What day were the largest number of Americans killed?

The largest number of Americans killed in a single day occurred on September 11, 2001, during the terrorist attacks when nearly 3,000 people lost their lives. The attacks involved the hijacking of four commercial airplanes, with two crashing into the World Trade Center in New York City, one into the Pentagon, and the fourth, United Airlines Flight 93, crashing in Pennsylvania after passengers attempted to retake control from the hijackers. This tragic event marked a significant moment in U.S. history, leading to widespread changes in national security and foreign policy.