The Marine Corps Embassy Security Group (MCESG) assigns 1,500 Marine Security Guards (MSGs) to 149 embassy detachments annually. While attempting to fulfill several billet requirements, MCESG strives to balance MSG experience levels at each embassy detachment and assign MSGs to their preferred posts. The current assignment process is accomplished manually by three Marines and takes more than 6,000 hours per year. This thesis presents the Marine Security Guard Assignment Tool (MSGAT). MSGAT is an Excel-based decision support tool that utilizes a system of workbooks to guide MCESG through a streamlined data collection and provide optimal assignments. MSGAT assignments result in a higher satisfaction when compared with manual assignments. MSGAT has had an immediate and quantifiable impact on the assignment process. It has reduced person-hours by 80%, increased overall assignment quality and efficiency and improved the operational readiness of MCESG by optimizing MSG assignments.