Gen. Martin Dempsey also touched on his concerns about the spread of the Ebola virus and what's more to come in the coalition battle against murderous Islamic extremists.
ISIS has inched closer to the Iraqi capital Baghdad this week and continued fighting in strategically important Anbar Province.
"I don't see that happening," he said. "I'm confident we can assist the Iraqis to keep Baghdad from falling."
However, Iraqi forces, some of whom abandoned their posts when ISIS began its assault on Iraq, need more training, Dempsey said. Still, they have "established a fairly formidable defensive perimeter around Baghdad" that Dempsey characterized as "a very thick and deep defense."
Dempsey repeated what he said before Congress weeks ago,
stressing that doesn't see a need to put troops on the ground in the fight against ISIS. He was firm on the controversial notion that American troops could once again head back into Iraq to fight after being involved in a conflict that stretched from 2003 to 2011
And yet he also told CNN that "war is discovery" and that if the situation evolves to the point where ground troops are necessary, he will evaluate that and make recommendations to President Barack Obama.
There are 12 teams of military advisers in Iraq now, he said.
Dempsey said the U.S. got a "significant commitment" from other members of the international coalition to add advisory teams. Dempsey said the plan is to set up three bases where the U.S. and others can train Iraqi security forces who are battling ISIS on the ground, along with Kurdish fighting forces.
He then reiterated that "war is discovery," stressed that ISIS is a "national security threat" and said that airstrikes alone will not beat ISIS though they have forced the group to change "the way it's moving."
Fighting ISIS is going to take "patience," Dempsey said, so it's critical that the U.S. and the coalition show progress soon.
For now, "we're on the right path."
Dempsey also revealed that the international coalition's operation against ISIS has a name: "Inherent Resolve."
The name, to him, means that "we need to be able to be credible and sustainable over time in order to accomplish the mission that we've been given."
'We gave Iraq a chance'
The chairman put much of the blame for the growth of ISIS on the Iraqi government.
Despite airstrikes and international outrage, the terror group is overrunning Iraqi forces and making significant strides in Syria.
"We gave Iraq a chance -- an opportunity," Dempsey said, talking about the war. "They failed to take that opportunity."
"The coaching, and teaching, and mentoring, the thousands of interactions at the local level were all wasted by the government of Iraq that chose deliberately to follow a sectarian agenda and alienate entire segments of the population, which created an environment in which ISIL could return and could flourish," he said, using an alternative acronym for ISIS.
When asked who in the U.S. government underestimated ISIS, Dempsey said: "I think what we all probably missed was the degree to which the Iraqi armed forces had eroded and wouldn't stand and face ISIL. I think we all missed that."
Dempsey alarmed about Ebola months ago
The chairman said he has been concerned about Ebola as a global threat for at least 90 days.
"I'm worried about it because we know so little about (Ebola)," he said, adding that his worry is stoked by seemingly conflicting information about how the virus can be spread.
The Centers for Disease Control and Prevention has said that the deadly virus, which originated in Africa, can be passed only through direct contact with bodily fluids when a person suffering from it exhibits symptoms.
"If you bring two doctors who happen to have that specialty into a room, one will say, 'No there is no way it will ever become airborne, but it could mutate so it could be harder to discover,' " and another might say something completely different, Dempsey said.
He said he is alarmed by the World Health Organization's warning that Ebola cases could increase and the virus could mutate.
"Then it will be an extraordinarily serious problem," he said. "I don't know who is right. I don't want to take that chance, so I am taking it very seriously."