Fiber optic assemblies and cables having subunits with a security feature

One embodiment is a fiber optic cable including at least one subunit, a tube, a plurality of strength members, and a cable jacket. The subunit includes a fiber optic ribbon and a sheath, wherein the sheath is tight-buffered about the fiber optic ribbon, thereby inhibiting buckling of the ribbon during temperature variations. The tube houses at least a portion of the at least one subunit to form a tube assembly. The plurality of strength members are disposed radially outward of the tube and are surrounded by the cable jacket. Other embodiments include a plurality of subunits in a stack with each subunit having a sheath for security purposes. Additionally, a tube assembly can have a fiber optic packing density of about 0.05 or greater.