US:As Iran and the US continue to talk tough, the military option is being talked of increasingly in Washington. Tom Clonanexamines how it might be exercised.
As the UN-imposed deadline on Security Council Resolution 1737 passes today, diplomatic efforts will intensify to end Iran's nuclear programme.
If such efforts fail US diplomatic sources are stating that a fall-back military option is being actively prepared to destroy Iranian nuclear facilities at Natanz, Isfahan, Arak and Bushehr.
US Central Command (Centcom) has in recent weeks prepared detailed operational orders for the destruction of hundreds of military and related targets across Iraq if President Mahmoud Ahmadinejad fails to bow to international pressure to suspend Iran's uranium enrichment activities.
Today's deadline is but one of a series of critical phases identified by the US and Israel in Iran's attempts to enrich uranium at its Natanz nuclear site close to Tehran.
US sources already believe that the Atomic Energy Organisation of Iran (AEOI) has succeeded in assembling two or three cascades - each consisting of 164 gas centrifuges - at Natanz. Based on progress to date, it is believed the Iranians have the capability to install up to 3,000 such centrifuges at Natanz - enough to begin industrial scale uranium enrichment - by mid-June.
Described as Iran's point of no return by the Israeli authorities, this development would mean that by the summer the Iranians would be in a position to effectively generate low-grade enriched uranium for energy purposes or high-grade enriched uranium for an Iranian nuclear weapon.
In a highly significant development, in tandem with Centcom's military planning, the US has recently deployed two aircraft carrier strike groups to the Persian Gulf. The USS John C Stennis and USS Dwight D Eisenhower strike groups each have up to 90 combat aircraft at their disposal to begin air attacks and cruise missile strikes on targets throughout Iran.
In the event of such air and missile strikes on Iranian targets, Centcom's first task would be to strip out Iran's air defence and air force assets prior to pinpoint attacks on its nuclear facilities.
While US ground forces are experiencing overstretch in Iraq, its significant air and naval assets in the Gulf region would be more than capable of decimating Iran's ageing air force, naval and missile defences.
Such a campaign would probably take no more than 72 hours or so, with minimal US losses.
To this end the US has included in its inventory of weapons in the Persian Gulf thousands of Tomahawk cruise missiles and Trident fleet ballistic missiles aboard its aircraft, surface vessels and submarines.
Critically, the US has also deployed hundreds of massive BLU-109 Penetrator so-called bunker buster bombs, along with BLU-119 Crash Pad bunker-busting munitions designed to penetrate and destroy hardened underground structures such as those at Natanz and Isfahan.
Having suppressed Iran's air defences, the US strategy would be to follow up these attacks with air-launched BLU-109s and BLU-119s from US B-2 Stealth bombers or F/A 18 long range fighter-bombers.
The BLU-109 Penetrator is designed to penetrate more than three metres of reinforced steel and concrete, along with up to 35 metres of packed earth and soil.
US and Israeli intelligence sources believe that the vulnerable centrifuges and cascades the Iranians have located at Natanz are buried just 25 metres below ground and are protected by approximately two metres of reinforced concrete - in theory placing them within range of US warheads.
Significantly, the Israeli Defence Forces have recently acquired hundreds of these BLU-109 and BLU-119 weapons from the US.
Their long range fighter-bombers have also recently been modified to make the return flight from Israel to Tehran possible.
Israel's recent acquisition of GBU-31 JDAM (Guided Bomb Unit Joint Direct Attack Munitions) conversion kits for their aircraft make the delivery and successful deployment of these mission-specific munitions not just possible, but highly feasible.
In a parallel development, Israel's strategic 69th Air Force Squadron, along with the Tol Hof Squadron, have undergone intensive training in long-range missions involving bunker buster and tactical nuclear weapons in recent weeks.
Dr Tom Clonan is The Irish Times security analyst. He lectures in the School of Media, DIT.