Top East Coast naval brass are pointing to a recent foray by a foreign power as an act of aggression that shows why Canada needs a strong sub-sea presence.

Rear-Admiral John Newton, commander of the East Coast navy, shared details of the 2015 incident during a media tour aboard HMCS Windsor, one of Canada's four submarines.

Last fall, NATO forces noticed five submarines belonging to a major foreign power moving into the North Atlantic. Newton did not name the country.

The subs — four nuclear-powered and one diesel-electric — were tracked to the area near Iceland and Greenland.

The Canadian military deployed Halifax-based HMCS Windsor, and Aurora patrol aircraft from 14 Wing Greenwood.

The response was in coordination with American and European allies to "demonstrate resolve" against this show of aggression, Newton said.

Teaching old subs new tricks

HMCS Windsor is one of four submarines purchased by the Canadian government nearly two decades ago from Britain. They were slow to be put into service, and have had numerous issues over the years including on-board fires and collisions with the sea floor.

But the subs are getting significant technological refits.

CBC reporter Brett Ruskin spent a night aboard the submarine HMCS Windsor. 1:40

HMCS Windsor is now using the same sonar system found on the United States' Virginia-class submarines, considered among the most capable nuclear subs on the planet. The sonar system can identify and track targets from many kilometres away.

Military officials showed the system to members of the media, but did not permit them to take pictures or disclose specific details about its performance capabilities.

'These submarines or no submarines'

Canada's submarines have often been criticized for being second-hand and expensive to maintain.

While both those assertions are true, the subs are still good value for money, said Ken Hansen, a retired military officer and independent maritime security analyst.

"It was these submarines or no submarines," he said. "We couldn't have bought new submarines for the money that was available [in 1998]. Therefore, we had to buy used. It was simple."

Next mission involves trip to Norway

He said the submarines are powered by diesel-electric engines, which are quieter than many nuclear-powered submarines.

Beneath the surface, HMCS Windsor runs on battery power. A nuclear submarine needs complex systems for power and heat management that produce slightly more noise.

The next mission for Canada's East Coast submarine involves a trip to Norway, followed by a series of international exercises planned to take place in the waters between Halifax and St. John's.