W47

W47. The W47 was an American thermonuclear warhead developed for the Polaris submarine-launched ballistic missile, a cornerstone of the United States Navy's strategic deterrent during the Cold War. It was the first such warhead to be both lightweight and compact enough for deployment on a submarine-based missile, representing a significant technological achievement by Lawrence Livermore National Laboratory under the direction of physicist Edward Teller. The warhead entered service in 1960 but was plagued by serious reliability issues with its Argonne National Laboratory-designed firing set, leading to a major retrofit program.

Design and development

The development of the W47 was driven by the urgent need for a warhead compatible with the small size and weight constraints of the UGM-27 Polaris missile, a key component of the Nuclear triad. The design team at Lawrence Livermore National Laboratory, competing against Los Alamos National Laboratory, pioneered a two-stage thermonuclear design utilizing concepts like Radiation implosion and a fission-fusion process. A critical and ultimately problematic component was the MC2892 arming and fuzing system, which included a novel Betatron-inspired firing set designed to generate a high-voltage pulse for the warhead's primary stage. The warhead's development was part of a broader acceleration of American nuclear weapons programs following the launch of Sputnik 1 and during the tenure of Secretary of Defense Robert McNamara.

Specifications

The W47 had a published yield of 600 kilotons in its initial Y1 model, though some sources suggest a yield of 800 kt for the later Y2 variant. It weighed approximately 720 pounds (330 kg), a critical parameter for the Polaris A-1 and Polaris A-2 missiles. The physical specifications were dictated by the missile's Re-entry vehicle geometry, known as the Mark 1 re-entry vehicle. The warhead's internal components included a Plutonium-based Primary stage and a Lithium deuteride Secondary stage, with the entire system engineered for extreme ruggedness to withstand the forces of submarine launch and Atmospheric reentry.

Operational history

The W47 entered service with the United States Navy in 1960 aboard the USS George Washington (SSBN-598), the first American Ballistic missile submarine. Its deployment marked a transformative shift in Nuclear strategy, providing an invulnerable second-strike capability. However, operational reliability was severely compromised by failures in the MC2892 firing set; estimates suggested a high probability of failure if launched. This crisis led to the W47Y2 modification program, overseen by Sandia National Laboratories, which replaced the faulty components. Despite these fixes, concerns persisted, contributing to the warhead's retirement in the mid-1970s as the Polaris system was succeeded by the Poseidon missile armed with the W68 warhead.

Variants

Two main production variants of the warhead were manufactured. The original W47Y1 was the model deployed from 1960, containing the flawed Argonne National Laboratory firing set. The extensively modified W47Y2 variant was the product of the reliability retrofit program, incorporating a new, more conventional firing set developed by Sandia National Laboratories. Some sources also reference a W47Y0 prototype model used in early flight tests. The Y2 modification was so extensive it was essentially a new warhead, with all deployed Y1 units eventually being converted to the Y2 standard to maintain the credibility of the Fleet Ballistic Missile force.

Survivors

As a retired nuclear weapon component, no complete W47 warheads are on public display. The high-explosive pits and other inert components are likely stored in secure facilities managed by the Department of Energy or the Department of Defense. Examples of the Polaris missile and its Mark 1 re-entry vehicle, which contained the W47, can be seen at several museums, including the National Museum of the United States Navy in Washington, D.C. and the Steven F. Udvar-Hazy Center in Chantilly, Virginia. The warhead's design legacy influenced subsequent compact warheads like the W58 and the W68. Category:American nuclear warheads Category:Cold War nuclear weapons of the United States Category:Lawrence Livermore National Laboratory