This FM provides the doctrinal basis and the responsibilities, relationships, procedures, capabilities, constraints, and planning considerations for the conduct of engineer underwater operations throughout an area of operations (AO). Its primary purpose is to integrate engineer underwater operations into the overall sustainment and mobility engineering structure. The doctrine presented is applicable for joint interagency and multinational environments in the full spectrum of operations. Army Regulation (AR) 25-30 mandates that all Army programs and functions will use the metric system. To ensure compliance with this requirement, an English-to-metric measurement conversion chart is provided in Appendix A.