Process by which components or systems are tested and the results evaluated to assess progress of design, performance, supportability, etc. There are three types of T&E -- Development (DT&E), Operational (OT&E), and Production Acceptance (PAT&E)-- occurring during the acquisition cycle. DT&E is conducted to assist the engineering design and development process, to proof manufacturing processes and control and to verify attainment of technical performance specifications and objectives. OT&E is conducted to estimate a system's operational effectiveness and suitability, identify needed modifications, and provide information on tactics, doctrine, organization, and personnel requirements. PAT&E is conducted on production items to demonstrate that those items meet the requirements and specifications of the procuring contracts or agreements. OT&E is further subdivided into two phases--Initial Operational (IOT&E) and Follow-on Operational (FOT&E). IOT&E must be conducted before the production decision (Milestone III) to provide a credible estimate of operational effectiveness and suitability. Therefore, IOT&E is a field test conducted on a production representative system in an operationally realistic environment, by typical user personnel and includes use of realistic threats. FOT&E is conducted on the production system to verify operational effectiveness and suitability, to fill data voids from the IOT&E, or to verify correction of deficiencies in materiel, training, or concepts.