Seymour Hersh is at it again.
Suggest the US will nuke Iran:
One of the military’s initial option plans, as presented to the White House by the Pentagon this winter, calls for the use of a bunker-buster tactical nuclear weapon, such as the B61-11, against underground nuclear sites. One target is Iran’s main centrifuge plant, at Natanz, nearly two hundred miles south of Tehran. Natanz, which is no longer under I.A.E.A. safeguards, reportedly has underground floor space to hold fifty thousand centrifuges, and laboratories and workspaces buried approximately seventy-five feet beneath the surface. … The elimination of Natanz would be a major setback for Iran’s nuclear ambitions, but the conventional weapons in the American arsenal could not insure the destruction of facilities under seventy-five feet of earth and rock, especially if they are reinforced with concrete.
Let’s leave aside the fact that Natanz is still under IAEA safeguards and that UK Foreign Secretary called the idea of a nuclear strike against Natanz “completely nuts.”
Is Natanz so deep that a nuclear weapon is necessary?
Iranian officials claim Natanz is more than 18 meters underground. Hersh suggests 23 meters. Anyway, you get the picture—Natanz is about 20 meters undeground. (Dissidents NCRI claim the facility is only 8 meters underground. I wonder if Iranian officials were counting from the ceiling or the floor.)
Depth, though, is less important than the “thickness” or “concrete overburden equivalent” of a Hard and Deeply Buried Target (HDBT). Natanz was constructed using the “cut and cover” method—first, dig a hole, thenbuild a reinforced concrete roof, cover with rock and soil, and repeat. It’s a Persian mille-feuilles, with dirt, rebar and concrete.
“Thickness” measures the strength of the concrete, rock, and soil in terms of concrete. In other words, how thick would a eqivalently strong structure of reinforced concrete be? The “thickness” at Natanz is probably considerably less than the actual number of meters worth of structure, rock, and soil above facility.
Generally speaking, “shallow” cut-and-cover facilities are thought to be vulnerable to the current US suite of earth penetrating munitions. The National Academies, in their report Effects of Nuclear Earth-Penetrator and Other Weapons, presents a “Summary of Precision-Guided Munitions in U.S. Family of Conventional High-Explosive Weapons, Current and Under Development…” (pp 99-102).
|Guided Bomb Unit (GBU)-28/EGBU-28/BLU-113||Air-launched, 5,000 pound, laser-guided “bunker buster” with a 4,400 pound penetrating warhead.|
|GBU-24B/D/BLU-116 Advanced Unitary Penetrator (AUP)||Air-launched, 2,000 pound, heavy steel penetrator warhead filled with high-energy explosives and void-sensing hard-target smart fuze that detonates the AUP at the optimum point in a target to inflict maximum damage.|
|BLU-118B||Thermobaric bomb, which added a thermobaric explosive fill for the BLU-109 penetrator. The BLU-118/B is a penetrating warhead filled with an advanced thermobaric explosive that, when detonated, generates higher sustained blast pressures in confined spaces such as tunnels and underground facilities. The BLU-118/B uses the same penetrator body as the standard BLU-109 weapon. The significant difference is the replacement of the high-explosive fill with a new thermobaric explosive that provides increased lethality in confined spaces.|
|Conventional Air-Launched Cruise Missile (CALCM) Block II Penetrator||Air-launched cruise missile with precision guidance and a 1,200 pound AUP penetrating warhead augmented with two forward shaped charges (BROACH concept) for use against buried and/or hardened targets.|
|Joint Standoff Weapon (JSOW)/Bomb Royal Ordnance Augmenting Charge (BROACH)||Air-launched weapon incorporating the BROACH Multiple Warhead System (MWS), combining an initial penetrator charge (warhead) with a secondary follow-through bomb, supported by multi-event hard-target fuzing. Has a 500 pound class “unitary” warhead providing blast/fragmentation effects as well as enhanced penetration capability against hard targets.|
|Tactical Missile System Penetrator (TACMS-P)||An Advanced Concept Technology Demonstration integration of the Army Tactical Missile System (ATACMS) booster with a Navy reentry vehicle, resulting in an improved capability against buried and/or hardened targets. The TACMS-P range extends to 220 km and will be compatible with the Multiple Launch Rocket System family of launchers.|
|Joint Air-to-Surface Standoff Missile (JASSM)||Conventionally armed, low-observable cruise missile with a 1,000 pound warhead optimized for penetration; it carries a new, high-yield explosive and a hard-target smart fuze. Joint Direct The JDAM will upgrade the existing inventory Attack Munition of Mk-83 1,000 and Mk-84 2,000 pound (JDAM) general-purpose unitary bombs by integrating a guidance kit consisting of an inertial navigation system/Global Positioning System guidance kit. The 1,000 pound variant of JDAM is designated the GBU-31, and the 2,000 pound version is designated the GBU-32. Hard-target penetrators|
|Tactical Tomahawk Penetrator||Tactical Tomahawk missile modified to incorporate a penetrator warhead and the hard-target smart fuze.|
Performance data about these systems is, understandably, classified. LtCol Arnold Streland, citing an Air Force Magazine article that I am in the process of procuring, suggests the GBU-28 is designed to penetrate up to 100 feet of soil or approximately 22 feet of reinforced concrete.
That jibes with a leaked DIA estimate placing the depth of penetrators at about 6 m (20 feet) of reinforced concrete and the assessment of then-Lt Col Eric M. Sepp (furthest right) …
I am not kidding, that really is Colonel Sepp. Anywho …
… in his master’s thesis for the Air War College. Sepp states explicitly what is implied in both the joint DOE/DOD Report to Congress on the Defeat of Hard and Deeply Buried Targets and the National Academies:
The “cut-and-cover” facilities are constructed by digging a hole, inserting a facility, and then covering it up with dirt and rocks. These cut-and-cover facilities can be just below the surface of the ground or may reach a depth of perhaps 100 feet, and represent the vast majority of underground facilities today. In the case of contemporary cut-and-cover facilities, there is no question that conventional munitions can defeat them.
Of course some cut and cover facilities are harder than others—Saddam’s German-built bunker beneath the Believer’s Palace seems to have survived the war in tact.
Natanz is probably not like Saddam’s bunker. Although perhaps 20 meters underground, much of the cover appears to be rock and soil. I would guess—though a structural engineer would be helpful here—that Natanz has an overburden is closer to 6 m than 20.
I note, coincidentally, that Israel is purchasing 100 GBU-28s.
One enormous weakness of Natanz is that it lacks the best defense any HDBT can have: concealment. Concealment includes both hiding the location and layout of the strcuture and inhibiting battle damage assessment to know when enough is enough. In the case of Saddam’s bunker, one defensive mechanism appeared to be “false floors” that caused GBU-28s to detonate prematurely.
Collapsing the roof, by the way, is not the option. Given the overhead imagery available, the US IC should have a very sophisticated understanding of the facility and its links to the outside world. The United States could choose to entomb the structure by collapsing entrances, ventillation systems and cutting the water and power. Centrifuge facilities like to be clean and temperature controlled, so entombing the facility would do quite a bit of damage. Anyone inside the entombed facility, slowly suffocating in the dark, would probably be praying for the roof to cave in.
If the President was feeling particularly plucky that day, he could use special forces teams to breach the facility, though I think serving as spotters is probably the most likely role.
All of this is to say that I would be surprised if a nuclear weapon were our only option in cracking this facility.