Four people have been arrested in the United States for allegedly passing secret defence information to China.
Details about the space shuttle may have been passed on to China
A 72-year-old former Boeing engineer is accused of giving China details about the space shuttle and other aerospace programmes.
In a separate case, two men and a woman are accused of handing over US defence department documents about Taiwan.
A US justice department spokesman said the cases represented serious breaches of national security.
Chinese-born Dongfan "Greg" Chung, 72, of California, faces charges including eight counts of economic espionage, conspiracy, and making false statements to FBI investigators.
The US justice department said Mr Chung, a naturalised US citizen, worked in the aerospace industry for about 30 years - mostly at Rockwell International and Boeing on the space shuttle programme.
It added that he retired in 2002 but was working for Boeing as a contractor until 2006.
The charges claim he took Boeing trade secrets relating to the space shuttle, the C-17 military transport aircraft and the Delta IV rocket for the benefit of China.
He is also said to have sent China 24 secret manuals relating to the B-1 Bomber.
Mr Chung received instructions from Chinese officials from as early as 1979, prosecutors said.
In a letter he sent back to China, he is reported to have expressed "a desire to contribute to the Motherland", US Attorney Tom O'Brien told reporters.
Mr Chung is thought to have had links to Chinese-born engineer Chi Mak, who was found guilty of conspiring to export sensitive defence technology from the US to China last year, the justice department said.
If convicted, Mr Chung faces about 100 years in prison.
In a separate case, a defence department employee and two others are accused of passing US government documents and information to China. The three suspects are Tai Shen Kuo, 58; Yu Xin Kang, 33; and Gregg William Bergersen, 51.
Mr Bergersen, a weapons systems policy analyst for an agency within the defence department, was charged with conspiracy to disclose national defence information "to persons not entitled to receive it".
Tai Shen Kuo and Yu Xin Kang are charged "with conspiracy to disclose national defence information to a foreign government".
Mr Kuo has Taiwanese and US passports and is alleged to have cultivated a relationship with Mr Bergersen to get information including details of potential sales of US military goods to Taiwan, according to court documents.
Ms Kang, a Chinese national living in the US, ferried information between Mr Kuo and Chinese officials, prosecutors said.
Mr Kuo and Ms Kang each face up to life in prison if convicted. Mr Bergersen faces up to 10 years in prison.
Assistant Attorney General for National Security Kenneth Wainstein said the cases represented different styles of espionage, but both with the same objective.
"Certain foreign governments are committed to obtaining the American trade secrets that can advance the development of their military capabilities," he said.
"Today's case demonstrates that the justice department is equally committed to foiling those efforts through the arrest and prosecution of those who conduct economic espionage at the expense of our economic and national security."