A Navy officer has spent eight months in the brig as a captive of U.S. counterintelligence agents, but to hear officials tell the spy tale, they know few details about what he provided to China’s communist regime or Taiwan’s government. To be sure, Lt. Cmdr. Edward Chieh-Liang Lin knows a lot about the Navy’s spying on China. He was a naval flight officer for long-distance patrol aircraft that suck up communications as well as track and take reconnaissance photographs and video of Beijing’s aggressive military operations in the South China Sea and elsewhere. “Someone like Cmdr. Lin would have detailed...