What event initiated the mobilization of over 20,000 Navy reservists post-9/11?

The event that initiated the mobilization of over 20,000 Navy reservists post-9/11 was Operation Noble Eagle. This operation was launched in response to the terrorist attacks on September 11, 2001, and its primary focus was to enhance U.S. domestic security measures, including the protection of critical infrastructure, airports, and military bases. It marked the beginning of increased military readiness and engagement in homeland defense activities following the attacks.

While other operations mentioned, such as Operation Desert Storm, Operation Iraqi Freedom, and Operation Desert Shield, relate to military actions in the Persian Gulf and the broader Middle East, they occurred in different contexts and timelines, particularly before 9/11 or were part of ongoing military engagements rather than direct responses to the September 11 attacks. Therefore, Operation Noble Eagle is specifically aligned with the immediate response to the events of that day and illustrates the shift in military focus to homeland security and readiness against potential threats.