Photo: Canadian Forces

The head of the navy says the country needs submarines to know what is happening beneath the waves around Canada — though he won't say if foreign subs are actually poking around Canadian waters.

The Trudeau government's new defence policy includes a plan to extend the lives of the navy's four submarines so they can sail into the 2030s, which sources say will cost upwards of $2.5 billion.

Vice-Admiral Ron Lloyd says that investment is necessary, as having a submarine is the best way to spot others that may be approaching or have even entered Canadian waters, or those of its NATO allies.

"It's just like airspace. You want to know what's operating in your airspace. You want to know what's approaching your airspace. You want to know what's taking place in your airspace," he said in an interview.

"If you want to know where submarines are operating, when they're operating, how they're operating, submarines allow you the opportunity."

He said the fact that foreign countries are building submarines faster than most other weapons, particularly in Asia, only underscores their recognized importance by militaries around the world.

But Lloyd won't say whether Russia, China or any other country have actually been operating in or around Canadian waters, or those of its closest allies, citing the need for secrecy.