Which role is responsible for ensuring 100% accountability during in-processing and out-processing?

The Battalion S-1 is responsible for ensuring 100% accountability during in-processing and out-processing because this role focuses primarily on personnel management within the battalion. The S-1 serves as the human resources officer and is tasked with managing all aspects related to personnel, including tracking and accounting for service members as they enter and exit the unit. This responsibility involves coordinating the in-processing and out-processing procedures, ensuring that every soldier's records are updated and verified, and that they are accounted for according to Army regulations.

The S-1's involvement ensures that any personnel changes are documented accurately, which is crucial for maintaining readiness and ensuring that the unit is properly manned. The accountability processes are critical, especially when it comes to deployments, transfers, and other operational requirements. Therefore, the S-1 plays an essential role in the overall human resources function by keeping track of personnel transitions and maintaining complete accountability at all times.