The military tracks 824 installations in the Bureau of Transportation Statistics database, more than three times that number. Outfitting it with the most comprehensive layered defense would cost about $74 million, plus $5 million a year to operate, the agency estimated in a July report. Protecting 100 such sites would cost about $7.4 billion, with $500 million in annual operating costs. Staffing each site with a dedicated 66-soldier company would cost about $6.6 million a year more, CBO said. The estimates also exclude research and development, which the Pentagon funds separately at more than $300 million a year.