For the first time since 1817, U.S. Coast Guard vessels on the Great Lakes are being outfitted with weapons – machine-guns capable of firing 600 bullets a minute.

Until now, coast guard officers have been armed with handguns and rifles, but the vessels themselves haven't been equipped with weapons.

The War of 1812 saw violent battles on Lake Erie and Lake Huron between U.S. troops and British forces, which were largely composed of militias from Britain's colonies in what is now Canada. After the war, the United States and Britain – and later Canada – agreed to demilitarize the Great Lakes waters.

The Rush-Bagot Treaty of 1817 allowed each country to station four vessels, each equipped with an 18-pound cannon, to safeguard the Great Lakes.

The antiquated treaty has recently been reinterpreted because of U.S. concerns about customs violations, human smuggling and international terrorism.

Live-fire drills conducted near Sault Ste. Marie, Ont.

Each vessel is now equipped with a 7.62-mm machine-gun, a light military gun that is the same calibre as a deer rifle but capable of shooting 600 bullets per minute.

The guns are typically mounted because of their weight. But a spokesman for the U.S. Coast Guard, Petty Officer William Colclough, said they will be stored below decks on the coast guard's 11 Great Lakes cutters and will be mounted only when needed.

Warning shots will be fired when vessels refuse to stop, said Colclough, who is based at the U.S. Coast Guard's Great Lakes headquarters in Cleveland.

Colclough said staff members have conducted live-fire drills in the past few months in American waters off the coast of Sault Ste. Marie, Ont.

Can carry high-calibre guns that can down a helicopter

A Canadian Foreign Affairs official said Ottawa has agreed to read the treaty in such a way that coast guard vessels may be mounted with guns by considering them weapons of law enforcement rather than war.

Canada reserves the right to arm its own vessels as well, the official told CBC News.

Under the reinterpretation, which both sides say honours the spirit of the original treaty, vessels may be outfitted with machine-guns of sizes up to .50-calibre. That would be big enough to bring down a helicopter and shoot through a light-armoured vehicle

Colclough said the United States has no intention of equipping the vessels with .50-calibre machine-guns at this point.

Frederick Stonehouse, a Michigan-based historian who has written 26 books on the Great Lakes, said the Rush-Bagot treaty's references to wooden ships and cannons have long been obsolete.

However, Stonehouse said the spirit of the treaty remains both clear and respected by both sides.

"Certainly the Great Lakes [have] not had any military vessels stationed on [them] since – gosh, really since the advent of that treaty."