Who conducts the training for upgrading an operator's license?

The correct answer, licensed operators, conducts the training for upgrading an operator's license. This is because licensed operators possess the necessary experience and knowledge to instruct others on the specific requirements and skills needed to effectively operate a vehicle or equipment safely. Their hands-on expertise allows them to provide practical training, ensuring that trainees can apply learned skills in real-world scenarios.

In this context, unit commanders, medical personnel, and investigation officers play roles in other areas such as oversight, health assessments, and inquiries, respectively. They do not specialize in the instructional aspect of training or upgrading an operator's license, making their involvement in this specific training process less relevant. Therefore, it is the licensed operators who are best suited to provide this training due to their demonstrated competence and expertise in the field.