In conventional warfare, support forces such as military police, engineers, and medical personnel normally operate behind the front lines of a battlefield. But in Iraq and Afghanistan–both in U.S. Central Command’s (CENTCOM) area of responsibility–there is no clear distinction between front lines and rear areas, and support forces are sometimes exposed to hostile fire without help from combat arms units. The House report to the National Defense Authorization Act for fiscal year 2010 directed GAO to report on combat skills training for support forces. GAO assessed the extent to which (1) Army and Marine Corps support forces are completing required combat skills training; (2) the services and CENTCOM have information to validate completion of required training; and (3) the services have used lessons learned to adjust combat skills training for support forces. To do so, GAO analyzed current training requirements, documentation of training completion, and lessons learned guidance; observed support force training; and interviewed headquarters officials, trainers, and trainees between August 2009 and February 2010.Army and Marine Corps support forces undergo significant combat skills training, but additional actions could help clarify CENTCOM’s training requirements, ensure the services fully incorporate those requirements into their training requirements, and improve the consistency of training that is being conducted. CENTCOM has issued a list of training tasks to be completed, in addition to the services’ training requirements, before deploying to its area of operations. However, there is confusion over which forces the CENTCOM requirements apply to, the conditions under which the tasks are to be trained, and the standards for successfully completing the training. As a result, interpretations of the requirements vary and some trainees receive detailed, hands-on training for a particular task while others simply observe a demonstration of the task. In addition, while the Army and Marine Corps are training their forces on most of CENTCOM’s required tasks, servicemembers are not being trained on some required tasks prior to deploying. While units collect information on the completion of training tasks, additional actions would help higher level decision-makers assess the readiness of deploying units and servicemembers. Currently, both CENTCOM and the services lack complete information on the extent to which Army and Marine Corps support forces are completing required combat skills training. The Army has recently designated the Digital Training Management System as its system of record for tracking the completion of required training, but guidance concerning system implementation is unclear and the system lacks some needed capabilities. As a result, support forces are not fully utilizing the system, and are inconsistently tracking completion of individual and unit training using paper records, stand-alone spreadsheets, and other automated systems. The Marine Corps also uses inconsistent approaches to document training completion. Furthermore, as GAO reported in May 2008, CENTCOM does not have a clearly defined waiver process to provide visibility over the extent to which personnel are deploying to its area of operations without having completed its required training tasks. As a result, CENTCOM and the services have limited visibility over the extent to which servicemembers have or have not completed all required training. While trainers at Army and Marine Corps training sites have applied lessons learned information and made significant changes to the combat skills training they provide support forces, the changes to training have varied across sites. Army and Marine Corps doctrine requires the collection of after action reports, the primary formal vehicle for collecting lessons learned. Lessons are also shared informally, such as through communication between deployed forces and units training to replace them. While the services have these formal and informal means to facilitate the sharing of lessons learned information, trainers at the various training sites are not consistently sharing information about the changes they have made to their training programs. As a result, servicemembers are trained inconsistently and units that are deploying for similar missions sometimes receive different types and amounts of training.