What was Canada's response to September 11, 2001?

Canada offered immediate solidarity and military support to the United States after the September 11, 2001 al-Qaeda terrorist attacks that killed about 2,977 people. Canada's response included Operation Yellow Ribbon (the diversion of 226 inbound transatlantic flights to 17 Canadian airports on September 11), commitment to NATO's Article 5 collective-defence response (activated September 12, 2001 for the first time in NATO's history), and the deployment of Canadian Forces to Afghanistan from October 2001. The 9/11 attacks transformed Canadian foreign and security policy.

Canada's immediate response was led by Prime Minister Jean Chrétien. The federal government ordered the closure of Canadian airspace to commercial traffic on September 11, 2001 (Operation Yellow Ribbon) and accepted 226 diverted transatlantic flights carrying about 33,000 passengers and crew. The largest diversions went to Halifax, Nova Scotia (47 flights), Vancouver International (39 flights), and Gander, Newfoundland (38 flights). Gander, with a population of about 10,000, hosted about 6,600 stranded passengers for several days, an episode dramatised in the Broadway musical 'Come from Away' (premiered 2017). Several thousand additional passengers were diverted to Stephenville, St. John's, Goose Bay, Moncton, Toronto, and other airports.

Canada participated in the immediate diplomatic and military response. The Canadian Embassy in Washington became a major hub of the diplomatic response. Chrétien spoke to President George W. Bush by telephone on September 11. The federal Parliament held a rare emergency session on September 17, 2001. Canada committed to NATO's Article 5 invocation on September 12, 2001 (NATO's first invocation in its history; ratified by all members on October 4, 2001 once the perpetrators were identified).

Operation Apollo (Canada's contribution to the US-led intervention in Afghanistan) began October 7, 2001. Canadian special forces (JTF2) and a Royal Canadian Navy task group in the Arabian Sea were the initial deployments. The Canadian Princess Patricia's Canadian Light Infantry Battle Group deployed to Kandahar in January 2002. Operation Apollo continued until October 2003. Operation Athena (Canada's contribution to the NATO International Security Assistance Force ISAF in Afghanistan) ran from August 2003 to March 2014. About 40,000 Canadians served in Afghanistan; 159 Canadian Forces members and 7 Canadian civilians died in the conflict. Canada also deployed about 950 personnel in Operation Frustrate (the embargo on Iraq) from 1991 to 2003, but Chrétien declined to commit Canadian forces to the 2003 Iraq War. Canadian airport security was transformed (creation of the Canadian Air Transport Security Authority in 2002), and federal anti-terrorism law was substantially strengthened (Bill C-36 Anti-Terrorism Act, December 2001).