In the Summer of 1991, a team of Los Alamos nuclear weapons scientists delivered a briefing to the Defense Science Board, provocatively titled "Potential Uses for Low-Yield Nuclear Weapons in the New World Order."
Shortly after Bill Clinton entered the White House, Representatives John Spratt (D-S.C.) and Elizabeth Furse (D-Ore.) introduced an attachment to the FY 1994 defense authorization bill, prohibiting U.S. weapons labs from conducting any research and development on low-yield nuclear weapons. The measure, which was passed and signed into law by President Clinton, defined low-yield nukes as having a yield of five kilotons or less.
Destroying a target buried 1,000 feet into rock would require a nuclear weapon with the yield of 100 kilotons. That is 10 times the size of the bomb dropped on Hiroshima. Even the effects of a small bomb would be dramatic. A 1-kiloton nuclear weapon detonated 20 to 50 feet underground would dig a crater the size of Ground Zero in New York and eject 1 million cubic feet of radioactive debris into the air. Detonating a similar weapon on the surface of a city would kill a quarter of a million people and injure hundreds of thousands more.
Nuclear weapons cannot be engineered to penetrate deeply enough to prevent fallout. Based on technical analysis at the Nevada Test Site, a weapon with a 10-kiloton yield must be buried deeper than 850 feet to prevent spewing of radioactive debris. Yet a weapon dropped from a plane at 40,000 feet will penetrate less than 100 feet of loose dirt and less than 30 feet of rock. Ultimately, the depth of penetration is limited by the strength of the missile casing. The deepest current earth penetrators, the B61 Mod 11, can burrow is 20 feet of dry earth. Casing made of even the strongest material cannot withstand the physical forces of burrowing through 100 feet of granite, much less 850 feet.
The Nuclear Posture Review (NPR) states that the number, composition, and character of the nation's nuclear forces ought to reflect the reality that the Cold War is over and that required capabilities may now need to be different. For example, current weapons in the stockpile cannot hold at risk a growing category of potential targets deeply buried in tunnel facilities, possibly containing chemical, biological, nuclear, or command and control facilities. As a result the NPR endorsed NNSA's Advanced Concepts Initiative that could provide options that could be considered for future production and deployment against Hard and Deeply Buried Targets [HDBT]. Also, as required by the NPR, it would provide an opportunity for NNSA and its contractors to exercise critical skills necessary for the long-term sustainment of the nation's defense.
The Bush administration envisioned Robust Nuclear Earth Penetrator (RNEP) as a weapon to destroy deep underground targets, while others believe the B-61 Mod 11, a weapon already in the arsenal, accomplishes that goal. The study of a Robust Nuclear Earth Penetrator evaluated modifications to existing nuclear weapons that do not require nuclear testing. The outcome of an RNEP study would be a recommendation to proceed with selective modifications to existing weapons that would ultimately strengthen deterrence by improving the credibility of strategic forces against hard and deeply buried facilities.
In the 2001 Defense Authorization Bill, the Congress directed NNSA to study whether it could take an existing nuclear weapon and encase it in such a way so that it will penetrate the earth before it explodes. The intent is to hold at risk hard and deeply buried targets.
One effort to improve the US capability against HBDTs is a joint DoD/DOE phase 6.2/6.2A Study started in April 2002. This effort will identify whether an existing warhead in a 5,000 pound class penetrator would provide significantly enhanced earth penetration capabilities compared to the B61 Mod 11. Livermore is working on modifying the existing B-83 gravity bomb, while Los Alamos is studying modifications to the B-61 bomb.
