This practice establishes and defines the requirements for applying human engineering to the development and acquisition of ships and marine systems, equipment, and facilities. These requirements are applicable to all phases of development, acquisition, and testing and shall be integrated with the total system engineering and development, and test effort. It is not expected nor intended that all of the human engineering activities should be applied to every marine program or program phase. Therefore, these activities shall be tailored to meet the specific needs of each program and the milestone phase of the program within the overall life cycle. This tailoring shall be performed by the procuring activity or by the contractor or subcontractor with the assistance and approval of the procuring activity in order to impose only the essential human engineering requirements on each program. Guidance for selection of only the essential requirements is contained in Appendix X1.