Immediately after the first attack, the captains and crews of a large number of local boats steamed into the attack zone to assist in evacuation. These ships had responded by a request from the US Coast Guard to help evacuate those stranded on Manhattan Island. Others, such as the John J. Harvey, provided supplies and water, which became urgently needed after the Towers’ collapse severed downtown water mains.

Estimates of the number of people evacuated by water from Lower Manhattan that day in the eight-hour period following the attacks range from 500,000 to 1,000,000. Norman Mineta, Secretary of Transportation during the attacks, called the efforts “the largest maritime evacuation conducted in the United States.” The evacuation was the largest maritime evacuation in history by most estimates, passing the nine-day evacuation of Dunkirk during World War II. As many as 2,000 people injured in the attacks were evacuated by this means.