Correspondence issued by the Government Accountability Office with an abstract that begins "In order to satisfy the requirement in the Ike Skelton National Defense Authorization Act for Fiscal Year 2011 to report on the security of the southwest land border of the United States, we briefed Congress on July 12, 2011, with our preliminary observations. This is our final report to Congress on the Department of Defense (DOD) issues we addressed in response to the mandate. As directed by the mandate, we assessed: (1) what is known about the costs and benefits of an increased DOD role to help achieve operational control over the southwest land border, including the deployment of additional units, the National Guard, or other DOD personnel; increased use of ground-based mobile surveillance systems by military personnel; and use of additional mobile patrols by military personnel, particularly in rural, high-trafficked areas; and (2) what is known about the costs and benefits of an increased deployment of additional unmanned aerial systems and manned aircraft to provide surveillance; as well as the impact of any increased deployment of unmanned aerial systems or manned aircraft on national airspace use and availability.."