Mk47

Deployed on the Polaris A1(UGM-27A) & A2(UGM-27B) Submarine-Launched Ballistic Missile (SLBM)._{1.1, 13.1}

Proposed as the “light” warhead for application with the Skybolt (GAM-87) missile_10.1

In service from April 1960_19.1 to 1974 with 1,360 weapons produced._14.1

In January 1960, the delivery date for early production Mk47s was delayed by the Navy until June. The first of an emergency-capability version of the warhead, the EC-47 were assembled and stored by Sandia on April 30, 1960. In June, the EC-47s were replaced in storage by production-model Mk47s. The first 16 Mk47 Mod 0 warheads were delivered to the Navy in July 1960 and on November 15, 1960, the USS George Washington with 16 armed Polaris (UGM-27A) missiles sailed from Charleston, South Carolina, on its first operational patrol._19.3 Approximately 300 EC-47 warheads were produced between April and June 1960 with all being retired in June._19.4

Approximately 1,060 warheads were produced between June 1960 and July 1964 with all being retired by November 1974._19.4

Used a mechanical safing device that withdrew a cadmium/boron neutron absorbing wire from the interior of the Robin primary. This safing device was in response to the failed one-point safety test in during Operation Hardtack II, shot Neptune, with this modification designating the warhead Mk47Y1. This system ended up proving unreliable and it was not until after the Atomic Energy Commission (AEC) resumed full-scale testing in 1960 that the safety problem was resolved._14.2

As a result of a test conducted on a deliberately corroded Robin primary, it was found that despite heavy corrosion the primary could still produce a yield within an acceptable range to trigger the supplementary stage. This finding prompted the replacement of around 20% of deployed Mk47 primaries. A design change in the Robin primary prevented future corrosion, and was incorporated into the Mk47Y2 Mod 2 warhead._19.3

In December 1961, the Mk47 Mod 1 was design released for production, while during that same month while undergoing routine stockpile surveillance, significant corrosion of the fissile materials in the primary of several weapons was found indicating that, if detonated, the weapons would not achieve a full yield._19.3

In November 1962, the Mk47Y2 Mod 2 was released for production, with early production beginning at the end of February 1963._19.3

During stockpile surveillance inspections of Mk47s in 1963, it was discovered that the mechanical arming systems of the Mk47Y1 and Mk47Y2 did not always function properly and complete the firing circuit, resulting in a dud weapon. The failure of the arming mechanism was traced to an underpowered motor, friction caused by material build-up from chemical reactions on the surfaces of some components, and to inadvertent crimping of some other components during production. The stockpile of Mk47s were radiographed for evidence of these problems, in addition, a more powerful arming motor was installed. At the time of this problem, three-quarters of the stockpiled Mk47s were the Y2 Mod 2 version. Livermore estimated that 75% of these warheads would fail, reducing the total Mk47 stockpile by 50%. Overcoming this engineering problem proved difficult, there was no lubricant that could be used without risking future damage to other warhead components. The Mk47Y2 was tested in a full-scale underground test without the mechanical safing system to determine inherent one-point safety. A yield of 100 tons, similar to that from the Hardtack II, shot Neptune of October 1958, showed that the Mk47 was still not one-point safe. _19.4

Mk47 warhead production was completed in July 1964.

During the first stockpile surveillance inspection of the Y2 Mod 2 warheads in August 1965, it was found that the mechanical safing system in a number of Y2 Mod 2 primaries operated only halfway, which would have resulted in a dud weapon. At first, this appeared to be an isolated problem, however it was discovered again in late 1966. Friction appeared to increase in the arming system as it aged, more rapidly in Y2 Mod 2 warheads but with evidence that the mechanical arming system in the Y1 would also eventually fail._19.4

In an attempting to solve this engineering problem, features of another inherently one-point safe Livermore-designed warhead were proposed for addition to the Mk47. These changes entailed removing the mechanical safing system, reducing the amount of high explosives, and adding more plutonium to make up for the resulting loss in compression. Further small-scale underground nuclear tests showed the new configuration to both be one-point safe and capable of full-yield detonation. Starting in March 1965, the Atomic Energy Commission (AEC) proceeded to rebuild the entire Mk47 stockpile, incorporating these tested addition into what would become the Y2 Mod 3 configuration. This conversion was completed by late 1967._19.4

In 1962_20.1 It was found that, during a test, the material in the Mk47 primary was vulnerable to effects encountered in a potential antiballistic missile environment._2.3

Jointly designed by Dr. Edward Teller, Foster, Brown, and Jack Rosengren._10.2

Both the Los Alamos Scientific Laboratory (LASL) and the University of California Radiation Laboratory (UCRL) were requested to participate in the study, but the major effort was provided by the Radiation Laboratory._11.1 The Mk47 was 46.6″ long, 18″ in diameter, with the Y1 configuration weighing 717-720lbs and Y2 733lbs._9.19 Mk47Y1 has a yield of 600Kt_9.16 and Mk47Y2 a yield of 1.2Mt_{6.1, 9.18}

The Mk47Y1 used the Robin primary and the Piccolo supplementary stage_18.1, entering Phase 6 Quantity Production in June 1960._17.1

The Mk47Y2 used the Robin primary_4.1 and Fife supplementary stage._9.2

The Mk47Y2 Mod 3 used the Kinglet primary._18.2

Later modification utilized a spherical supplementary stage._15.1

The first weapon to utilize highly-enriched uranium (HEU) within its secondary stage, instead of natural or depleted uranium._3.1

The Mk47 was the first thermonuclear weapon to use enriched uranium-235 as the tamper surrounding the secondary in-place of depleted or natural uranium._8.1

The firing set would contain an environmental safety switch, neutron generators, X-unit, chopper-converters and firing circuits, and would be sealed as an entity at assembly. The firing set would then be mated to the warhead and subsequently require only continuity and humidity testing._11.3

Was the first weapon to utilize Sandia’s Livermore environmental testing complex, operated by the Environmental Test Division 8283, composed of the Environmental Test Facility (Bldg. 955) and the Dynamic Test Facility (Bldg. 956)_12.1

During testing, it was found that there were problems with the fissile material corroding, that it was vulnerable when placed into a simulated Anti-Ballistic Missile (ABM) environment and that it had issues with its one-point safety design._2.1 With the one-point safety issue being an inherent problem with the original primary, a new primary was selected and subsequently the Mk47 needed to undergo a nuclear test to ensure this new design was satisfactory to the services requirements._2.2

Used the H694 Warhead Hand Truck_16.1