Secret societies have existed for millennia; their purposes myriad. Generally, they are exclusive and require members to take an oath to keep their organization and activities secret. They possess guarded means of identification and communication. Some exist in the open, their purposes known, their activities undisclosed, and their practitioners anonymous. The US Army Security Agency was a separate organization within the Army having its own installations, training, academic, logistic, communications and scientific institutions and members took an oath to keep the organization and its activities secret, their identity and communications guarded. Until the advent of the Vietnam War, their purpose was intelligence gathering for national strategic objectives. As the US role expanded from advisory to active combat, intelligence support to combat units changed the structure and character of the Agency. Organizational secrecy, guarded communications, and member anonymity remained. The 265th Radio Research Company (Airborne) sentinels operated in the shadows, yet stood beside their warrior counterpart providing intelligence to the 101st Airborne Division. 101st Airborne units involved in the war are etched in the stone of their memorial at Arlington Cemetery. The 265th RRC (ABN), the only unit etched on the back, remains in the shadows. Nearly forty years have passed since the last Sentinel departed Vietnam. This is their story.