having grown up in the segregated education system and culture then prevalent in the United States, McNair advocated for separate battalions of African American soldiers, arguing that they could be more effectively employed in this manner. In McNair's construct, such units could be deployed for functions including guarding lines of communication in rear areas and near front lines, or maintained as a reserve by division and corps commanders and committed where they were most needed during combat. The proposal that was adopted was closer to what McNair had advocated, and the AGF lengthened the initial training period. African American officers generally filled company grade positions as they completed OCS, with white officers holding the field grade and senior command positions. In cases where there were not enough African Americans, white officers filled the company grade positions as well. Anti-tank weapons and doctrine Developing and employing anti-tank weapons and creating suitable doctrine proved to be an ongoing challenge, for which some historians have faulted McNair. Marshall favored creation of self-propelled anti-tank weapons; McNair had long favored towed weapons, including the M3 gun. McNair recognized the limitations of the anti-tank weapons then available, and favored a defensive approach for their use, advocating that units emplace and camouflage them, but official doctrine called for a more offensive mindset. It also called for anti-tank units to conduct independent operations; McNair favored a combined arms approach. He believed the use of anti-tank weapons was an economical and efficient means to defeat enemy tanks, and would free up U.S. tanks for wider offensive operations. When the M3 anti-tank gun proved to be a less than optimum anti-tank weapon, the Army began development of tank destroyers – self-propelled tracked vehicles with a gun capable of engaging a tank, but which were faster and more maneuverable because they had thinner armor than a tank. When it appeared that the Infantry and Cavalry branch chiefs might subsume proposed tank destroyer units into their own task organizations, Marshall attempted to continue progress on tank destroyer development without generating active dissent by approving creation of the Tank Destroyer Center at Camp Hood. In practice, the separate Tank Destroyer Center meant that commanders of armor and infantry units had little or no experience with anti-tank weapons, or the most effective way to employ them. After having initially fielded the anti-tank weapon it had available – the M3 towed gun – the Army