The 56-page report, "Weighing Benefits and Costs of Military Action Against Iran,"(pdf) concluded that a unilateral Israeli attack could delay Iran's nuclear programme for up to two years while a more massive U.S. assault could set it back by up to four years.
But either effort is also likely to provoke both direct and indirect retaliation by Tehran - both in the region and beyond; destroy the U.S.-led international coalition that has imposed harsh economic sanctions against Iran; and increase the country's determination to acquire a weapon.
"(A) military action involving aerial strikes, cyber attacks, covert operations, and special operations forces would destroy or severely damage many of Iran's physical facilities and stockpiles," according to the report, which was signed by three former national security advisers and two former heads of the U.S. Central Command, among others.
"But in our judgment, complete destruction of Iran's nuclear program is unlikely; and Iran would still retain the scientific capacity and the experience to start its nuclear program again if it chose to do so."
"...In fact, we believe that a U.S. attack on Iran would increase Iran's motivation to build a bomb, because 1) the Iranian leadership would become more convinced than ever that regime change is the goal of U.S. policy, and 2) building a bomb would be seen as a way to inhibit future attacks and redress the humiliation of being attacked," according to the report, which was unveiled at the Wilson International Center for Scholars here Thursday.
Described by its authors as an effort to provide "a basis for open and informed discussion of a matter of crucial importance to America's national security," it was released amidst growing tensions between Prime Minister Benjamin Netanyahu and the administration of President Barack Obama over the Israeli leader's demands that Washington lay out specific "red lines" that, if crossed by Iran, would prompt U.S. military action against Iran.
After Secretary of State Hillary Clinton rejected Netanyahu's demands last weekend, Netanyahu re-iterated warnings that, absent U.S. guarantees, Israel would act unilaterally.
"Those in the international community who refuse to put red lines before Iran," he declared Tuesday, "don't have a moral right to place a red light before Israel."
The Obama administration has made little secret of its strong opposition to a unilateral Israeli strike for many of the reasons listed in the new report.
If anything, the report will likely reinforce that opposition, particularly given the prominence of many of its signers, among them, former national security advisers Brent Scowcroft, Zbigniew Brzezinski, and Sandy Berger, and two former chiefs of the U.S. Central Command (CentCom), Gen. Anthony Zinni and Adm. William Fallon, as well as the former Deputy Commander of the U.S. Special Operations Command (SOC), Lt. Gen. Frank Kearney.
Besides Scowcroft, a former Air Force general who served as national security adviser to Presidents Gerald Ford and George H.W. Bush, other prominent Republicans included former Nebraska Sen. Chuck Hagel, former Trade Representative Carla Hills, and former Deputy Secretaries of State John Whitehead and Richard Armitage.
Others signers who served in top national-security positions under Republican presidents included former U.N. Amb. Thomas Pickering, former Undersecretary of State Nicholas Burns, former Assistant Secretary for Near East Affairs Edward Djerejian, former National Intelligence Officer for Near East and South Asia Paul Pillar, and the former ambassador to Egypt, Frank Wisner.
The report itself stressed that it was "not an advocacy document", but rather an effort to "depoliticize discussion of a highly charged issue" and provide a summary of "informed analysis and opinion" regarding key questions that should be answered before any military action is undertaken.
Shared assumptions, it noted, included the notion that a nuclear-armed Iran would "pose dangerous challenges to U.S. interests and security, as well as to the security of Israel"; that Tehran has twice sought to secretly expand its nuclear programme; and that military force should be used as a "last resort".
The report, the product of six months of discussions, concluded that if Iran decided to "dash" for a bomb - a decision that has not yet been made and that, account to the report, U.S. intelligence agencies would likely detect - Tehran would need one to four months to produce enough weapons-grade material to produce one bomb and an additional two years to build a nuclear warhead that could be reliably delivered by a missile.
"(E)xtended military strikes by the U.S. alone or in concert with Israel could destroy or severely damage the six most important known nuclear facilities in Iran, setting back Iran's nuclear program for up to four years," it found. "Our informed estimate is that a military strike by Israel alone could delay Iran's ability to build a bomb for up to two years."
If Washington's aim was to ensure that Iran never acquires a nuclear bomb, "the U.S. would need to conduct a significantly expanded air and sea war over a prolonged period of time, likely several years," it found.
"If the U.S. decided to seek a more ambitious objective, such as regime change ...or undermining Iran's influence in the region, then an even greater commitment of force would be required to occupy all or part of the country."
Such a commitment, it warned, would require more than what Washington has already "expended over the past 10 years in the Iraq and Afghanistan wars combined", according to the report.
