B61-11 Earth-Penetrating Weapon
The W-61 EPW (earth penetrating warhead) project began in 1989. The EPW was a derivative of the B61-7, packaged in a high-strength steel case, and had gotten as far as production engineering in 1991.
The B61-11 is a new Mod of the B61 being converted from existing B61 Mod 7s. The basic differences in the two Mods are in the nose and tail configurations, and the elimination of the B61-7 parachute and gas generator. The similarities are that all B61-11 internal case hardware and components, including the IHE physics package and warhead electrical system, are from the B61-7. Some sources suggest that the B61-11 has a "dial-a-yield" feature, allowing its yield to range from less than a kiloton to several hundred kilotons. When configured to have a 10-kiloton yield and detonated 4 feet underground, the B61-11 can produce a shock wave sufficient to crush a bunker buried beneath 100 meters of layered rock. However, the December 2001 Nuclear Posture Review noted that "This single-yield, non-precision weapon cannot survive penetration into many types of terrain in which hardened underground facilities are located."
Stockpiled since 1968, the veteran B61 has been modified many times over the years to update its performance. Its latest modification is the B61 Mod 11 "earth-penetrater." The United States deployed the B61-11 bomb in the mid-1990s for an earth penetrating mission. The B61-11 is a new Mod of the B61 being converted from existing B61 Mod 7s. The basic differences in the two Mods are in the nose and tail configurations, and the elimination of the B61-7 parachute and gas generator. The similarities are that all B61-11 internal case hardware and components, including the IHE physics package and warhead electrical system, are from the B61-7.
Designed to replace the aging B53 "laydown" weapon, the much smaller and less powerful B61 can produce the same destructive ground shock as the massive B53, but without the collateral damage associated with a surface blast. The B61-11 was designed not to penetrate rock but to attack only certain targets in hard or frozen soil in Russia.
The B61-11 can penetrate and detonate below the earth's surface, creating a massive shock wave capable of destroying underground targets. In tests the bomb penetrates only 20 feet into dry earth, even when dropped from altitudes above 40,000 feet. But even this shallow penetration before detonation allows a much higher proportion of the explosion to transferred into ground shock relative to a surface burst. It is not able to counter targets deeply buried under granite rock. Moreover, it has a high yield, in the hundreds of kilotons. If used in North Korea, the radioactive fallout could drift over nearby countries such as Japan.
The B61-11 earth-penetrating weapon replaced the huge B53 weapon that had been in the stockpile for years. In October 1993, Harold Smith, Assistant to the Secretary of Defense for Atomic Energy, sought approval to develop an alternative to the B53 high-yield nuclear bomb, which was the principal "bunker buster" weapon in the U.S. arsenal. The B53 was also the heaviest payload nuke in use, weighing 8,900 pounds, and only deployable from the B-52 bombers. Under the guise of "weapons modernization," Smith was pushing the development of the B61-Mod 11.
By November 1993 the Nuclear Weapons Command Standing Safety Committee had approved the B61-11 proposal. On Feb. 6, 1995, Deputy Secretary of Defense John Deutch, a veteran of the Reed Panel advisory board, signed off on the plan. The project was placed on a fast track: On April 18, 1995, the Department of Energy made a classified request to six Congressmen to get funding for the B61-11. The money was flowing by July 1995. On Nov. 15, 1995 Smith pressed for the weapons labs to accelerate the R&D timetable, so the first B61-11 could be delivered to the military before the end of 1996.
The B61-11 was developed and put into the stockpile without full-scale nuclear tests. Some critics have maintained that the B61-11 is a new nuclear weapon, but the US has said all along that the B61-11 is not new, but a modification of older B61s to give the weapon an earth-penetrating capability to destroy buried targets. The new modification and proposed design of the B61 nose assembly incorporates new radar hardware and sophisticated structured elements to withstand the high-shock environments. Sandia's work involved repackaging the B61-7 nuclear and electrical systems into an earth penetrator case. The aft portion of the bomb was outfitted with ballast and a drag flare.
