For service of over 180 consecutive days at a site designated as isolated, remote, insular or constituting a hardship. See CCPM, Subchapter CC27.1, INST 1 for qualifying sites. - Ready Reserve officers are eligible if an aggregate of 180 days are served within a 3-year period. - State Department 'post differential' used for foreign sites. - Officers assigned to ships classified as 'Unusually Ardous Sea Duty,' e.g., absence from home port exceeds 180 days.