The Navy has been concerned with protecting its signals against unauthorized use since the Civil War. More dramatic developments in cryptology came after the advent of radio communications in the Navy about the turn of the century. Beginning almost with the first wireless transmission from a Navy ship in 1899, Sailors and Marines have been assigned duties in communications security and intelligence. They conducted numerous experiments in this new field of warfare during World War I and dedicated themselves to drawing appropriate lessons from this experience in the years following.
The Code and Signal section of the Naval Communications Service undertook some cryptologic duties when the United States entered the war in 1917. In July 1922, it was assigned the familiar organizational title OP-20-G, which was retained until after World War II. Between 1924 and 1935, the Naval cryptology service developed operationally, culminating in the formation of the Naval Security Group effective 11 March 1935. That date marks the first appearance of the word "Group" in the title of the Naval cryptology organization and is observed as the birth of the Naval Security Group.
A handful of officers and small cadre of enlisted personnel trained themselves during the interwar period in the specific skills and knowledge of Naval signals exploitation and security. These pioneers formed the nucleus of the Communications Intelligence Organization during World War II. At the height of the war, nearly 10,000 naval specialists participated in the world-wide activities of the Naval Security Group. Their contributions played a role in all major campaigns of the war.
After 1945, the Navy was reduced in size and the consolidation of functions became necessary. The Navy Cryptologic organization was renamed Communications Supplementary Activities in 1945 and the trend toward centralized control continued. Increasingly complex technology and more sophisticated equipment added new responsibilities and accelerated the movement toward career specialties in signal exploitation and security. In 1948, officer designators and enlisted ratings were established for cryptologic personnel. A closer alliance with Army and Air Force
cryptologists was formalized in 1949 with the establishment of the Armed Forces Security Agency. The title "Naval Security Group" was adopted in late 1950 and has remained the official name.
Naval Security Group personnel proved themselves in combat operations during the Korean conflict from 1950 through 1953. In 1952, the National Security Agency was created from the Armed Forces Security Agency, strengthening the bonds among service cryptologic elements. Experienced cryptologists who were veterans of both World War II and the Korean conflict continued to serve in the Naval Security Group throughout the decade of the 1950's. In 1956, the Naval Security Group Headquarters Activity was established, retaining the name until 1961 when it was redesignated the Naval Security Group Headquarters under the Director, Naval Security Group who assumed the title at the same time.
The eruption of hostilities in Southeast Asia and growing involvement of the United States Navy provided major impetus to the expansion of Naval signals exploitation and security in the 1960's. On 1 July 1968, the Naval Security Group Command was established under a flag officer. In March 1971, a reorganization within the Office of the Chief of Naval Operations formed the Signals Exploitation and Security Division; marking the separation of Cryptology from Communications for the first time in 50 years.
Until 2005 when CNSG was disestablished, the Commander, Naval Security Group Command was assigned additional duty in the Office of the Chief of Naval Operations as the Deputy Director of Naval Intelligence. A 1610 Flag Officer still performs these duties but he does not carry the title CNSG. The Naval Security Group Command and Naval cryptologists serving world-wide existed for the sole purpose of supporting Naval and national operations which provide for and ensure the defense of the United States. Those personnel are now integrated into Naval Network Warfare Command, the National Security Agency, Navy Information Operations Commands, various other shore units and the operating forces of the United States Navy.