DoD recognizes two levels of maintenance: Field level and Depot level maintenance. Field-level is comprised of both organizational maintenance, which includes inspections, servicing, handling, preventive and corrective maintenance, and Intermediate Maintenance, which includes assembly and disassembly beyond the capability of the organizational level. Depot-level maintenance includes any action performed on materiel or software in the conduct of inspection, repair, overhaul, or the modification or rebuild of end-items, assemblies, subassemblies, and parts. Depot level maintenance generally requires extensive industrial facilities, specialized tools and equipment, or uniquely experienced and trained personnel that are not available in lower echelon-level maintenance activities.