WASHINGTON—The Defense Department’s inspector general is investigating a major security breach after Chinese hackers allegedly stole large amounts of sensitive data from a Navy contractor, according to military officials.
The Chinese hackers allegedly stole data pertaining to submarine warfare that included secret plans to build a supersonic antiship missile the U.S. military planned to install on American subs, according to officials. The hackers targeted an unidentified company under contract with the Navy’s Naval Undersea...