A US Navy nuclear engineer and his wife were sentenced to long prison terms on Wednesday for plotting to sell submarine secrets to a foreign country.

Jonathan Toebbe, 44, and his wife, Diana Toebbe, 46, pleaded guilty in February to conspiring to sell information about the Navy’s nuclear propulsion systems.

Jonathan Toebbe was sentenced to 19 years and three months in prison, while his wife Diana Toebbe, 46, received a sentence of 21 years and eight months, the Justice Department said.

According to court documents, Diana Toebbe acted as a lookout while her husband provided top-secret information about nuclear-powered submarine technology to the unidentified foreign buyer in a series of clandestine “dead drops” in the area around their home in Annapolis, Maryland.

As a teacher at a private school, she initially pleaded not guilty to charges of conspiracy to transmit restricted data.

But she changed her plea after her husband pleaded guilty while admitting his wife was involved in the conspiracy.

Jonathan Toebbe was a nuclear engineer for the US Navy working on nuclear submarine propulsion systems when the two were arrested on October 9, 2021 after revealing a small SD card containing US secrets at a West Virginia airdrop site had hidden.

Court documents described an enticing, spy-novel-esque conspiracy in which they traveled hundreds of miles to covertly pass information, accept cryptocurrency payments and follow signals emanating from an embassy building in Washington.

In a statement, Toebbe stated that he had been considering his approach for several years and was happy to be working with “a reliable professional partner”.

He also wrote that he divided all the data collected into 51 “packages of information” and charged $100,000 for each.

But the FBI pursued the conspiracy after being alerted by the target country in December 2020, although that was almost nine months after the Toebbes first sent their offer to the country’s military intelligence agency.

The country that cooperated with the FBI investigation has not been identified.

One of the Toebbes’ communications suggested that English may not be the country’s native language, 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 plans to buy one or more from the United States.