I work in the medical field in the US armed forces. The military had been cataloging DNA of its members for some time now. The reason most people think of when condisering the why of this is that its for identification of remain. This is part true. DNA sampling is done for two reasons. The first is for identification of remain. The second reason is a little more insidious.
reason #2 - The Govt screens the DNA for rare disease markers. Once something is found, just a marker for potiential mind you, the member is usually given an option due to a "potiential" for future medical costs/disability. Sort of a form of genetic discrimination.