Joseph Daniel Schmidt, 29, who served in an army intelligence unit from 2015 until 2020, is charged with retaining national defense information and attempting to deliver it to China.

The Justice Department said Schmidt, after leaving the military, offered national defense information to the Chinese consulate in Turkey and the Chinese security services.

In March 2020, Schmidt, who had access to secret and top secret information while serving in the 109th Military Intelligence Battalion at Joint Base Lewis-McChord in Washington state, went to Hong Kong, where he "continued his efforts to provide Chinese intelligence with classified information."

"He allegedly retained a device that allows for access to secure military computer networks and offered the device to Chinese authorities to assist them in efforts to gain access to such networks," the department said.

Schmidt stayed in China, primarily in Hong Kong, until his return to the United States on Friday. He was arrested upon arrival in San Francisco.

"Members of our military take a sworn oath to defend our country and the Constitution," acting US attorney Tessa Gorman said.

"In that context the alleged actions of this former military member are shocking -- not only attempting to provide national defense information, but also information that would assist a foreign adversary to gain access to Department of Defense secure computer networks."

Schmidt could face up to 20 years in prison.

His arrest comes two months after two members of the US Navy were arrested on suspicion of spying for China.

Jinchao Wei, who served on the amphibious assault ship the USS Essex in San Diego, allegedly handed over dozens of documents, photos and videos detailing the operation of ships and their systems.

Petty Officer Wenheng Zhao, who served at a naval base near Los Angeles, allegedly spied for China for nearly two years.