WASHINGTON — Minutes before U.S. fighter jets took off to begin strikes against Iranian-backed Houthi rebels in Yemen last month, Army Gen. Michael Erik Kurilla, who leads U.S. Central Command, used a secure U.S. government system to send detailed information about the operation to Defense Secretary Pete Hegseth. The material Kurilla sent included details about when U.S. fighters would take off and when they would hit their targets — details that could, if they fell into the wrong hands, put the pilots of those fighters in grave danger. But he was doing exactly what he was supposed to: providing Hegseth,...