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Two famous veterans of Vietnam - a POW pilot and a wounded infantryman - sparred over U.S. policy in Iraq as President Obama's nominee for Defense Secretary to lead the U.S. out of Afghanistan sought confirmation Thursday.

Sen. John McCain told former Sen. Chuck Hagel he was on "the wrong side of history" where it comes to the 2007 surge of American troops into Iraq. It's a six year-old debate, but McCain was flying in the face of public opinion when he and President Bush pushed to add more American boots on the ground in Iraq.

Hagel, then a Republican Senator, broke ranks with his party to publicly criticize the move.

McCain and Hagel's military careers could not have been more different. McCain was the Naval Academy educated son of a famous Navy family. Hagel was called in by the draft board in 1967 and then volunteered for service. McCain was shot down over Vietnam and spent seven years as a POW. Hagel spent one year in Vietnam, but he was wounded twice in battle. He would be the first former enlisted service member to head the Pentagon. The service of both men is beyond reproach.

But their policy differences were on vivid display as McCain, who Hagel supported for president in 2000 but not in 2008, stared across the Senate hearing room at his old colleague and demanded "yes or no" answers that Hagel refused to give. Hagel said he stood by the comments, "because I made them," but he said whether he was right to oppose the surge and a matter for history to judge.

The recent history would suggest the surge did help stabilize the Iraqi government and along other factors like the so-called " Sunni awakening" where former insurgents turned their guns on al Qaeda kick-started a security turnaround in the country. The last U.S. combat troops left Iraq in 2011.

"Our concerns pertain to the quality of your professional judgment and the - your worldview on critical areas of national security, including security in the Middle East," McCain told Hagel at the outset of his questioning. McCain pointed first to comments Hagel made in 2006 that a surge was a dangerous foreign policy and moved on to other moments where Hagel criticized putting more American troops into Iraq.

Their exchange was tense. Here is just a portion:

Sen. MCCAIN: "I want to know if you were right or wrong. That's a direct question. I expect a direct answer.

MR. HAGEL: The surge assisted in the objective. But if we review the record a little bit -

SEN. MCCAIN: Will you please answer the question? Were you correct or incorrect when you said that the surge would be the most dangerous foreign policy blunder in this country since Vietnam? Were you correct or incorrect?

MR. HAGEL: My -

SEN. MCCAIN: Yes or no?

MR. HAGEL: My reference to the surge being both dangerous -

SEN. MCCAIN: Are you going to answer the question, Senator Hagel? The question is, were you right or wrong? That's a pretty straightforward question.

MR. HAGEL: Well -

SEN. MCCAIN: I will - I would like to answer whether you were right or wrong, and then you are free to elaborate.

MR. HAGEL: Well, I'm not going to give you a yes or no answer on a lot of things today.

SEN. MCCAIN: Well, let the record show that you refused to answer that question.

McCain, who paid a political price for his support of the surge; it arguably cost him the presidency, later added that Hagel was on the wrong side of history about the surge. Hagel had a position similar to that of many Democrats, including President Obama, Vice President Biden and Sen. John Kerry and others currently in the administration. But McCain saved the tough questioning on this issue for Hagel.

"I think history has already made a judgment about the surge, sir, and you're on the wrong side of it. And your refusal to answer whether you were right or wrong about is going to have an impact on my judgment as to whether vote for your confirmation or not. I hope you will reconsider the fact that you refused to answer a fundamental question about an issue that took the lives of thousands of young Americans," said McCain.

Sen. Bill Nelson, D-Fla., defended Hagel a moment later, arguing that the intelligence that led to the war in the first place placed all the people on the wrong side of history.

"Since the issue of Iraq has come up here, I just want to state for the record and lay the predicate that this senator was one of many that voted for the authorization to go into Iraq, and as it turns out, the lessons of history, we were given incorrect information as a justification for going into Iraq. We were told by the secretary of defense, by the secretary of state, by the national security adviser and the director of the CIA that there were weapons of mass destruction in Iraq. And so for a lot of the decisions that were made at the outset, they were decisions that were informed with incorrect information," said Nelson.

Later Hagel gave a more thoughtful answer to McCain when he was asked by Nelson about his service in Vietnam. He argued that the guiding principle in all of his public service has to do with the troops.

"In my 12 years in the Senate, my one guiding principle on every security decision I made and every vote I cast was always this, simply this: Is our policy worthy of our troops and their families and the sacrifices that we ask them to make?," he asked.

Hagel argued it is that principle and his time as an enlisted infantryman that led him to opposed the Iraq surge.

I know it's easy here - it is anywhere - if you don't have a connection to some of this, to see these things a little differently. It doesn't mean I'm any better, Senator. It doesn't mean I'm any smarter, doesn't mean I am any more appreciative of the service to our country. That's not it. I saw it from the bottom. I see what - I saw what happens. I saw the consequences and the suffering and the horror of war.

I always ask the question, is this going to be worth the sacrifice, because there will be sacrifice. In the surge case in Iraq, we lost almost 1,200 dead Americans during that surge, and thousands of wounded. Now, was it required? Was it necessary? Senator McCain has his own opinion on that, shared by others. I'm not sure. I'm not that certain that it was required. Now, it doesn't mean I'm right, doesn't mean I didn't make wrong votes. But that's what guides me.

When you ask me the question about my time in Vietnam and was I wounded, well, I was a very insignificant part of this. We were just doing our job, Senator, as every military person knows that. Some of this committee has rather distinguished members who served, starting with Senator McCain and the sacrifices he's made to this country. But it does condition you.

I'm not shaped, framed, molded, consumed by that experience. Of course not. But it's part of me. I tried to explain that in my opening statement. We're all shaped by those experiences. I hope that experience that I've had is for the better. I hope that if I have the privilege of serving as secretary of defense, it will put someone in charge at the Pentagon - not questioning past secretaries of defense; I can only speak for myself - who understands the realities of consequences of war. Doesn't mean I'm better, but that's who I am. I don't walk away from that. I acknowledge that. But it doesn't consume me, Senator.