Bragg coherent X-ray diffraction imaging (BCDI) is a powerful means of operando materials characterization at the nanoscale. With the ability to measure 3D structure and strain in materials at few nm resolution and under real-world conditions, BCDI has provided unique insight into a variety of materials processes. We apply BCDI to directly image the 3D structural and strain field evolution in copper nanoparticles corroding in saline solution. We observe a defect driven, anisotropic corrosion process that is accompanied by nanoscale pit formation and lattice strain variation. To understand the origin of these phenomena, we build experimentally informed atomistic models of the corrosion process. Figure 1