Which manual covers sentinel and command and control subsystems crew drill training?

The correct answer is found in TC 44-646-15, which specifically addresses the training requirements and procedures for the Sentinel and command and control subsystems. This training circular provides detailed guidance on drills, operations, and the integration of these systems, ensuring that crew members are adequately prepared to perform their roles in air defense operations.

This manual is crucial for familiarizing personnel with the functionalities and the intricacies of the equipment they will handle, thus enhancing operational readiness and the effectiveness of air defense management.

In contrast, other options such as FM 3-01 and ATP 3-99.5 cover broader topics related to air defense operations and tactics but do not focus specifically on crew drills for the Sentinel systems. AR 750-1 primarily pertains to the maintenance management of Army equipment rather than operational training drills. This distinction highlights why TC 44-646-15 is the most suitable reference for the specific training needs outlined in the question.