Molecular statics and molecular dynamics (MD) simulations based on the embedded atom method (EAM) are used to model the energetics and mobility of tightly bound clusters of selfinterstitial atoms (SIA) in bcc iron. Single and clusters of SIA are directly produced in displacement cascades generated in neutron and high energy charged particle beam irradiations. The clusters are composed of <111> split dumbbells and crowdions with binding energies in excess of 1 eV. Clusters containing specified ‘magic’ numbers of SIA can be described as perfect prismatic dislocation loops with Burgers vector b=a/2<111>; however, the core region is extended compared to an isolated edge dislocation and the loops are intrinsically kinked. As the loops grow, SIA occupy successive edge rows, with minimum energy cusps found at the magic numbers corresponding to filled hexagonal shells. The SIA clusters are highly mobile, undergoing rapid one-dimensional diffusion on their glide prism. The activation energy for glide diffusion is less than 0.3 eV and the corresponding mechanism is related to easy motion of the intrinsic kinks. The kinks, which are preferentially observed on the hexagonal corners, propagate around the loop periphery, resulting in stochastic increments of glide. Image drift forces bias cluster motion near free surfaces and the consequential annihilation of clusters at the surface produces islands bounded by hexagonal ledges. The potential effect of islands modifying surface topology is also discussed. While these simulations are specific to iron, similar behavior is expected for other cubic alloys.