Interviews with the party leaders this week on CBC's The National revealed a sharp difference of opinion about Canada's military role in fighting ISIS in Iraq and Syria.

Canada joined the U.S.-led coalition to combat ISIS, also known as Islamic State or ISIL, last year. The mission, Operation Impact, includes six CF-18s, an aerial refueller, two surveillance planes and about 600 personnel involved in the air war, as well as 69 special forces training Kurdish fighters.

The three leaders who have participated so far in Peter Mansbridge's interviews have laid out dramatically different directions for the future of Canada's military mission in Iraq and Syria. (Canadian Press)

The commitment could run until the end of March. Defence Minister Jason Kenney revealed last April that the total cost for the mission could top $528 million, in incremental costs over the Defence Department's regular expenses to maintain the Armed Forces.

The interviews got our military-watchers talking.

Mulcair: Withdraw from Iraq

"We will immediately withdraw our troops from Iraq," NDP Leader Tom Mulcair told CBC News chief correspondent Peter Mansbridge on Wednesday when asked what he would do if elected prime minister in October.

NDP Leader Tom Mulcair sits down for an exclusive interview with Peter Mansbridge. 32:46

"And to the extent that they are doing some bombing in Syria, and from Syria," he added.

"I think that the best thing for Canada to do is to start playing a positive role for peace, and that would be a top priority for me as the prime minister of Canada," Mulcair said.

George Petrolekas, a retired colonel, sees withdrawal as a possible credibility issue for Canada among international partners.

"If we came up to another crisis, could Canada be depended on to join a coalition of the willing?" he said. "They will question, at least, in the future, our credibility as an ally."

Retired colonel Michel Drapeau agrees the allies might not be too pleased with a pullout, but he also sees some merit to it.

"I find it a bold, but courageous decision by Mulcair," he said, adding that he views Canada's military contribution as "symbolic more than anything else."

Drapeau said he would like to see a public debate about the efficacy of Canada's contribution, and that the future discussion should focus on the ground battle — which he said will be essential in the region.

"I might have done the same decision if I were in his position," Drapeau said. "If nothing else, to open up the opinion and debate on ground troops."

Harper: Stay the course

Conservative Leader Stephen Harper's position is to maintain the military mission.

Prime Minister Stephen Harper sits down with Peter Mansbridge for an exclusive interview. 26:21

"It remains important, even with the deficiency of the ground forces in the region, that we keep this organization [ISIS] on the defensive," said Harper on Monday in his interview with Mansbridge.

"So we're in for the long haul?" asked Mansbridge.

"We have to be in for the long haul," said Harper.

Petrolekas suggests that could mean five to 10 years.

"I don't think that's what Canada is signing up for," he said.

But Drapeau sees Harper getting the benefit of supporters who want Canada to stay the course in the battle against ISIS.

"But our contribution is limited in scope and not a solution in itself," Drapeau said.

"If Harper wants to go to bed every night and say we are doing our share, well, I don't think we are," he said. "The response is minuscule in proportion to the threat he describes."

Trudeau: Train local troops

On Tuesday, Liberal Leader Justin Trudeau told Mansbridge: "We have to be part of the training of the local troops on the ground in order to carry the fight effectively against ISIS."

Liberal Leader Justin Trudeau sits down with Peter Mansbridge for an exclusive interview. 30:03

His position is a bit facile, said Drapeau.

"There is no professional army engaged there to train," said Drapeau. "They don't need training, they need the political will from others [NATO or other Mideast troops] to say I will commit a brigade or two [on the ground]."