The more-limited campaign could produce benefits beyond damaging or destroying Iran's most important nuclear facilities and much of its military capabilities, it said. It would also demonstrate U.S. "seriousness and credibility" to U.S. allies in the region, and possibly disrupt the regime's control, "although we do not believe it would lead to regime change, regime collapse, or capitulation."
It may also help deter nuclear-weapons proliferation, particularly in the region, it said.
But the costs of such an attack could be very high indeed. "While some argue that that Iran might hold back using force in order to avoid provoking a larger scale conflict, we believe that Iran would retaliate, costing American lives; damaging U.S. facilities in the region; and affecting U.S. interests in Iraq, Afghanistan, the Gulf, and elsewhere," the report noted, adding that Iran would also "hold Israel partly responsible for any attacks, whether or not Israeli forces participated in military action."
Tehran would likely act against both the U.S. and Israel indirectly, as well, using "well-armed proxies such as Hezbollah or Shiite militant groups in Iraq" to retaliate.
International support for sanctions and isolating Iran would likely break down, while an attack could also "introduce destabilizing political and economic forces in a region already experiencing major transformations," according to the report.
It also warned that unilateral U.S. action "could further alienate Muslims and others worldwide, reinforcing the view that the United States resorts too often to military force," and offering new recruitment opportunities to radical Islamist groups, including Al-Qaeda.
As for the possibility of an attack sparking regime change, "we conclude that U.S. and/or Israeli strikes are more likely to unify the population behind the government than to generate resistance," the report said.
The 56-page report, "Weighing Benefits and Costs of Military Action Against Iran,"(pdf) concluded that a unilateral Israeli attack could delay Iran's nuclear programme for up to two years while a more massive U.S. assault could set it back by up to four years.
But either effort is also likely to provoke both direct and indirect retaliation by Tehran - both in the region and beyond; destroy the U.S.-led international coalition that has imposed harsh economic sanctions against Iran; and increase the country's determination to acquire a weapon.
"(A) military action involving aerial strikes, cyber attacks, covert operations, and special operations forces would destroy or severely damage many of Iran's physical facilities and stockpiles," according to the report, which was signed by three former national security advisers and two former heads of the U.S. Central Command, among others.
"But in our judgment, complete destruction of Iran's nuclear program is unlikely; and Iran would still retain the scientific capacity and the experience to start its nuclear program again if it chose to do so."
"...In fact, we believe that a U.S. attack on Iran would increase Iran's motivation to build a bomb, because 1) the Iranian leadership would become more convinced than ever that regime change is the goal of U.S. policy, and 2) building a bomb would be seen as a way to inhibit future attacks and redress the humiliation of being attacked," according to the report, which was unveiled at the Wilson International Center for Scholars here Thursday.
Described by its authors as an effort to provide "a basis for open and informed discussion of a matter of crucial importance to America's national security," it was released amidst growing tensions between Prime Minister Benjamin Netanyahu and the administration of President Barack Obama over the Israeli leader's demands that Washington lay out specific "red lines" that, if crossed by Iran, would prompt U.S. military action against Iran.
After Secretary of State Hillary Clinton rejected Netanyahu's demands last weekend, Netanyahu re-iterated warnings that, absent U.S. guarantees, Israel would act unilaterally.
"Those in the international community who refuse to put red lines before Iran," he declared Tuesday, "don't have a moral right to place a red light before Israel."
The Obama administration has made little secret of its strong opposition to a unilateral Israeli strike for many of the reasons listed in the new report.
If anything, the report will likely reinforce that opposition, particularly given the prominence of many of its signers, among them, former national security advisers Brent Scowcroft, Zbigniew Brzezinski, and Sandy Berger, and two former chiefs of the U.S. Central Command (CentCom), Gen. Anthony Zinni and Adm. William Fallon, as well as the former Deputy Commander of the U.S. Special Operations Command (SOC), Lt. Gen. Frank Kearney.
Besides Scowcroft, a former Air Force general who served as national security adviser to Presidents Gerald Ford and George H.W. Bush, other prominent Republicans included former Nebraska Sen. Chuck Hagel, former Trade Representative Carla Hills, and former Deputy Secretaries of State John Whitehead and Richard Armitage.
Others signers who served in top national-security positions under Republican presidents included former U.N. Amb. Thomas Pickering, former Undersecretary of State Nicholas Burns, former Assistant Secretary for Near East Affairs Edward Djerejian, former National Intelligence Officer for Near East and South Asia Paul Pillar, and the former ambassador to Egypt, Frank Wisner.
