Length of previous service, quality of relevant training, and previous job performance are most likely specifications for a _________ personnel.

The most appropriate term to describe specifications like length of previous service, quality of relevant training, and previous job performance is "trained" personnel. This designation emphasizes the importance of the skills and competencies that an employee has developed through formal or informal training experiences.

In many organizations, particularly in roles that require specific technical skills or professional expertise, the term "trained personnel" indicates individuals who have received relevant education and training that prepare them to perform in their roles effectively. Their previous job performance and the quality of their training are significant indicators of their ability to undertake the responsibilities of the current position successfully.

While "experienced" could also be a descriptive term, it typically focuses more on the duration of employment in similar roles rather than the comprehensive training aspects combined with performance metrics. Other options like "supervised" and "permanent" do not adequately convey the emphasis on training and prior accomplishments. Thus, "trained" accurately reflects the qualifications and readiness of personnel based on the criteria provided.