Hurricane Katrina
As of September 1, 2005, Blackwater USA  sent equipment and security forces to the 
 disaster area, including a SA-330J Puma helicopter, with the stated purpose of assisting in the evacuation of citizens from flooded areas. A later press release on Blackwater USA's web site confirms that their privately contracted forces are on the ground in New Orleans, being used to secure petrochemical facilities and provide security services for the federal government.
Blackwater mercenaries used in New Orleans