On September 11, 2001, four commercial airliners were hijacked by al-Qaeda terrorists. American Airlines Flight 11 and United Airlines Flight 175 crashed into the North and South Towers of the World Trade Center, respectively. Approximately 17 minutes separated the two impacts. Nearly 3,000 people died as a result of the attacks, which also included crashing another plane into the Pentagon and a fourth plane crashing in Shanksville, Pennsylvania. It was the deadliest terrorist attack on U.S. soil since Pearl Harbor.