This thesis focuses on potential tactical uses of Quick Response (QR) codes for optical signaling. It examines visual communications methods used effectively by the fleet throughout history, both during peace and wartime operations. Due to the advent of new technology, radio frequency line-of-sight (RF LOS) communications have come to the forefront of current operations, leaving the fleet vulnerable when conducting operations in an emissions controlled (EMCON) environment. In addition, the use of QR codes can circumvent the issues associated with Hazards of Electromagnetic Radiation to Ordinance (HERO) as well as provide a new effective method for conducting Identification Friend Foe/Neutral (IFFN). The ultimate goal of this thesis is to initiate new efforts that provide the fleet with an option for a new visual communication method. The need for a reliable visual line-of-sight (LOS) communications method has become apparent. This work proposes the tactical use of QR codes for visual communications, conveniently described as Digital Semaphore. QR codes have the ability to become the newest and most effective method of visual communication, replacing older, less effective forms. This thesis examines the use of various sensors and cameras to read and decode QR codes, and also proposes new practical uses of QR codes for communications on board ships, aircraft, and unmanned vehicles. Prototype software is provided as an initial-candidate QR Tactical Decision Aid (TDA). The ultimate goal of this thesis is to provide the fleet with an option for a visual communications method that allows ships and other units operating in a tactical emissions controlled environment to minimize communications vulnerability and maximize operational effectiveness. http://archive.org/details/digitalsemaphore1094534727 Outstanding Thesis Lieutenant, United States Navy Approved for public release; distribution is unlimited.