"defense purpose" is a correct and usable phrase in written English.
You can use it whenever you need to refer to something which serves the purpose of protection or security, such as in the sentence: "The military research team was focused on developing a new technology for defense purposes."
He laid the foundations for the indigenous development of nuclear technology for defense purposes.
KMOX was one of a handful of "clear" radio channels set aside years ago for national defense purposes.
He could not say, however, whether China was also using the computer for defense purposes such as nuclear weapons research.
In the era of the cold war military, for example, research for defense purposes developed the use of satellites for communication and created the Internet.
Moreover, it was explicitly based on "the President's determination that after the 11 September 2001 terrorist attacks in the United States, an extraordinary emergency existed for national defense purposes".
He was a marked individualist and served the shogun by applying his talents to topographical drawings used for national defense purposes.
Mr. Inouye, who lost his right arm in combat during World War II, also persuaded the United States military to leave its bases in Hawaii open, even though the state is no longer as vital for strategic defense purposes.
The dorsal fin is usually divided into two parts, with the first part supported by one or more spiny rays; these rays are believed to have evolved for defense purposes.
Why was this site selected for the depot? A. This site, having been previously recognized for its purpose during World War II as a supply depot and Army Quartermaster depot, received war assets and strategic materials, which were relocated here and stockpiled over time for national defense purposes.
The document does say that the actions of the American-led force in rebuilding Iraq "are indispensable for national security and national defense purposes," and that allowing only members of the allied force to bid for the contracts was intended both as a reward and an incentive for further cooperation in the future.
