WASHINGTON — A nuclear engineer for the U.S. Navy and his wife have been charged with trying to share some of the United States’ most closely held secrets on submarine technology with another country, according to court documents unsealed on Sunday.
The engineer, Jonathan Toebbe, was accused of trying to sell information on the nuclear propulsion system of Virginia-class attack submarines — the technology at the heart of a recent deal that the United States and Britain struck with Australia.
While rivals like Russia and China have long sought details of U.S. submarine propulsion, based on the details in the court documents, some experts thought the unsolicited offer could have been aimed at a friendly country, not an adversary.
There is no allegation from the F.B.I. or the Justice Department that the foreign country obtained any classified information. But Mr. Toebbe had high-level clearances in nuclear engineering, and his service record showed that as a member of the Navy Reserve, he worked for 15 months from the office of the chief of naval operations, the top officer in the Navy.
The F.B.I. affidavit described the Toebbes as employing somewhat sophisticated encryption methods but extremely sloppy practices as they communicated with who they thought were representatives of a foreign power but turned out to be FBI agents. They insisted on careful use of cryptocurrency and encrypted their messages, but they were lured into depositing the information, usually on small digital cards, at sites where they could be easily observed.
Mr. Toebbe has worked for the military as a civilian since 2017. He was commissioned in the Navy and rose to the rank of lieutenant before moving to the Navy Reserve, which he left in December 2020 — the month the F.B.I. began contacting him.
According to court documents, he has worked on naval nuclear propulsion since 2012, including on technology devised to reduce the noise and vibration of submarines, factors that can give away their location. There is not much more detail in public Navy records. He worked on naval reactors in Arlington, Va., from 2012 to 2014. He then was a student at naval reactor school in Pittsburgh before returning to Arlington to work on reactors again.
The classified material in question included designs that could be useful to many countries building submarines. In the Australia deal, the United States and Britain would help the country to deploy nuclear-powered submarines, which are equipped with nuclear propulsion systems that offer limitless range and, under some circumstances, can run very quietly so that they are hard to detect.
Nuclear propulsion is among the most closely held information by the U.S. Navy, in part because the reactors are fueled by highly enriched uranium, which can also be converted to bomb fuel for nuclear weapons. Building compact, safe naval reactors is also a difficult engineering task. Until the deal with Australia, the United States had shared the technology with only Britain, starting in 1958.
According to the court documents, the investigation into the Toebbes began in December, when the F.B.I. obtained a package that had been sent to another country with operational manuals, technical details and an offer to establish a covert relationship. The package was intercepted in the other country’s mail system and sent to an F.B.I. legal attaché. The agency has such attachés in 63 countries.
“Please forward this letter to your military intelligence agency,” a note in the package read. “I believe this information will be of great value to your nation. This is not a hoax.”
The package was received by the foreign country in April 2020, although the F.B.I. did not gain access to it until December. The reason for the delay was unclear. The documents do not say whether the country that received the package gave it to the F.B.I. or the bureau obtained it through a secret source.
The F.B.I. followed the instructions in the package and began an encrypted conversation, in which the sender offered Navy secrets in return for $100,000 in cryptocurrency.
Over a series of exchanges, the F.B.I. persuaded the sender to leave information at a dead drop in return for cryptocurrency payments. The F.B.I. then observed Mr. Toebbe and his wife, Diana Toebbe, at the location of the drop, in West Virginia.
With Ms. Toebbe acting as a lookout, Mr. Toebbe left an SD card concealed inside half a peanut butter sandwich in a plastic bag, according to the court documents. After the undercover agent retrieved the sandwich, Mr. Toebbe was sent $20,000.
Agents then set up another dead drop in Pennsylvania and a third in Virginia, where they said Mr. Toebbe deposited an SD card concealed in a package of chewing gum.
While working at the Bettis Atomic Power Laboratory, a little-known government research facility in West Mifflin, Pa., Mr. Toebbe would have had access to the documents that he is accused of passing to the undercover F.B.I. officer.
Many of the details of the exchanges were redacted in the court documents, but there was a reference to scaled drawings and maintenance details. The F.B.I. cited a note, which the affidavit suggests was written by one of the Toebbes, saying that the information “reflects decades of U.S. Navy ‘lessons learned’ that will help keep your sailors safe.”
Submarine secrets have been the stuff of spy games for generations. Although the Cold War is long over, the technology, if anything, is more important than ever, especially as the United States steps up patrols in the Pacific.
The ubiquitousness of imagery satellites and the proliferation of ship-killing missiles have led countries to put a premium on vessels that can travel undetected and strike suddenly. That was a key factor in admitting Australia into the small club of nations that can deploy nuclear-powered submarines.
Diesel-powered submarines can stay underwater for only a few weeks at most before they must surface for refueling; their nuclear-powered equivalents can remain submerged for months. Australia initially agreed in 2016 to buy a fleet of diesel submarines from France, but with the project running behind schedule and over budget, it was lured away by the offer from the United States and Britain to join them in replicating their nuclear-powered subs. It will be years, however, before those are deployed, Biden administration officials say.
The F.B.I. and the Naval Criminal Investigative Service arrested Jonathan and Diana Toebbe on Saturday. They will appear in federal court in Martinsburg, W.Va., on Tuesday.
The Toebbes live in a middle-class neighborhood in Annapolis, Md. Neighbors said about a dozen black S.U.V.s descended on their street shortly after 1:15 p.m. on Saturday. Agents poured out and knocked on the door of the Toebbes’ split-level house. Eventually some 30 agents were present.
Several of them spent hours searching the Toebbes’ Mini Cooper, removing its seats and other components. Agents also interrupted a neighbor who was hosting a birthday party across the street to ask about the couple.
Neighbors said the agents remained in the house until about 9 or 10 p.m., apparently taking photographs; flashes could be seen through the windows.
Few neighbors wanted to speak on the record about the family, but several said the Toebbes were standoffish, more likely to ignore waves than to return them.
Jerry LaFleur, who shares a backyard fence with the couple, said he had occasionally waved to Mr. Toebbe, but the only time they spoke was when Mr. LaFleur asked permission to trim the weeds on Mr. Toebbe’s side of the fence.
“He seemed like a nice, ordinary guy, nothing that would make me think twice,” Mr. LaFleur said.
According to neighbors, the Toebbes have two children, who briefly returned to their home on Sunday to collect items. Ms. Toebbe is a humanities teacher at the Key School, a private school in the neighborhood known for a progressive philosophy. The school said on Sunday that she had been suspended indefinitely.
Julian E. Barnes reported from Washington, David E. Sanger from Vermont and Brenda Wintrode from Annapolis, Md. Adam Goldman and Eric Schmitt contributed reporting from Washington.