One of the most important but generally overlooked missions of the U.S. Navy is port security. While incidents in peacetime are generally rare, the 2000 terrorist attack on the destroyer USS Cole remains a real danger. Now the Navy is experimenting with using one of its newest unmanned boats as a way to protect warships sitting pierside from attack. In October 2000, the guided-missile destroyer USS Cole was refueling at the port of Aden in Yemen when it came under attack by Al Qaeda terrorists. A small boat loaded with explosives sidled up to the 10,000 ton destroyer and exploded, killing 17 U.S. Navy sailors and injuring 39.