The structure has three floors below ground. Originally only two below-ground floors were planned, but a third was added during the review process. The top two floors of the northern (E Street) structure housed the fingerprint bureau. Special features of the building included a pneumatic tube system and a conveyor belt system for handling mail and files. A special, reinforced, extra-thick "protection slab" existed beneath the second floor to help protect the building from street-level explosions. A gravel-filled dry moat ran along the building on E Street NW.