Operational Test and Evaluation (OT&E) (10 USC 4171) is a fielded test, under realistic combat conditions, for a Major Defense Program (MDP) of any item or component of a weapons system, equipment, or munitions for the purposes of determining its operational effectiveness and operational suitability for combat. To ensure test adequacy, OT&E testing should only incorporate validated, accredited threat representations unless coordinated with Director, Operational Test, and Evaluation (DOT&E). [1,3]
Definition: OT&E is legally defined in USC Section 139 as the field test, under realistic combat conditions, of any item of (or key component of) weapons, equipment, or munitions for the purposes of determining the effectiveness and suitability of the weapons, equipment, or munitions for use in combat by typical military users; and the evaluation of the results of such test.
Operational Test and Evaluation (OT&E) Purpose
The purpose of OT&E is to test a system in the actual or simulated environment that it was designed for with users of the system in realistic operational conditions. This will determine if the system is operationally effective and operational suitability for combat. The OT&E provides the decision authority with an estimate of the following: 
- The degree of satisfaction of the user’s requirements is expressed as operational effectiveness and operational suitability of the new system.
- The system’s current capabilities, considering equipment already available and operational benefits or burdens associated with the new system.
- The need for further development of the new system to correct performance deficiencies.
- The adequacy of doctrine, organizations, operating techniques, tactics, and training for employment of the system; maintenance support for the system; and the system’s performance in the countermeasures environment.
Operational Test and Evaluation (OT&E) References
DoD Instruction 5000.02 lists mandatory elements of OT&E planning and execution.
Operational Test and Evaluation (OT&E) Main Evaluation Criteria
The main OT&E evaluation criteria are to determine if a system is Operationally Effective, Operationally Suitabable, and Survivable. Below is a detailed breakdown of each criteria.
- Operational Effectiveness: A measure of the overall ability of a system to accomplish a mission when used by representative personnel in the environment planned or expected for operational employment of the system considering organization, doctrine, tactics, supportability, survivability, vulnerability, and threat. 
- Operational Suitability: The degree to which a system can be placed and sustained satisfactorily in-field use with consideration being given to availability, compatibility, transportability, interoperability, reliability, wartime usage rates, maintainability, safety, human factors, habitability, manpower, logistics supportability, natural environmental effects and impacts, documentation, and training requirements. 
- Survivability: Includes the elements of susceptibility, vulnerability, and recoverability. As such, survivability is an important contributor to operational effectiveness and suitability. A survivability assessment should be conducted for all systems under OT&E oversight that may be exposed to threat weapons in a combat environment or to combat-induced conditions that may degrade capabilities, whether or not the program is designated for Live-Fire Test and Evaluation (LFT&E) oversight. 
Main Operational Test and Evaluation (OT&E) Test Activities
- Operational Assessment (OA) is an evaluation of operational effectiveness, operational suitability, and Survivability made by an independent Operational Test organization, with user support as required, on other than production systems. The focus of an OA is on significant trends noted in development efforts, programmatic voids, risk areas, adequacy of requirements, and the ability of the program to support adequate OT. An OA may be conducted at any time using technology demonstrators, prototypes, mock-ups, EDMs, or simulators but will not substitute for the IOT&E necessary to support Full-Rate Production decisions. 
- Initial Operational Test and Evaluation (IOT&E) is conducted on production, or production representative articles, to determine whether systems are operationally effective and suitable for intended use by representative users to support the decision to proceed beyond Low-Rate Initial Production (LRIP).
- Follow-on Operational Test & Evaluation (FOT&E) is the OT&E that may be necessary after the Full-Rate Production Decision Review (FRPDR) to refine the estimates made during IOT&E, evaluate changes, and reevaluate the system to ensure that it continues to meet operational needs and retains its effectiveness in a new environment or against a new threat. FOT&E is conducted during fielding/deployment and operational support and sometimes may be divided into two separate activities.
Operational Test and Evaluation Agencies
In each of the Services, operational testing is conducted under the auspices of an organization that is independent of the development agency, in environments as operationally realistic as possible, with hostile forces representative of the anticipated threat and with typical users operating and maintaining the system. Each services organization is listed below: 
- Air Force Operational Test and Evaluation Center (AFOTEC)
- Navy Commander Operational Test and Evaluation Force
- Army Test and Evaluation Command
- Marine Corps Operational Test and Evaluation Activity
- Joint Interoperability Test Command (JITC)
Operational Test and Evaluation (OT&E) Authority
Operational testing of a major defense acquisition program may not be conducted until the Director of Operational Test and Evaluation of the Department of Defense approves (in writing) the adequacy of the plans (including the projected level of funding) for operational test and evaluation to be conducted in connection with that program. The Director shall analyze the results of the operational test and evaluation conducted for each major defense acquisition program. At the conclusion of such testing, the Director shall prepare a report for the Secretary of Defense stating the completeness or incompleteness of the test. 
Where Operational Test & Evaluation is focused on determining the effectiveness, suitability, and survivability of the weapons, equipment, or munitions for use in combat by typical military users, Developmental Test & Evaluation is focused on verifying that technical performance specifications have been met with a system.
AcqLinks and References:
- DAU Defense Acquisition Guidebook (DAG) Chapter 8
- DAU Defense Acquisition Guidebook (DAG) – Test & Evaluation
- DAU Test and Evaluation Management Guide
-  DoD Test and Evaluation Management Guide
- DoD Instruction 5000.02 “Operation of the Defense Acquisition System”
- Website: Title 10 USC 4171 “Survivability testing and lethality testing required before full-scale production”
- Website: Title 10 USC 4171 “Operational Test and Evaluation of Defense Programs”
- Website: Title 10 USC 139 “Director of Operational Test and Evaluation”
- Website: The Office of the Director of Test and Evaluation (DOT&E)