While there are a few guards wandering about at the Mark Center, many officials are concerned over the relative lack of security at the facility. Fueling that concern is an internal Pentagon blast study of the impact of a truck bomb on the Mark Center, a copy of which TIME has obtained. The study was conducted, using a series of plausible scenarios given the layout of the facility, because vehicles can drive right up unimpeded from a number of angles.

The studies explore the hypothetical impact of truck bombs ranging from 1,000 lb. to 20,000 lb. parked at various easily accessible Mark Center locations. Officials chose the bomb sizes to match the explosive punch of bombs used in various high-profile terrorist attacks, including Oklahoma City, Beirut in 1983, Khobar Towers in 1996 and Nairobi in 1998, among others.

Several of the studies show the Mark Center would essentially be wiped out.