Transmission electron microscopy (TEM) observation of irradiated ferritic materials reveals the existence of large, interstitial dislocation loops with Burgers vectors ½ 〈111〉 and 〈100〉. These loops cause hardening of the material by pinning dislocations and impeding their glide during deformation. However, numerous molecular dynamics simulations of collision cascades in α-Fe have evidenced the exclusive formation of small, highly mobile, ½ 〈111〉 clusters. Additionally, continuum dislocation theory and atomistic simulations have shown that ½ 〈111〉 loops are energetically favored. This introduces the need to explain the mechanisms of formation and growth of 〈100〉 loops from small, cascade-produced clusters. The understanding of the physics underlying these phenomena is important for the development of solid damage accumulation models in ferritic materials that are being considered for fusion applications. In this work we propose a comprehensive set of dislocation reactions that explain the nucleation of 〈100〉 loops from ½ 〈111〉 clusters. The growth up to TEM visible sizes of 〈100〉 loops through absorption of one-dimensionally migrating ½ 〈111〉 clusters is also assessed. Finally, a direct comparison of TEM experimental micrographs with atomistic simulation-derived images is presented to show an example of how to help close the gap that exists between modeling and experiments.