On March 1, 1997, the National Security Industrial Association (NSIA) merged with the American Defense Preparedness Association (ADPA), and the merged organization was renamed National Defense Industrial Association to reflect the equal contributions of both associations to the merger and to preserve the identity and reputation of each. The merger of these two preeminent associations concerned with the defense of the United States reflects the continuing demand for greater efficiency within the defense industry and the government defense agencies.

American Defense Preparedness Association

Founded in 1919 as the Army Ordnance Association, the American Defense Preparedness Association (ADPA) was a national organization dedicated to fostering progress in science, engineering, education, and management for the national defense. It was a nonpolitical and nonprofit-making organization dedicated to preparedness for the common defense and national security. Its principal missions were to increase weapons technology, improve defense management, and maintain a strong science-industry-defense team continually responsive to all needs of the development, production, logistics, and management phase of national preparedness.

In 1948, its name was changed to American Ordnance Association to reflect the changes brought about by the establishment of the Department of Defense. At that time, the Association broadened its technical coverage and activities to include material and interests of all Services.

On January 1, 1965, the Armed Forces Chemical Association and the American Ordnance Association merged and continued as the American Ordnance Association. The Association continued to broaden its technical competence to encompass the changing complex technology and management needs of the modern military forces.

To reflect its expanded interests and capabilities more adequately the name of the Association was changed to American Defense Preparedness Association on July 1, 1973.