Montreal Trudeau Airport opened in 1941 at Dorval, at the western end of the island of Montreal. It replaced the older Saint Hubert airport across the river. Montreal was then the busiest city in Canadian aviation. Dorval soon became Canada's busiest airport and the base of Trans Canada Air Lines, later renamed Air Canada. Through the postwar decades it was the country's main gateway across the Atlantic.
Its story took an odd turn in 1975. The federal government opened Mirabel, a huge new airport far northwest of the city, meant to replace Dorval entirely. International flights were forced there, but the site was too remote and the promised rail link was never built. Airlines and travelers had to cope with two sites at once. Splitting the city that way proved deeply unpopular, and traffic drained away.
International flights began returning to Dorval in 1997. Mirabel ended scheduled passenger service in 2004 and now handles only cargo and aircraft manufacturing. Dorval was renamed for former prime minister Pierre Elliott Trudeau that same year. It is now Air Canada's second largest hub, meaning a place the airline uses to connect passengers, and the base of Air Transat. Its links to France are unusually strong.