OTTAWA - The Conservative government's plan to build Arctic patrol ships could send some of Canada's maritime coastal defence vessels into early retirement.

Already short of sailors and struggling with budget shortfalls, the navy is working out how to crew and operate the six-to-eight new ice-capable corvettes that were announced this week by Prime Minister Stephen Harper.

"We think that these vessels are going to be the natural replacement for the (coastal defence vessels),'' Commodore Kelly Williams, vice chief of maritime staff, said Wednesday in an interview.

The $3.1-billion program to build armed Class 5 medium icebreakers to enforce Canada's northern sovereignty was announced Monday with much fanfare at Esquimalt, B.C., the navy's principle West Coast base.

An additional $4 billion will be set aside over 25 years to operate the ships.

The smaller Kingston-class coastal defence vessels, built in the 1990s by the former Liberal government at a cost of $650 million, will be "transitioned'' to a new role, Williams said.

It's still unclear what that role will be and whether the navy will have the sailors or money to keep all 12 of the 934-tonne ships. Senior naval staff met this week in Ottawa to discuss those questions.

With the first of the new Arctic ships not due until 2013 at the earliest, Williams said there is plenty of time to make decisions.

The 55-metre coastal ships, originally conceived as minesweepers, are not suitable for patrols in choppy seas beyond the immediate coastline. At a top speed of 15 knots, they're also considered slow.

Most warships have a 30- to 35-year lifespan and the Kingston-class, the last of which hit the water in 1999, are at only the mid-point in their service life.

"There's an awful lot of work that remains to be taken out of those ships,'' said Williams. "Canadians would expect us, having invested in those vessels, to use them to the maximum advantage possible.''

He said he could see them used for training and ideally would like to keep some for patrols close to the coastline, while the Arctic corvettes and frigates work farther offshore.

But a retired fleet commander said that was unlikely.

"We're in a resource-strained environment,'' said Eric Lerhe, a retired commodore and member of Dalhousie University's Centre for Foreign Policy Studies in Halifax.

"The navy would undoubtedly love to keep the (maritime coastal defence vessels). They've been a success story.''

A planned $100-million, life-extending refit for the coastal vessels has already been shelved by the navy.

Senator Colin Kenny, whose security and defence committee has recommended Canada's defence budget be increased to $25 billion by 2010, from its current $18 billion, agreed with Lerhe's assessment.

The Conservative government shows no appetite for boosting defence spending to that level, he said.

A strategic assessment, written last year and obtained by The Canadian Press under the Access to Information Act, sounded blunt warnings about the navy's future.

Among other things, it called for a massive injection of capital to upgrade existing vessels and to begin building the next generation of warships. Some of those concerns were addressed with the Arctic ships plan and the announcement that the country's 12 Halifax-class frigates will receive a $3.1 billion modernization.

But the assessment also painted a stark picture of the navy's struggle to live within its current $701-million operating budget, with the rising cost of fuel and maintenance and the departures of experienced sailors.

In early 2006, there was a shortage 276 qualified personnel, a situation that hasn't improved much in the last year, a navy official acknowledged.

With the regular navy stretched, Williams said the new icebreakers will likely be crewed by reservists.

"We really don't have a detailed answer yet for crewing concepts, but we think the naval reserves are going to play a massive role in the manning of these vessels,'' he said.

Unlike the army and the air force, which plug reservists into empty slots within existing units, the navy has a designated role for its existing 4,500 part-time sailors. They form entire ship's companies, crewing all 12 of the Kingston-class vessels.

Although Harper's government has pledged to add 13,000 reservists to the Canadian Forces, the bulk of them are destined for the army.

Asking reservists to crew the new Arctic ships will present some training challenges in terms of technology and the addition of helicopters, said Williams, but added he's confident they're up to the task.