The Operations and Support (O&S) Phase is where a system is used and supported by users in the field. The main focus of this phase is the execution of a support system that sustains the system in the most cost-effective manner possible. The second main focus of this phase is the disposal of a system when it has reached its useful life. See Disposal.
A major focus during the sustainment effort of the Operations and Support (O&S) Phase is identifying root causes and resolutions for safety and critical readiness degrading issues. These efforts include participating in Trade Studies and decision-making relative to changes to the product support package, process improvements, modifications, upgrades, and future increments of the system. All these changes need to consider the operational needs and the remaining expected service life, Interoperability or technology improvements, parts or manufacturing obsolescence, aging aircraft (or system) issues, premature failures, changes in fuel or lubricants, and Joint or service commonality.
Disposal and Demilitarization
The final phase of the Acquisition Process is the Disposal and Demilitarization Phase. A system or piece of equipment is decommissioned when a system has reached its useful life due to age, economic feasibly, new technology, or outdated capabilities. These systems range from real estate, weapons, aircraft, ships, computers, and much more.
It has to be disposed of in accordance with legal and regulatory requirements and policy relating to safety (including explosives safety), security, and the environment, in accordance with the PSS. Disposal planning should be considered early in the design lifecycle of any system.
Disposal Cost should also be consist of the expenses associated with demilitarization and disposal of a system at the end of its useful life. Typically costs include: 
- Collection/storage/disposal of hazardous materials and/or waste
- Materials processing
- Safety precautions
- Transportation of the system to and from the disposal site
The Operations and Support (O&S) Phase should produce: (See Milestone Requirements Matrix)
- Input to Capability Development Document (CDD) for next increment
- Modifications and upgrades to fielded systems
- System Safety Analyses to include Environmental, Safety, Occupational and Health (ESOH) risk analysis, sustaining hazard analyses for the fielded system, and input to the next increment
- Data for next In-Service Review
- Programmatic Environment, Safety, and Occupational Health Evaluation
- Periodic updates to maintenance procedures through Reliability Centered Maintenance Analysis
- Compliance Schedule for National Environmental Policy Act (NEPA) (as required)
- Updated Systems Engineering Plan (SEP)
The Major Review during the Operations and Support (O&S) Phase:
AcqLinks & References:
- Defense Acquisition Guidebook (DAG) – Chapter 1
- Milestone Requirements Matrix
- DoD Instruction 5000.02 “Operation of the Defense Acquisition System”
- DoD Directive 5000.01 “Defense Acquisition System”