By direction of the Nuclear Weapons Council, and in response to an Air Force requirement, the initial focus of the Advanced Concepts Program was the Robust Nuclear Earth Penetrator, for which $15.5 million was requested in FY 2003 as part of the Directed Stockpile Research and Development activity. The three-year RNEP Feasibility Study was to assess the feasibility of modifying one of two candidate nuclear weapons currently in the stockpile to provide enhanced penetration capability into hard rock geologies and develop out-year costs for the subsequent production phases, if a decision is made by the Nuclear Weapons Council to proceed. This work complies with existing legislation, including section 3136 of the FY 1994 National Defense Authorization Act. The FY 2003 budget contains no other funds for Phase 6.X advanced concept study activities. The Congress authorized the budget request of $15 million for the Robust Nuclear Earth Penetrator, but prohibited expenditure of these funds until the Secretary of Defense submits a report setting forth: 1) the military requirements for the RNEP; 2) the nuclear weapons employment policy for the RNEP; 3) the detailed categories or types of targets that the RNEP is designed to hold at risk; and 4) an assessment of the ability of conventional weapons to address the same types of categories of targets that the RNEP is designed to hold at risk.
The FY2004 budget request for the Advanced Concepts program ($21m) included $15 million allocated to the Robust Nuclear Earth Penetrator. This program will examine whether or not two existing warheads in the stockpile -- the B61 and the B83 -- can be sufficiently hardened through case modifications and other work to allow the weapons to survive penetration into various geologies, with high reliability, before detonating. The remaining funds will be divided between the weapons laboratories for studies of other advanced concepts work. Feasibility and Cost Studies were to include the NWC-approved Robust Nuclear Earth Penetrator (RNEP) study (subject to Secretary of Defense Report required by Section 3146 of P.L.107-314, Bob Stump National Defense Authorization Act for FY 2003).
On 16 September 2003, the Senate considered two amendments to the Energy and Water Development Appropriations Act for FY 2004 that would prohibit the use of Department of Energy funds for nuclear weapons development. An amendment authored by Senator Dianne Feinstein (D-CA) that would have eliminated the $6 million in the bill for the Advanced Concepts Initiative. That amendment, which was defeated by a vote of 53-41, also would have reduced funding for the Robust Nuclear Earth Penetrator (RNEP). Senator Feinstein's amendment would have specifically prohibited the use of funds for Department of Energy activities relating to the Robust Nuclear Earth Penetrator, Advanced Weapons Concepts, modification of the readiness posture of the Nevada Test Site, and the Modern Pit Facility. Senator Reed's amendment, which prohibited the use of funds for certain activities relating to advanced nuclear weapons concepts, including the robust nuclear earth penetrator, later passed the Senate in a voice vote.
The Stockpile Services Robust Nuclear Earth Penetrator line item received $14,577,000 in FY2003 and $7,435,000 in FY2004. The Stockpile Services Robust Nuclear Earth Penetrator (RNEP) category includes funding for the completion of the Phase 6.2/2A Air Force-led study. Activities include participating in integrated NNSA-DoD project teams for development of operational requirements; systems design and integration; development of data downselect packages; planning and cost analysis; phenomenology studies; and the executive joint study group. It also includes managing multi-laboratory independent review team activities, and preparing and conducting hardware demonstration tests for candidate designs. In FY 2005 the request for $27,577,000 was intended to cover subsystem tests and a full system test of the proposed design will be completed. All NNSA headquarters and laboratory activities for the RNEP study are coordinated with complementary activities by the Air Force's Air Combat Command and Air Armament Center in conjunction with the responsible directorate of the Air Staff (AF/XON).
On October 25, 2005 US Senator Pete Domenici indicated that negotiators working toward an agreement on funding for the Department of Energy for FY2006 had agreed to drop funding for continued research on the Robust Nuclear Earth Penetrator (RNEP) project at the request of the National Nuclear Security Administration. Domenici is chairman of the Senate Energy and Water Development Appropriations Subcommittee and was leading the Senate contingent working with the House to reconcile differences in the FY2006 Energy and Water Appropriations Bill-among them funding for RNEP. Domenici indicated that at the request of the NNSA, the Senate has agreed to drop the $4.0 million it provided in its bill for the DOE national laboratories, including Sandia National Laboratories, to continue RNEP research. The House bill had no funding for RNEP. "The focus will now be with the Defense Department and its research to earth penetrating technology using conventional weaponry. The NNSA indicated that this research should evolve around more conventional weapons rather than tactical nuclear devices. With this department change in policy, we have agreed not to provide DOE with funding for RNEP," Domenici said.