Truman era SecDef Robert A. Lovett, a Naval aviator who flew with the Marines and the British Naval Air Service, and eventually commanded a U.S. Navy aviation squadron as a Lt Commander comes to mind. Granted, Marines and pre-WWII Naval Air ops aren't quite SpecOps, but were the cutting edge of the armed forces of their day as much as the snakeeaters and sugarcookies today are now. Then, they were the mavericks and miracle workers, now, they're a part of the establishment they once battled.
His real contribution was in arranging the massive buildup od aircraft for WWII though, building up the aviation forces of all services not only with enough aircraft but the right type. At the level of a SecDef, a background in administrative logistics probably really is more of a useful trait than a history of triggerpulling and mudfoot operations. But an understanding of those who do so, if not the specific methodology itself, remails essential.
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