FORT EUSTIS, Va. - A maritime enforcement specialist at Port Security Unit (PSU) 305, fires a M-203 grenade launcher training round during a four-day field evolution, May 20, 2011. PSUs provide protection to vessels in security zones and pier areas and also provide security for internal unit needs such as the command center, communications center, berthing areas entry control points (ECP), vehicle control points (VCP) and traffic control/vehicle movement.