How to destroy a hard drive in five seconds

You are on a U.S. military aircraft, transporting hard drives with important, classified information, when you collide with another plane and are forced to land near an enemy intelligence agency. There is no time to delete the files, and the drives are in heavy-duty steel cases so that they are difficult to destroy. You have a few minutes before someone finds you, grabs the drives, and searches them for even the smallest trace of useful data. What would you do?