The on-call national language capacity refers to the national ability in dealing with emergent demand of language skills related to the national strategic interest both at home and overseas. Drawing upon the extensive data online available and the limited academic literature, this paper reviews the development and experiences of the U.S. National Language Service Corps (NLSC). Based on national security needs, the key content of US national security language policy is to build on-call national language capacity to providelanguage emergency service. I endeavor to describe the background of the on-call national language capacity development in terms ofvolunteer service, following by a discussion about its framework, operational mechanism, features and achievements. In view of the status and problems of China’s developing“language volunteer service”, the paper also offers insights from the practice of NLSC andputs forward some suggestions on enhancing the on-call language capacity of China.