That's the Coast Guard's mission. FEMA's mission was, in the plan, to provide follow on support for evacuees. They were leaning forward and had provisions, and people (including non government people like the Red Cross, in position to do that. Not as close as one might have liked, but until the storm hit, they couldn't risk having those pre positioned people and provisions taken out by the storm itself. The Coast Guard is by it's nature more mobile than fleets of SUVs and 18 wheelers. IIRC, the Air Force (out of Eglin) and Navy, off the Bataan, were on scene about the same time as the Coast Guard, and the National Guard helicopters. But all those were mostly doing rescue work, not bringing in supplies or ground forces. That was the plan. The National Guard had at least 300 troops on site before the storm hit, along with provisions to allow the folks in the superdome to ride out the storm. However those people were not supposed to be in the Superdome beyond the next day, so the provisions for longer than say two days, were not there.
The mayor, by not deploying the buses as per the plan, and remember the superdome and other areas were high and dry until Wednesday, screwed the pooch. Then there was the other little problem of rescue helicopters being fired upon from the area of the 'dome, and of the buses being rushed by mobs which scared the drivers off in many cases.
"The Coast Guard is by it's nature more mobile than fleets of SUVs and 18 wheelers. IIRC, the Air Force (out of Eglin) and Navy, off the Bataan, were on scene about the same time as the Coast Guard, and the National Guard helicopters. But all those were mostly doing rescue work, not bringing in supplies or ground forces. That was the plan."
Not really - one convoy of army or marine trucks can carry alot more relief than a helo. Mobility is not only speed but also mass .