US teams of special forces going into Iraq after a three-year gap will face an aggressive insurgency, a splintering military and a precarious political situation as they help Iraqi security forces improve their ability to battle Sunni militants.
The Army Green Berets, who are expected to make up much of the US force, have been assessing and training other militaries for decades as a core part of their job.
But while much of what they will be doing in Iraq will be familiar, it will be complicated by the stunning collapse of the Iraqi military, left leaderless by internal Sunni-Shiite divisions.
Experts suggest that while the elite commandos may be able to stop the immediate deterioration of Iraqi forces, it will require a far broader effort to quell the deep sectarian divide in the country and put systems in place to build more professional military leadership.
The US and Iraq on Monday reached a key agreement on legal protections that will enable up to 300 special operations forces to deploy in the country.
Two teams of 12 members each are already in Iraq and could begin their assessment this week, and another four teams are expected to go into the country soon.
"They will be very good at improving the immediate tactical proficiency of some of the Iraqi military, but they will be less prepared to address the long term heath of the Iraqi army," said retired Lt. Gen. James Dubik, who was in charge of training Iraqi forces in 2007 and 2008.
In essence, he said, the US teams will be "sharpening the tip of the spear, but not replacing the rotted staff with a new one."
In a string of battlefield victories, the Sunni militants have captured several key towns in the north and on the border with Syria and Jordan, sending Iraqi troops fleeing. Abandoned by military leaders who may have felt alienated by the Shiite-led government, troops ran, leaving their weapons and equipment.
"It's a rapidly deteriorating situation," said Rick Nelson, a senior associate at the Center for Strategic and International Studies.
"It's a hot war. They have to get in and help stop the bleeding to get the Iraqi forces to be able to maintain stability and security in the country."
Brig. Gen. Darsie Rogers, head of Army Special Forces Command, said Green Berets currently are conducting training missions in 30 countries and do so in more than 150 nations each year. Highly trained in special warfare and counterinsurgency, the teams routinely are used to help other countries build and improve their militaries.
The latest Iraq mission, Rogers said, is more akin to what special forces have been doing in Afghanistan and in the Philippines and what they did in Iraq during the war years. But it's a bit larger than similar missions going on around the world, including a number of countries in Africa.
Rogers, who served in Iraq, said the assessment phase will be important in determining how to go forward, but, "having some experience with that, I think that we will rather quickly understand where we need to apply our assistance."
The teams will determine how the US can best help the Iraqi forces, then the additional teams will deploy. They are expected to help the Iraqis improve their military systems and commands, but not embed with the fighting units or engage in direct combat.
Rogers also noted that a number of US special forces have served in Iraq.
"The relationships that we have with the Iraqis, at least those that I had while I was there, were very strong, and I'm sure that we'll be able to capitalize on this as we go back in," Rogers said.
Still, Dubik said that while the commandos will provide important short-term help for the Iraq forces, they will not be sufficient to solve the problem.
Instead, he said Prime Minister Nouri al-Maliki needs to make several critical political moves, including disbanding the office of the commander in chief, which has been blamed for roiling sectarian divisions and pushing a Shiite agenda.
US officials are also pressing for a government transition that will better empower the minorities and bring the country together, thus conceivably avoiding a civil war.
The legal agreement signed Monday was needed to get the special forces into Iraq.
The Pentagon spokesman, Rear Adm. John Kirby, said Iraq had outlined acceptable legal assurances for the short-term mission in a diplomatic note ensuring that troops will not be subject to Iraq's judicial process.
Instead, if there are any problems, troops would be subject to the US Uniform Code of Military Justice.
The legal protections are similar to those provided to US diplomats and troops working out of the embassy, officials said,
White House spokesman Josh Earnest drew a distinction between the current situation and the administration's desire to have the Iraqi parliament approve immunity for American troops when the US was looking to leave a residual force behind in 2011.
Iraq refused to sign that agreement and the US withdrew all but a small number of forces from the country in December 2011. Less than 200 troops, largely providing security, have remained at the US Embassy as part of the Office of Security Cooperation.
"We're dealing with an emergency situation - that's the first part - and there is an urgent need for these advisers to be able to do their work on the ground in Iraq," Earnest said, adding that they are going in at the request of the Iraqi government.
Officials also noted that the force being sent in now is much smaller than the several thousand that the military planned to leave there after 2011.