The United States Navy operates 23 frigates around the globe that provide critical defense functions such as protecting shipping. This mission of protecting merchant vessels dates back to the earliest American naval efforts off the Barbary Coast of Africa. President Thomas Jefferson ordered the expansion of the Navy's role to include protecting shipping after demands for tribute payments by Barbary States increased. In addition to shipping protection, frigates conduct antisubmarine operations for convoys and amphibious forces, and carry short-range anti-aircraft weapons, making them a cost-effective surface combat vessel.