During Vessey's tenure, there was increased emphasis on space as a theater of operations. In early 1983, the Joint Chiefs mentioned to the President that defense against nuclear-armed missiles might be technically feasible in the next century. To their surprise, Reagan seized upon the concept and on March 23, 1983, announced his vision of the Strategic Defense Initiative (SDI). Realizing the enormous military advantages to be gained from operations in space and to support SDI, the JCS recommended the establishment of a unified command for space. US Space Command was activated on September 23, 1985.