Every U.S. ship has the necessary connections to connect to land-based power grids. Normally these are used to draw power into the ship, but they can be made t

Every U.S. ship has the necessary connections to connect to land-based power grids. Normally these are used to draw power into the ship, but they can be made to work both ways. Even non-nuclear ships can push power, at least until they run out of fuel. The big problem is that the power grid is usually deavily damaged by the disaster (or non-existent to begin with in some countries), so there's nothing for the ship(s) to hook up to. Even without tying up at the pier to push power, an aircraft carrier or large amphibious ship can provide tremendous support: desalinization plants capable of producing thousands of gallons of fresh water each day, helicopters capable of conducting search and rescue and/or transporting relief supplies, doctors and corpsmen trained in field medicine, command and control aircraft to tame all of the chaos listed above, etc.