and demanded that only the XW-56-X1/Mk5A be produced. In December, the Office of War Applications canceled the XW-56 program. In September 1960, the XW-56-X1 nuclear warhead apparently received a new design from Los Alamos National Laboratory, and on October 13, 1960, the warhead was approved for the Minuteman.
The XW-56-X1 nuclear warhead, now designated the Mark 56 Mod 1, was scheduled for delivery in April 1963. A series of flight tests of the Mark 11 warhead had been underway since July 1962, with production planned for May 1963. In June 1961, a new date of February 1963 was requested, along with an acceleration of early production, but after discussing the difficulties, the request was rejected. In January 1962, a new requirement was added: an external initiator and a fully digital automation unit. This gave birth to the XW-56-X2 warhead. It was decided that the previous XW-56-X1 would lose the Mark 56 Mod 1 designation; the Mod 1 serial designation would now be assigned to the new version, the XW-56-X2. R&D on this nuclear missile was completed by May 1962, and production began in March 1963.
The assembled nuclear warhead had a diameter of 17,4 inches (440 mm), a length of 47,3 inches (1200 mm), and weighed 600 pounds (270 kg). The loader and automation unit were installed in the Mark 11 warhead casing. In December 1962, it was noted that efforts were being made to protect the warhead from shock waves, such as those caused by the detonation of nuclear warheads in anti-ballistic missiles. A decision was made to change the method of attaching the payload to the platform: instead of a single flat steel flange between the warhead and the platform cell, a duralumin honeycomb adapter panel was installed, which uniformly absorbed the shock load. This interim design, the XW-56-X3/Mk5A, received the serial designation W56 Mod 2/Mk11. It was not interchangeable with the W56 Mod 1/Mk5 warhead, and its production was planned to begin in April 1964.
The W56 Mod 2/Mk11 design, with a few exceptions, was identical to the W56 Mod 1/Mk11. Changes included the inertial accelerometers, which had failed under shock loads (they were replaced with new ones), and an improved neutron generator. As a result of such lengthy and meticulous refinement, the new warhead was designated the Mark 11A. The total weight of the warhead, including the casing and automation unit (excluding the KSP PRO—the missile defense penetration system) was 831 pounds (377 kg). The warhead had a cone base diameter of 32 inches (810 mm) and a length (cone height) of 80,5 inches (2040 mm). However, the overall throw-weight of the W56/Mk11, compared to the older W56/Mark 5 (the early design variant discussed above), still increased significantly, from 370 to 590 kg, due to the inclusion of ten Tracor Mk11 decoys in the warhead, which simulated the radar cross-section, infrared signature, and velocity of the actual warhead. Production of the W56/Mk11 began in August 1964.
In May 1966, Sandia and LLNL began a program to improve the W56/Mk11's hardness against high-energy X-rays. The exact list of modifications remains classified, but one of them was the addition of a forward (nose) shield. The modified nuclear warhead was designated XW-56-X4 and the serial number W56 Mod 3. Existing Mod 2 warheads were upgraded to the Mod 3 standard, with the first deliveries occurring in February 1967.
Development of the final model, the W56 Mod 4, began in March 1967 and pursued the same goal—further protection against X-rays. Production began in May 1967. Further details about the Mod 4 have not been disclosed; only information has leaked to the press about the increase in yield for this particular modification to 2 megatons (while earlier modifications, on which the calculations above are based, yielded 1,2 megatons), and about the fact that the nuclear loader itself became slightly heavier, to 680 pounds (310 kg).
To be continued
Information