The B61-11 entered the stockpile as a field retrofit. The retrofit, performed by a DOE/DoD team, consisted of repackaging the B61-7 nuclear and electrical systems into an earth penetrator case. The aft portion of the bomb was outfitted with ballast and a drag flare. Production and qualification activities within the nuclear weapon complex was on an accelerated basis. Flight testing was done at the Tonopah Test Range and was supported by a variety of aircraft including the B-2A, B-52, F-15E, and F-16.
Starting in 1995 Sandia Lab's Center 9800 provided USSTRATCOM with operational analysis and planning tools for the B61-11 earth penetrating weapon. This support included evaluating fratricide concerns, optimizing delivery with the B-2, and working to maximize both aircraft survivability and weapon effectiveness. In 1999 Center 9800 led an interagency group to understand more fully the weapon's penetration capabilities.
Sandia has supported retrofits and improvements of the enduring stockpile systems to extend the life of the W87 warhead on the Peacekeeper; an improved radar for the B83 bomb; safety and use control upgrades for the B61 tactical bombs; and a strengthened center case for the B61 earth penetrator.
During 1999 B61-11 alteration (ALT) 349 units were produced and delivered to the Air Force. Alt 349 is a structural modification to the B61-11 to improve performance under certain impact conditions. Qualification activities have included three cable pull-down tests, two B-2A airdrops and a horizontal actuator shock test series. Cable pull-down testing consists of suspending units 300 ft in the air from a cable above a concrete target and pulling the unit down with rockets. In addition to testing, extensive finite element modeling has confirmed test results and contributed significantly to the overall design effort.
In the spring of 2000, Livermore's Hardened Engineering Test Facility shock tested part of the B61 bomb. This version of the B61 bomb must penetrate the earth before it detonates, so it encounters severe shock. The lab's 4-meter-high drop test machine can simulate that tremendous shock. For this kind of test, mock high explosive is wrapped around a plutonium pit inside an aluminum case. The case has flanges that simulate the mounting to a warhead case. It is mounted to the test fixture, which in turn is mounted to the drop machine's carriage. When the test unit is dropped, the speed of its fall usually depends just on gravity. (Although in the testing of Los Alamos's B61, carefully arranged bungee cords pull the test fixture downward to create acceleration and velocities greater than those that could be achieved by gravity.) The unit comes down onto a chunk of steel that is suspended on hydraulic cylinders -- to isolate the rest of the machine from the shock pulse. The steel is layered with felt to calibrate the shock pulse to known shock data for the test unit. The test is performed just once with plutonium in the mock warhead, but practice runs assure that velocities, shock pulse, and other parameters are properly calibrated. Before the shock test, the plutonium pit is radiographed. Afterward, the whole test assembly is radiographed to ensure there are no broken pieces. Then it is disassembled, and the pit is radiographed alone to see what changes, if any, occurred during the test. In the case of the B61, no change or damage resulted from the test.
In 2001 Sandia completed work to qualify the B61-11 earth-penetrating bomb as meeting all requirements, resulting in its acceptance as a standard stockpile item. We made alterations to enhance the safety and security of all B61 bombs at field locations. In recognizing the efforts of the B61-11 certification team, the Commander-in-Chief of Strategic Command cited the weapon's many advantages over the retired B53-1 bomb.
DOD synthetic environments are virtual representations of the physical and behavioral phenomena of complex military systems achieved through mathematical modeling, simulation, and simulators. This is the environment within which DOD's goal of "virtual prototyping" and "exploration of future warfighting concepts" will be accomplished. More importantly, this environment will be used in analysis and decision support for combat development, material acquisition, test and evaluation, and training processes. For the past several years, LANL has contributed MSA efforts to help develop DOD synthetic environments. USSTRATCOM has requested that LANL develop and provide them with a B61-11 engagement planning tool for use in end-to-end weapon/target engagement analysis.