This minimum counterterrorism footprint requires basic stability near our long-term bases to have any effect. The ANSF must sustain that stability but can only do so supported by U.S. advisers and enablers. Advising the three Afghan National Army corps and Afghan National Police zones around the bases requires at least three advise-and-assist brigades — one per corps and zone — plus support units. Such brigades are smaller than combat brigades, about 1,500 each. They must, in this concept, be located with our counterterrorism forces to avoid having to secure additional bases.
Now we’re up to around 21,500 troops total, without a central headquarters near Kabul or any reliable means of moving by road between our bases. In the real world, neither of those conditions makes sense. Adding up the security forces for a base near Kabul, a theater headquarters, route-clearance packages, theater logisticians and other ancillary units is likely to push the requirement above 30,000.