If you've ever found yourself wondering exactly which appropriations are most appropriate to develop specific product support capabilities early in a system life cycle, encourage you to take a good look at the excellent DoD Operating & Support (O&S) Cost Management Guidebook issued by the Office of the Assistant Secretary of Defense for Sustainment. In addition to a wealth of information on all things O&S, specifically recommend taking a look at both Paragraph 2.1.2 “Appropriation Categories” and Appendix B “Mapping among IPS Elements, O&S Cost Categories, and Funding Appropriations”.