The Department of Energy is readying the Nevada Test Site for a large-scale, open-air, high explosive detonation on a tunnel complex. The Defense Threat Reduction Agency (DTRA), the DOE customer which is conducting the test, is stressing that the test is not a nuclear blast and the Russian government reportedly has been notified to avoid misunderstanding about the event. "The test is aimed at determining how well a massive conventional bomb would perform against fortified underground targets," the Washington Post reported on March 31st.

No one - with the notable exception of Andrew Lichterman and John Fleck who first reported on this - seems to have tried to dig deeper than the press release from DTRA. I too have monitored the preparations for Divine Strake; It is much more than was reported (for media reports about Divine Strake after publication of this Nuclear Brief, click here).

Divine Strake is neither a bomb nor conventional. Instead, the test is a detonation of a pile of chemical explosives to simulate a "low-yield nuclear weapon ground shock" effect to "improve the warfighter’s confidence in selecting the smallest proper nuclear yield necessary to destroy underground facilities while minimizing collateral damage."

Divine Strake, moreover, is an integral part of STRATCOM's new Global Strike mission, which is otherwise said to provide mainly non-nuclear means of defeating time-critical targets. Divine Strake is the first nuclear effects simulation of this kind against underground targets since President George W. Bush in Summer 2004 directed STRATCOM to "extend Global Strike to counter all HDBTs [Hard and Deeply Buried Targets] to include both tactical and strategic adversarial targets." (see guidance overview here)

The Divine Strake Event

Divine Strake was approved in 2002 as part of the congressionally authorized DOD FY2002 Tunnel Target Defeat Advanced Concept and Technology Demonstration (ACTD). Since then, DTRA has prepared for the event under its Counterforce program. DTRA confirmed today that Divine Strake is the event described in the budget documents. The DTRA counterforce RDT&E (Research, Development, Testing and Engineering) budget for FY2006 described the experiment this way:

"Conduct the Tunnel Target Defeat Advanced Concept and Technology Demonstration(s) (ACTD) Full-Scale tunnel defeat demonstration using high explosives to simulate a low yield nuclear weapon ground shock environment at Department of Energy's Nevada Test Site."

The reference to low-yield nuclear weapons was omitted from the section in the FY2007 budget request, which instead describes the event like this: "Conduct the Tunnel Target Defeat ACTD large-scale tunnel defeat demonstration using high explosives to produce the desired ground shock environment at the Department of Energy's Nevada Test Site." Yet the nuclear reference is used elsewhere in the FY2007 budget:

Divine Strake reflects a concern in the Pentagon over what is said to be an increasing number of a underground facilities in potentially hostile countries. The 2001 Nuclear Posture Review warned that the existing B61-11 nuclear earth-penetrator does not have sufficient capability against certain deeply buried targets. The Robust Nuclear Earth Penetrator was supposed to provide additional capability, but Congress has refused to fund the weapon due to concern that it could lower the nuclear threshold.

Divine Stake is not an RNEP-type experiment because it simulates the use of a very low-yield nuclear weapon against an relatively shallow underground target. Divine Strake follows a previous 3D computer simulation conducted by scientists at Los Alamos National Laboratory in 2004, which examined the use of a 10 kt nuclear detonation inside the U16B tunnel as an agent defeat weapon. The experiment concluded that the relatively large yield was necessary for radiation to penetrate through the entire length of the tunnel "indicating that such yields might be necessary to guarantee agent destruction stored inside large tunnel complexes."

Divine Strake, in contrast, does not simulate agent defeat destruction but simply envisions using the explosive yield of a small nuclear weapon to destroy or severely damage and underground structure. Also important is that the simulation is not directed against the tunnel entrances, but involves detonating the explosives on top of the surface above the tunnel.

The contract for collecting the seismo-acoustic data from Divine Strake was awarded to Southern Methodist University on March 16, 2006.

The "Weapon"

Contrary to most of the media reports, Divine Strake is not testing a conventional bomb but simply detonates a huge pile (700 tons) of Ammonium Nitrate and Fuel Oil (ANFO). For comparison, the largest conventional weapon in the U.S. inventory is the MOAB (Massive Ordnance Air Blast) bomb, which contains nearly nine tons of explosives with a yield of approximately 0.012 kt TNT.

The explosive power of Divine Strake will be approximately 593 tons of TNT equivalent, or roughly 0.6 kt. This is about double the lowest yield option on the non-strategic B61 nuclear gravity bomb, and suggests that Divine Strake may be intended to fine-tune use of the B61 bomb. There are three modifications of the non-strategic B61 bomb in the U.S. stockpile with yields ranging from 0.3 kt to 170 kt.

The B61 also exists in a strategic version (B61-7) with four yields up to 350 kt, but given the strategic mission of this weapon the lowest yield option may be higher than the non-strategic version. Finally, the B61-11 has a single yield of 400 kt.

Divine Strake is not the first large-scale, open-air, high explosive detonation conducted by DTRA. Such events apparently play an important role in fine-tuning the plans for using nuclear weapons against underground and surface targets. Since 1977, at least 10 similar events have been carried out at the White Sands Missile Range in New Mexico. The events have involved from 24 tons to as much as 4,744 tons of high explosives.

Other detonations have included an underground detonation of 1,410 tons in the U12n tunnel at NTS in 1993. In addition, Seven 120-ton detonations were carried out at Misers Bluff at Planet Ranch in Arizona in 1978. Finally, in 2002, an 18 tons explosion was set off at the Nevada Test Site.

Experience obtained from these detonations were used to develop the plans for Divine Strake scheduled for June 2, 2006, at the U16B tunnel complex at the Nevada Test Site.

The U16B Tunnel Complex

Divine Strake will be conducted at the U16B complex on the Nevada Test Site. U16B consists of a hook-shaped tunnel drilled through a limestone formation and connected to three portals and a vent hole. Each of the tunnel entrances are sealed by large steel doors 14x13 feet and 1.5 foot thick.

The target

The U16B target was "carefully chosen" for Divine Strake so that it "simulates the characteristics of important potential, global adversaries," according to the DOE. The detonation will be conducted in a limestone bed with specific geological properties, according to the DOE's draft environmental assessment for Divine Strake: "As a number of potential adversarial military targets are based in similar limestones, [Divine Strake] needed to be sited in a similar geological setting to actual military targets."

According to the DOE, such HDBTs are used by adversaries for command and control, storage of munitions (including weapons of mass destruction, and long-range missiles), modern air defenses, a variety of tactical weapons, wartime refuge for national leaders, and a multitude of other offensive and defensive military uses.

An example of such a target may be the Chinese airbase at Feidong, which includes what appears to be a large underground facility for hiding aircraft and potentially also other of the capabilities mentioned by DOE.