OTTAWA -- The commander of the Royal Canadian Navy is defending the Trudeau government's plan to spend billions of dollars on upgrading Canada's submarine fleet.

Vice-Admiral Ron Lloyd tells The Canadian Press that having a submarine is the best way to spot others that may be approaching or have even entered Canadian waters or those of NATO allies.

But Lloyd won't say whether Russia, China or any other country has been sniffing around Canadian waters, citing the need for secrecy.

Such silence is not new, but it does underscore the long-standing challenge in justifying repeated government and military assertions in Canada about the need for submarines.

Canada's four existing Victoria-class vessels, purchased from the U.K. in 1998, have a reputation for breakdowns and other problems, even though Lloyd and others say they have turned a corner.

Lloyd does note that foreign countries are building submarines faster than most other weapons, particularly Asia, where the navy has been increasing its operations amid growing regional tensions.