Sentence:  Research and development activities undertaken by the Secretary shall be coordinated or conducted jointly with the Department of Defense to the end that developments under this Act which are <WSD>primarily</WSD> of a civil nature will contribute to the defense of the Nation and that developments which are primarily of a military nature will , to the greatest practicable extent compatible with military and security requirements , be available to advance the purposes of this Act and to strengthen the civil economy of the Nation . 
Meaning of the word marked with <WSD> tags:  for the most part