The federal government says it remains committed to its plan to withdraw the country's fighter jets from the Middle East, but Canada's former chief of defence staff says the reasoning behind that decision continues to be unclear.

"I haven't heard the clear articulation yet of why we would bring home those CF-18s," retired general Rick Hillier told Chris Hall on CBC Radio's The House, just one day after Canadian special forces trainers and two CF-18s took part in a counteroffensive against ISIS in northern Iraq.

"Our government will make that decision based on a certain set of rules, criteria and circumstances — I haven't heard those," Hillier said.

"I think what happened [in Iraq] underscores the fact that this entire military mission of the overall strategy against [ISIS] is under-resourced. More resources are needed in the military fight, not less."

Despite Defence Minister Harjit Sajjan saying the latest attack doesn't constitute "combat" in Canada's assist and advise role, but is rather a case of "evolving tactics," Hillier said boots on the ground means combat can't always be avoided.

"You may be there to train, but as circumstances are not always controlled by you, you may end up in combat, and clearly that's what happened," he said.

"When you're in a war zone — where the enemy has a vote, as we always say — you don't know if you're going to be in and out of combat."

Canada's former top soldier has made the case for continuing airstrikes in Syria and Iraq before, and doubled down on his belief that a two-pronged strategy consisting of air strikes and trainers would be most effective in the mission against ISIS.

"Both things have to occur if you're going to help defeat ISIS and remove that blot on humanity," Hillier said.

"You have to help build up the Kurdish defence force, the Iraqi defence forces and hopefully some of the moderate Syrian groups, because if you can't build them up, you're going to be engaged there forever, and that's what no Western power wants."

Hillier wouldn't say how many Canadian special forces trainers he thinks are required, but said it would have to be more than the current 69.

"Certainly there'd be a lot more than 69 required, that's for sure, if you're going to have an effective impact."

'Leaner' military

But with Justin Trudeau promising in this month's Throne speech to invest in building a "leaner" military, Hillier isn't so sure what's realistic when it comes to Canada's role in the international coalition against ISIS.

"I'm not sure what 'leaner' means," he said.

"What I'm hoping it means is we're going to do a defence review and come up with a white paper [government policy outline] that says here's the Canadian Forces we're going to have and that we need going forward, as part of a Canadian strategy of how we shape ourselves in the world."

Hillier pointed out that the last review was in 2008 and is "overdue" for an update that would look ahead to the next 20 to 25 years.

100 days to start fulfilling promises

Hillier, who commanded the NATO-led mission in Afghanistan, also discussed the issue of veteran care.

With post-traumatic stress disorder rates nearly tripling amongst veterans in the last eight years, as well as "significantly higher" suicide rates among army troops who were deployed to Afghanistan, veteran mental health care is a pressing concern for the new government.

"They've got a really tough job in front of them, because there's been a perception amongst many veterans that they've been abandoned by their country, and that perception's going to be hard to change," Hillier said of the government's next steps in fulfilling campaign promises to vets.

"Delivering those programs is going to be absolutely key," he said, adding that he would like to see the New Veterans Charter, implemented in 2006, overhauled and "in a public manner."

"The government has started well, they have the confidence, I believe, right now of many of the veterans, but that confidence will continue only when they see actions," Hillier said.

Hillier gave the Liberals a timeline of 100 days before veterans' confidence will start to wane.

"I think you've probably got 100 days or so — that's the traditional time frame — and if you're not delivering hard on those programs by then, then you're going to start to create the same impression that the government before had.

"So the veterans I know and talk to are feeling positive, and they're looking for the actions. That's what they're waiting for."