She said it would be “inappropriate to discuss further details at this time.”

China and the United States have been locked in an escalating fight over cyber and military technology, with Beijing making rapid gains in recent years. American officials — from both the Trump administration and the Obama administration before it — concede that Washington has struggled to deter Chinese hacking, and have predicted the cyberattacks will increase until the United States finds a way to curb them.

The theft of the Navy system is hardly the largest, or the most sensitive, of the designs and systems stolen by Chinese hackers over the years. But it underscores a lesson the American government keeps learning: No matter how fast the government moves to shore up it cyberdefenses, and those of the defense industrial base, the cyberattackers move faster.

The plans for the F-35, the nation’s most expensive fighter jet in history, were taken more than a decade ago, and the Chinese model looks like an almost exact replica of its American inspiration.

A People’s Liberation Army unit, known as Unit 61398, was filled with skilled hackers who purloined corporate trade secrets to benefit Chinese state-owned industry. But many of its targets were defense related as well. Members of the unit were indicted in the last two years of the Obama administration, but none are likely to come back to the United States to stand trial.

The most sophisticated hack of American data took place at the Office of Personnel Management. It lost the files of about 21.5 million Americans who had filed extensive questionnaires for their security clearances. The forms listed far more than Social Security numbers and birth dates. They detailed medical and financial histories; past relationships; and details about children, parents and friends, particularly non-United States citizens.