By the Vietnam era, the Army began planning for a more modern hospital and opened a new ten-story, 550-bed facility in 1969. The new Letterman Army Medical Center trained a quarter of the Army's medical specialists and served soldiers wounded in Vietnam throughout the 1970’s. In 1971, the adjoining Letterman Army Institute of Research opened to promote development of artificial blood, laser physics, and the treatment of trauma. During these years, the Army began demolishing parts of the 1899 quadrangle to build housing for nurses and enlisted men; the remaining historic buildings housed support services. By the late 1980’s, Letterman served mainly military retirees and their dependents. Following the transfer of the Presidio to the National Park Service, both the hospital and the research institute were deactivated in 1995.