Skill deterioration and retraining needed to support mobilization were determined for Individual Ready Reservists (IRRs) in 16 critical Navy ratings. Mailed questionnaire were used to obtain job performance information (tasks performed and proficiency associated with their performance) from IRRs and active duty personnel. Skill deterioration was determined by differences in proficiency reported by IRRs for two different points in time: when they were separated from active service and at the time they completed the questionnaire. Retraining needs were derived by comparing IRR estimates of their current proficiency on job tasks within their rating to the same type of estimates made by current active duty personnel. Study results indicated that skills previously acquired on active duty deteriorate during the time personnel are assigned to the IRRs. Much less deterioration occurred for individuals who work in civilian jobs related to their Navy rating. For most of the ratings, the current proficiency levels of IRRs compared favorably with the proficiency levels reported by individuals currently on active duty. It appeared that the typical IRR should be able to perform most job tasks of his/her rating at mobilization after brief familiarization such as would be provided by direct, corrective supervision. (Appendixes, which form the bulk of the document, include job descriptions, cover letters, and study results for 16 ratings.) More than 100 data tables are contained in the document. (Author/YLB)