The report itself stressed that it was "not an advocacy document", but rather an effort to "depoliticize discussion of a highly charged issue" and provide a summary of "informed analysis and opinion" regarding key questions that should be answered before any military action is undertaken.
Shared assumptions, it noted, included the notion that a nuclear-armed Iran would "pose dangerous challenges to U.S. interests and security, as well as to the security of Israel"; that Tehran has twice sought to secretly expand its nuclear programme; and that military force should be used as a "last resort".
The report, the product of six months of discussions, concluded that if Iran decided to "dash" for a bomb - a decision that has not yet been made and that, account to the report, U.S. intelligence agencies would likely detect - Tehran would need one to four months to produce enough weapons-grade material to produce one bomb and an additional two years to build a nuclear warhead that could be reliably delivered by a missile.
"(E)xtended military strikes by the U.S. alone or in concert with Israel could destroy or severely damage the six most important known nuclear facilities in Iran, setting back Iran's nuclear program for up to four years," it found. "Our informed estimate is that a military strike by Israel alone could delay Iran's ability to build a bomb for up to two years."
If Washington's aim was to ensure that Iran never acquires a nuclear bomb, "the U.S. would need to conduct a significantly expanded air and sea war over a prolonged period of time, likely several years," it found.
"If the U.S. decided to seek a more ambitious objective, such as regime change ...or undermining Iran's influence in the region, then an even greater commitment of force would be required to occupy all or part of the country."
Such a commitment, it warned, would require more than what Washington has already "expended over the past 10 years in the Iraq and Afghanistan wars combined", according to the report.
The more-limited campaign could produce benefits beyond damaging or destroying Iran's most important nuclear facilities and much of its military capabilities, it said. It would also demonstrate U.S. "seriousness and credibility" to U.S. allies in the region, and possibly disrupt the regime's control, "although we do not believe it would lead to regime change, regime collapse, or capitulation."
It may also help deter nuclear-weapons proliferation, particularly in the region, it said.
But the costs of such an attack could be very high indeed. "While some argue that that Iran might hold back using force in order to avoid provoking a larger scale conflict, we believe that Iran would retaliate, costing American lives; damaging U.S. facilities in the region; and affecting U.S. interests in Iraq, Afghanistan, the Gulf, and elsewhere," the report noted, adding that Iran would also "hold Israel partly responsible for any attacks, whether or not Israeli forces participated in military action."
Tehran would likely act against both the U.S. and Israel indirectly, as well, using "well-armed proxies such as Hezbollah or Shiite militant groups in Iraq" to retaliate.
International support for sanctions and isolating Iran would likely break down, while an attack could also "introduce destabilizing political and economic forces in a region already experiencing major transformations," according to the report.
It also warned that unilateral U.S. action "could further alienate Muslims and others worldwide, reinforcing the view that the United States resorts too often to military force," and offering new recruitment opportunities to radical Islamist groups, including Al-Qaeda.
As for the possibility of an attack sparking regime change, "we conclude that U.S. and/or Israeli strikes are more likely to unify the population behind the government than to generate resistance," the report said.
The 56-page report, "Weighing Benefits and Costs of Military Action Against Iran,"(pdf) concluded that a unilateral Israeli attack could delay Iran's nuclear programme for up to two years while a more massive U.S. assault could set it back by up to four years.
But either effort is also likely to provoke both direct and indirect retaliation by Tehran - both in the region and beyond; destroy the U.S.-led international coalition that has imposed harsh economic sanctions against Iran; and increase the country's determination to acquire a weapon.
"(A) military action involving aerial strikes, cyber attacks, covert operations, and special operations forces would destroy or severely damage many of Iran's physical facilities and stockpiles," according to the report, which was signed by three former national security advisers and two former heads of the U.S. Central Command, among others.
"But in our judgment, complete destruction of Iran's nuclear program is unlikely; and Iran would still retain the scientific capacity and the experience to start its nuclear program again if it chose to do so."
"...In fact, we believe that a U.S. attack on Iran would increase Iran's motivation to build a bomb, because 1) the Iranian leadership would become more convinced than ever that regime change is the goal of U.S. policy, and 2) building a bomb would be seen as a way to inhibit future attacks and redress the humiliation of being attacked," according to the report, which was unveiled at the Wilson International Center for Scholars here Thursday.
Described by its authors as an effort to provide "a basis for open and informed discussion of a matter of crucial importance to America's national security," it was released amidst growing tensions between Prime Minister Benjamin Netanyahu and the administration of President Barack Obama over the Israeli leader's demands that Washington lay out specific "red lines" that, if crossed by Iran, would prompt U.S. military action against Iran.
