Diana Toebbe, 46, admitted taking part in her husband Jonathan Toebbe's plan to sell information on US nuclear submarines to an unidentified foreign buyer.

According to the charges, she acted as a lookout while her husband delivered highly classified information on nuclear submarine technology to the buyer in a series of surreptitious "dead drops" in the region around their Annapolis, Maryland home.

A teacher at a private school, she initially pleaded innocent to the charge of conspiracy to communicate restricted data.

But last week Jonathan Toebbe, 43, pleaded guilty to the same charge, and in doing so admitted his wife took part in the plot.

While the charge could bring up to life in prison, Diana Toebbe's plea agreement set the maximum at 36 months.

Her husband faces at least 12 and a half years in prison.

Jonathan Toebbe was a nuclear engineer for the US Navy dealing with nuclear submarine propulsion systems when the two were arrested on October 9, 2021 after he hid a small SD card carrying US secrets at a dead drop location in West Virginia.

Court documents described a tantalizing, spy-novel like plot in which they traveled hundreds of miles to secretly hand over information, took payments in cryptocurrencies, and followed signals made from an embassy building in Washington.

In one message to the "buyers" Toebbe indicated that he had been considering his actions for several years and was happy to work with "a reliable professional partner."

He also wrote that he had divided all the data he had collected into 51 "packages" of information, and sought $100,000 for each.

But the FBI was following the plot, after having been alerted to it by the target country in December 2020 -- though that was nearly nine months after the Toebbes first mailed their offer to the country's military intelligence.

The country, which cooperated in the FBI investigation, has not been identified.

One of the Toebbes' communications indicated that English might not be the country's native tongue, and others suggest that the country's navy is familiar with nuclear propulsion technology.

Russia, China, Britain, France and India operate nuclear-powered naval vessels, and Australia is planning to buy one or more from the United States.