During the war Mott worked on the role of plastic deformation in the progression of fracture cracks. When he returned to Bristol after the war, his having met and hired Frederick Charles Frank enabled the two of them to make considerable advances in the study of dislocations, with the help of others such as Frank Nabarro and Alan Cottrell. Bristol became an important centre of research in this topic, especially at the end of the 1940s. If Mott only produced early and somewhat minor contributions to that field, notably on alloy hardening with Nabarro and on the topology of a dislocation network lowering the apparent elastic constants of a crystal, there is no doubt that Mott's enthusiasm played its role in the three major steps forward in the field by F. C. Frank on crystal growth and plasticity and later, in Cambridge, by P. Hirsch on thin film electron microscopy.