The National Guard, with its dual federal and state roles, has been in demand to meet both overseas operations and homeland security requirements. Over the last decade the National Guard has experienced the largest activation of its forces since World War II. At the same time, the Guard’s domestic activities have expanded from routine duties, such as responding to hurricanes, to include activities such as helping to secure U.S. borders. Generally, the National Guard can operate in three different statuses: (1) state status—state funded under the command and control of the governor; (2) Title 32 status—federally funded under command and control of the governor (Title 32 forces may participate in law enforcement activities); and (3) Title 10 status—federally funded under command and control of the Secretary of Defense. Forces serving in Title 10 status are generally prohibited from direct participation in law enforcement activities, without proper statutory authorization, but may work to support civilian law enforcement. Although National Guard forces working in support of law enforcement at the southwest land border have been activated under Title 32, the Secretary of Defense has limited their activities with regard to law enforcement. Specifically, these National Guard forces are not to make arrests. Since 2006, the National Guard has supported DHS’s border security mission in the four southwest border states (California, Arizona, New Mexico, and Texas) through two missions: Operation Jump Start (June 2006-July 2008) involved volunteers from the border states and from outside the border states; its mission included aviation, engineering, and entry identification, among others, according to National Guard officials. Operation Phalanx (July 2010-September 30, 2011) involved volunteer units and in-state units. The Secretary of Defense limited the National Guard mission to entry identification, criminal analysis, and command and control, according to National Guard officials. In addition to the National Guard, DOD provided support at the southwest land border with active duty military forces operating in Title 10 status. While active duty forces are normally prohibited from direct participation in law enforcement, Congress has at times authorized it. For example, §1004 of the National Defense Authorization Act for Fiscal Year 1991, as amended, allows the Secretary of Defense to provide support for the counterdrug activities of any other department or agency of the federal government or of any state, local, or foreign law enforcement agency if certain criteria, set out in the statute, are met. Various factors influence the cost of a DOD role at the southwest land border, such as the scope and duration of the mission. Federal agency officials have cited a variety of benefits from having a DOD role at the southwest land border. The National Defense Authorization Act for Fiscal Year 2011 mandated that we examine the costs and benefits of an increased DOD role to help secure the southwest land border. This mandate directed that we report on a number of steps that could be taken that might improve security on the border, including the potential deployment of additional units, increased use of ground-based mobile surveillance systems, use of mobile patrols by military personnel, and an increased deployment of unmanned aerial systems and manned aircraft to provide surveillance of the southern land border of the United States. In September 2011, we reported that DOD estimated a total cost of about $1.35 billion for two separate border operations—Operation Jump Start and Operation Phalanx—conducted by the National Guard forces in Title 32 status from June 2006 to July 2008 and from June 2010 through September 30, 2011, respectively. Further, DOD estimated that it has cost about $10 million each year since 1989 to use active duty Title 10 forces nationwide, through its Joint Task Force-North, in support of drug law enforcement agencies with some additional operational costs borne by the military services. As we considered the various steps we were directed to address in our report, we found that the factors that may affect the cost of a DOD effort are largely determined by the legal status and the mission of military personnel being used, specifically whether personnel are responding under Title 32 or Title 10 (federal status) of the Unites States Code. For example, in considering the deployment of additional units, if National Guard forces were to be used in Title 32 status, then the factors that may impact the cost include whether in-state or out-of-state personnel are used, the number of personnel, duration of the mission, ratio of officers to enlisted personnel, and equipment and transportation needs. The costs of National Guard forces working at the border in Title 32 status can also be impacted by specific missions. For example, DOD officials told us that if National Guardsmen were assigned a mission to conduct mobile patrols, then they would be required to work in pairs and would only be able to perform part of the mission (i.e., to identify persons of interest). They would then have to contact the