A Navy nuclear engineer with access to military secrets has been charged with trying to pass information about the design of American nuclear-powered submarines to someone he thought was a representative of a foreign government.

He was, however, talking to an undercover FBI agent, the Justice Department revealed.

In a criminal complaint detailing espionage-related charges against Jonathan Toebbe, the government said he had sold information for nearly a year to a contact he believed represented an undisclosed foreign power.

Toebbe, 42, was arrested in West Virginia on Saturday along with his wife, Diana, 45, after he had placed a removable memory card at a pre-arranged “dead drop”.

The FBI says the scheme began in April 2020 when Toebbe sent a package of Navy documents to a foreign government and said he was interested in selling operation manuals and other sensitive information to that country.

Authorities say he also provided instructions for how to conduct the furtive relationship in a letter that said: “I apologize for this poor translation into your language. Please forward this letter to your military intelligence agency. I believe this information will be of great value to your nation. This is not a hoax.”

The FBI launched an undercover operation in which an agent posing as a representative of a foreign contact made contact with Toebbe and agreed to pay thousands of dollars in cryptocurrency for the information he was offering.

After weeks of back and forth over email, the undercover agent sent Toebbe about $10,000 in cryptocurrency, describing it as a sign of good faith and trust.

Weeks later, federal agents watched as the Toebbes arrived at an agreed-upon location in West Virginia for the exchange, with Diana Toebbe appearing to serve as a lookout for her husband during a dead-drop operation for which the FBI paid $20,000.

The FBI recovered a blue memory card wrapped in plastic and placed between two slices of bread on a half of a peanut butter sandwich, court documents say. The records on the memory card included design elements and performance characteristics of Virginia-class submarine reactors.

The Justice Department describes those submarines as “cruise missile fast-attack submarines, which incorporate the latest in stealth, intelligence gathering, and weapons systems technology.

“The memory card also included a typed message that said, in part: “I hope your experts are very happy with the sample provided and I understand the importance of a small exchange to grow our trust.”

The FBI conducted similar dead-drop exchanges over the next several months, including one in August in eastern Virginia for which Toebbe was paid roughly $70,000. In that instance, prosecutors say, he concealed in a chewing gum package a memory card that contained schematic designs for the Virginia-class submarine.

Toebbe has worked for the U.S. government since 2012, holding a top-secret security clearance and specialising in naval nuclear propulsion, the FBI says. He has also been assigned to a government-owned laboratory in the Pittsburgh area that officials say works on nuclear power for the U.S. Navy.

The Toebbes are expected to make their initial court appearances on Tuesday in Martinsburg, West Virginia.