The mechanical and electrical properties of graphite and related materials such as multilayer graphene depend strongly on the presence of defects in the lattice structure, particularly those which create links between adjacent planes. We present findings which suggest the existence of a new type of defect in the graphite or graphene structure which connects adjacent planes through continuous hexagonal sp 2 bonding alone and can form through the aggregation of individual vacancy defects. The energetics and kinetics of the formation of this type of defect are investigated with atomistic density functional theory calculations. The resultant structures are then employed to simulate high resolution transmission electron microscopy images, which are compared to recent experimental images of electron irradiation damaged graphite. The rich variety of structures and topologies that result from the ways that carbon atoms can bond with each other provides us with a multitude of opportunities and challenges. A particularly important problem concerns the response of graphite to damaging radiation, especially where it forms the neutron moderator and reflector blanket in a nuclear fission reactor. In this application, it is essential for the structural integrity of the material to be maintained for decades in a harsh, inaccessible environment. The mechanical and electrical properties of graphite, as well as other forms of nanostructured carbon and graphene, can be substantially altered through irradiation [1][2][3]. In the case of graphite, irradiation (with neutrons, electrons, or ions) causes changes to electrical resistance and thermal conductance [2,4,5] and anisotropic changes to both elastic properties and the crystal dimensions, together with expansion in the prismatic direction, balanced by shrinkage in the basal plane [6,7]. These changes arise from a complex evolution of a population of point defects in the graphite structure (Frenkel pairs of lattice vacancies and self-interstitials created when impacting energetic particles displace atoms) into prismatic and basal dislocations [8] and other interstitial and vacancy aggregates [9][10][11]. The processes involved occur over many time and length scales, and the fundamental mechanisms behind the observed property changes are still unresolved, even after 70 years of intensive research.One of the most useful experimental insights into the evolution of the graphite structure under irradiation comes from high resolution transmission electron microscopy (HRTEM) images [12]. This method can resolve prismatic edge and basal dislocations in the graphite structure when viewing along the c axis (i.e., perpendicular to the planes) and the topology of individual layers and prismatic edge dislocations when viewing along the planes (side on) [13]. HRTEM images typically show evidence for the rupturing and bending of the planes [14,15] as well as dislocation climb and the growth of new planes under irradiation [16]. However, the atomistic mechanisms driving these processes are not re...