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 primarily 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 <WSD>extent</WSD> 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:  the distance or area or volume over which something extends