Border Patrol to make possible arrests or seizures because the Secretary of Defense has precluded National Guardsmen from making arrests or seizures during border security missions. Border Patrol agents, however, may individually conduct the full range of these activities, thus making the use of Border Patrol agents for these activities more efficient. At the time of our review, Title 10 active duty military forces were being used for missions on the border, and cost factors were limited primarily to situations whereby DOD may provide military support to law enforcement agencies for counternarcotic operations. Support can include direct funding, military personnel, and equipment. With the estimated $10 million that DOD spends each year for Title 10 active duty forces in support of drug law enforcement agencies nationwide, DOD is able— through its Joint Task Force-North—to support approximately 80 of about 400 requests per year for law enforcement assistance. These funds have been used for activities in support of law enforcement such as operations, engineering support, and mobile training teams. For example, DOD was able to provide some funding for DOD engineering units that constructed roads at the border. While DOD provided the manpower and equipment, CBP provided the materials. In addition, DOD was able to provide some funding for DOD units that provided operational support (e.g., ground based mobile surveillance unit) to law enforcement missions. We also reported on the cost factors related to deploying manned aircraft and unmanned aerial systems. DOD officials did not report any use of unmanned aerial systems for border security missions because these systems were deployed abroad. DOD officials, however, did provide us with cost factors for the Predator and Reaper unmanned aerial systems. Specifically, in fiscal year 2011, the DOD Comptroller reported that a Predator and a Reaper cost $859 and $1,456 per flight hour, respectively. DOD uses maintenance costs, asset utilization costs, and military personnel costs to calculate these figures. In addition, DOD officials identified other factors that may impact operating costs of unmanned aerial systems, including transportation for personnel and equipment, rental or lease for hanger space, and mission requirements. With regard to manned aircraft, DOD provided cost factors for a Blackhawk helicopter and a C-12 aircraft, which were comparable to the type of rotary and fixed-wing aircraft used by DHS. For example, in fiscal year 2011, DOD reported that a Blackhawk helicopter and a C-12 aircraft cost $5,897 and $1,370 per flight hour, respectively. DOD uses maintenance costs, asset utilization costs, and military personnel costs to develop their flight hour estimates. Furthermore, according to DOD officials, in fiscal year 2011, DOD contracted for a Cessna aircraft with a forward-looking infrared sensor (known as the Big Miguel Program), which costs $1.2 million per year and assisted at the southwest land border. Federal officials cited a variety of benefits from a DOD role to help secure the southwest land border. For example, DOD assistance has (1) provided a bridge or augmentation until newly hired Border Patrol agents are trained and deployed to the border; (2) provided training opportunities for military personnel in a geographic environment similar to combat theaters abroad; (3) contributed to apprehensions and seizures made by Border Patrol along the border; (4) deterred illegal activity at the border; (5) built relationships with law enforcement agencies; and (6) maintained and strengthened military-to-military relationships with forces from Mexico. Specifically with regard to Operation Jump Start (June 2006-July 2008), CBP officials reported that the National Guard assisted in the apprehension of 186,814 undocumented aliens, and in the seizure of 316,364 pounds of marijuana, among other categories of assistance, including rescues of persons in distress and the seizure of illicit currency. Based on these reported figures, the National Guard assisted in 11.7 percent of all undocumented alien apprehensions and 9.4 percent of all marijuana seized on the southwest land border. During the National Guard’s Operation Phalanx (July 2010-June 30, 2011), CBP reported that as of May 31, 2011, the National Guard assisted in the apprehension of 17,887 undocumented aliens and the seizure of 56,342 pounds of marijuana. Based on these reported figures, the National Guard assisted in 5.9 percent of all undocumented alien apprehensions and 2.6 percent of all marijuana seized on the southwest land border. In fiscal year 2010, active duty military forces (Title 10), through Joint Task Force-North, conducted 79 missions with 842 DOD personnel in support of law enforcement and assisted in the seizure of about 17,935 pounds of marijuana, assisted in the apprehension of 3,865 undocumented aliens, and constructed 17.26 miles of road, according to DOD officials. With regard to unmanned aerial systems at the time of our report, DOD had fewer systems available, since they were deployed to missions abroad, including operations in Afghanistan, Iraq, and elsewhere.