A day after New Orleans thought it had narrowly escaped the worst of Hurricane Katrina's wrath, water broke through two levees on Tuesday and virtually submerged and isolated the city, causing incalculable destruction and rendering it uninhabitable for weeks to come.

With bridges washed out, highways converted into canals, and power and communications lines inoperable, government officials ordered everyone still remaining out of the city. Officials began planning for the evacuation of the Superdome, where about 10,000 refugees huddled in increasingly grim conditions as water and food were running out and rising water threatened the generators.

The situation was so dire that late in the day the Pentagon ordered five Navy ships and eight Navy maritime rescue teams to the Gulf Coast to bolster relief operations. It also planned to fly in Swift boat rescue teams from California.