The Coast Guard crew of a Port Security Unit (PSU) assigned to a "Raider" boat prepares to board a fishing vessel in the Persian Gulf during Operation Desert Storm in 1991. These units developed roots during the World Wars, safeguarding the nation's waterways and ports. It was during Vietnam, however, where the concept of deployable PSUs, staffed by drilling reservists, was born. Though the reservists only trained together annually, they could be called upon to assemble their unit and deploy immediately when the need dictated, as evidenced by Operations Desert Storm, Desert Shield and Iraqi Freedom. Currently, there are six permanent PSUs, staffed by reservists as well as a cadre of active duty personnel.