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, including in contested areas of the South China Sea and off the coast of North Korea.
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.