After Secretary of State Hillary Clinton rejected Netanyahu's demands last weekend, Netanyahu re-iterated warnings that, absent U.S. guarantees, Israel would act unilaterally.
"Those in the international community who refuse to put red lines before Iran," he declared Tuesday, "don't have a moral right to place a red light before Israel."
The Obama administration has made little secret of its strong opposition to a unilateral Israeli strike for many of the reasons listed in the new report.
If anything, the report will likely reinforce that opposition, particularly given the prominence of many of its signers, among them, former national security advisers Brent Scowcroft, Zbigniew Brzezinski, and Sandy Berger, and two former chiefs of the U.S. Central Command (CentCom), Gen. Anthony Zinni and Adm. William Fallon, as well as the former Deputy Commander of the U.S. Special Operations Command (SOC), Lt. Gen. Frank Kearney.
Besides Scowcroft, a former Air Force general who served as national security adviser to Presidents Gerald Ford and George H.W. Bush, other prominent Republicans included former Nebraska Sen. Chuck Hagel, former Trade Representative Carla Hills, and former Deputy Secretaries of State John Whitehead and Richard Armitage.
Others signers who served in top national-security positions under Republican presidents included former U.N. Amb. Thomas Pickering, former Undersecretary of State Nicholas Burns, former Assistant Secretary for Near East Affairs Edward Djerejian, former National Intelligence Officer for Near East and South Asia Paul Pillar, and the former ambassador to Egypt, Frank Wisner.
The report itself stressed that it was "not an advocacy document", but rather an effort to "depoliticize discussion of a highly charged issue" and provide a summary of "informed analysis and opinion" regarding key questions that should be answered before any military action is undertaken.
Shared assumptions, it noted, included the notion that a nuclear-armed Iran would "pose dangerous challenges to U.S. interests and security, as well as to the security of Israel"; that Tehran has twice sought to secretly expand its nuclear programme; and that military force should be used as a "last resort".
The report, the product of six months of discussions, concluded that if Iran decided to "dash" for a bomb - a decision that has not yet been made and that, account to the report, U.S. intelligence agencies would likely detect - Tehran would need one to four months to produce enough weapons-grade material to produce one bomb and an additional two years to build a nuclear warhead that could be reliably delivered by a missile.
"(E)xtended military strikes by the U.S. alone or in concert with Israel could destroy or severely damage the six most important known nuclear facilities in Iran, setting back Iran's nuclear program for up to four years," it found. "Our informed estimate is that a military strike by Israel alone could delay Iran's ability to build a bomb for up to two years."
If Washington's aim was to ensure that Iran never acquires a nuclear bomb, "the U.S. would need to conduct a significantly expanded air and sea war over a prolonged period of time, likely several years," it found.
"If the U.S. decided to seek a more ambitious objective, such as regime change ...or undermining Iran's influence in the region, then an even greater commitment of force would be required to occupy all or part of the country."
Such a commitment, it warned, would require more than what Washington has already "expended over the past 10 years in the Iraq and Afghanistan wars combined", according to the report.
The more-limited campaign could produce benefits beyond damaging or destroying Iran's most important nuclear facilities and much of its military capabilities, it said. It would also demonstrate U.S. "seriousness and credibility" to U.S. allies in the region, and possibly disrupt the regime's control, "although we do not believe it would lead to regime change, regime collapse, or capitulation."
It may also help deter nuclear-weapons proliferation, particularly in the region, it said.
But the costs of such an attack could be very high indeed. "While some argue that that Iran might hold back using force in order to avoid provoking a larger scale conflict, we believe that Iran would retaliate, costing American lives; damaging U.S. facilities in the region; and affecting U.S. interests in Iraq, Afghanistan, the Gulf, and elsewhere," the report noted, adding that Iran would also "hold Israel partly responsible for any attacks, whether or not Israeli forces participated in military action."
Tehran would likely act against both the U.S. and Israel indirectly, as well, using "well-armed proxies such as Hezbollah or Shiite militant groups in Iraq" to retaliate.
International support for sanctions and isolating Iran would likely break down, while an attack could also "introduce destabilizing political and economic forces in a region already experiencing major transformations," according to the report.
It also warned that unilateral U.S. action "could further alienate Muslims and others worldwide, reinforcing the view that the United States resorts too often to military force," and offering new recruitment opportunities to radical Islamist groups, including Al-Qaeda.
As for the possibility of an attack sparking regime change, "we conclude that U.S. and/or Israeli strikes are more likely to unify the population behind the government than to generate resistance," the report said.