Israeli leaders threaten to attack Iran’s atomic weapons facilities within the next nine months before Tehran enters the “immunity zone” to then build a bomb.  But it might already be too late for Israel operating alone to inflict severe damage on Iran’s atomic weapons program.

Last week Israel’s defense minister Ehud Barak coined the term “immunity zone” to refer to the point when Iran’s atomic weapons know-how, raw materials, experience and equipment are heavily fortified in deep bunkers, immune from an Israeli attack.  That means Israel must stop Iran this year before it gains atomic weapons or accept a nuclear armed enemy. 

There is consensus among western intelligence agencies and recent evidence from the United Nation’s nuclear watchdog agency, the International Atomic Energy Agency (IAEA), that Iran has all the ingredients to build an atomic weapon.  But there is no evidence, according to Secretary of Defense Leon Panetta, Iran’s supreme leader, Ayatollah Ali Khamene’i, has given the go-ahead to build an atomic bomb. 

But waiting to discover the go-ahead order from the secretive leader is rejected by the Israelis who view an atomic-armed Iran an existential threat.  They are also losing patience with the American-led effort to coax nukes from Iran using yet another round of sanctions.

Last week, Defense Minister Barak declared time was running out on Iran’s nuclear advance and by inference the West’s sanctions.  “Whoever says ‘later’ may find that later is too late,” Barak told the Jerusalem Post.  Barak and other Israeli leaders have waited long enough; they are stoking calls for military action.

Israeli attack plans are secret, but Secretary Panetta told a Washington Post columnist it could happen between this April and June.   So, if Israel does launch an attack, what challenges does it face and how successful might it be?  

First, Israel must select enough of the right targets that, if damaged or destroyed, might slow or stop Iran’s weapons program.  But identifying atomic weapons targets can be difficult especially when your intelligence is weak in tough countries like Iran.  For example, North Korea, another tough place and partner to Iran’s nuclear development, surprised the world last fall when it unveiled a previously secret enrichment facility. 

Israel has imperfect knowledge about Iranian atomic facilities, especially those with a weapons nexus.  But the following sites are likely on her target list.

Esfahan is a uranium conversion facility 210 miles south of Tehran.  The above ground facility converts raw material into uranium gas which is then shipped to the Natanz facility for enrichment.  The complex includes an extensive tunnel complex which could house more sensitive uranium activities.  

Natanz is an enrichment facility 140 miles southeast of Tehran.  It is buried under 25 meters of earth with a 2.5-meter thick concrete ceiling and houses at least 8,000 centrifuges which have turned out enough material for several nuclear warheads. The complex includes three large underground buildings, two of which are designed to be cascade halls to hold 50,000 centrifuges.

Fordow is an enrichment facility 90 miles southwest of Tehran.  The previously secret facility is buried 80 meters inside a mountain and protected by anti-aircraft weapons.  Recently uranium fuel arrived for further enrichment.  The facility is large and safe enough from attack to provide for quick weapons grade enrichment.

Arak is a heavy water production plant 120 miles southwest of Tehran.  The above ground plant once operational could produce about 9 kilograms of plutonium annually or enough for about two nuclear weapons.

Bushehr is an above ground 1,000-megawatt reactor 500 miles from Tehran.  The fuel from this facility is sufficient to produce 50 to 75 bombs.

Parchin is a high explosives testing site 19 miles southeast of Tehran.  Last week, the IAEA was denied the opportunity to visit Parchin. The inspectors believe Parchin houses a containment vessel used to conduct tests of the high explosives used in triggering a fissile reaction.

Mojdeh is the center for weapons development located on the Ministry of Defense’s Malek-Ashtar University of Technology in Esfahan.  It works on the trigger for an atomic bomb, casting and machining of uranium metals, research on fissile material needed for a bomb, high explosives and radiation detection. 

Abyek is a formerly top secret nuclear site 75 miles west of Tehran.  The facility which was exposed by the National Council of Resistance of Iran is inside a mountain and has three large halls, 20 by 200 meters, and 100 meters below the mountain surface.  It is one of the newest command centers under the direction of Mojdeh.

It is noteworthy that in 2010 Tehran announced plans to build 10 additional enrichment sites inside mountains beginning in March 2011.  It appears Abyek is the first of those sites.

Second, these targets vary in vulnerability.  The above ground unfortified facilities are easy targets for standoff cruise missiles but the hard and deeply buried targets (HDBT) are especially challenging.

Israel has hundreds of U.S.-made bunker-buster bombs for HDBT, which might breech the cavity containing some of Iran’s buried facilities.  The GBU-27 can penetrate 2.4 meters of concrete and the GBU-28 can penetrate 6 meters of concrete and another layer of earth 30 meters deep.   Last week, the Washington, DC-based Bipartisan Policy Center’s National Security Project called for providing Israel 200 GBU-31 bombs, which include the Boeing Co. GPS tail-kit, to increase the credibility of a strike.

An article in Israel’s Tablet magazine naively suggested Israel might attack HDBT sites like Fordow with a series of bunker busters, dropped at the same point to burrow through the granite.  Same point bombing with GPS tail-kits might be possible, but identifying which parts of a massive underground facility to strike is nearly impossible without extraordinary intelligence, such as blueprints. 

Also, successfully striking an HDBT depends on fuze settings.  Accurate fuzing depends on knowing with great accuracy the types of cover, such as the PSI of the concrete, types of layering, and depth.  The most accurate fuzes rely on delays, and the delay settings are determined by the time it takes for the weapon to travel from impact to the area of detonation, the underground room housing the centrifuges.  Too long a delay and you have a hole in the wrong place.

Third, reaching Iranian targets without being detected will be a significant challenge.  Israeli aircraft must fly over unfriendly skies past much improved Iranian air defenses, bomb and escape before Iranian surface-to-air missiles challenge them.  Expect some aircraft losses.

Two flight routes appear politically possible.  Israel could cross through Syria into Iraq, which has no air defense, and then enter Iran.  Alternatively, the aircraft could pass along the Syria-Turkey border, and then cut across Iraq into Iran.  Israel would jam communications and computers along the route to avoid detection.

Israeli pilots face three significant challenges: reaching their target, delivering their ordnance on target, and returning home before running out of fuel.  Fortunately, many of Israel’s 83 F-15 fighter bombers are outfitted with extra fuel pods that have a demonstrated range of up to 1,600 miles, but they also have a limited payload capacity for heavy bunker buster bombs.  And Tel Aviv to Tehran is 1,000 miles, which means Israel’s seven refueling planes will be kept busy depending on how many F-15s and F-16s join the fight.

Jerusalem has other means than bomb-ladened fighters to destroy Iranian targets such as Popeye cruise missiles launched from Israeli Dolphin submarines and Jericho ballistic missiles armed with conventional or nuclear warheads.   Special Forces should supplement air and sea platforms to ensure mission accomplishment.

Israel’s attack challenges are extraordinary.  It is possible to conduct a strike before Iran reaches the “immunity zone,” and it would probably destroy some of Iran’s capability.  But based on the above challenges, especially insufficient intelligence on the facilities, any conventional strike by Israel working alone will be of limited value.