An 83-year-old Catholic nun and two of her fellow peace activists were found guilty Wednesday of intending to harm national security when they intruded in July onto the Y-12 National Security Complex, a nuclear-weapons production facility in Oak Ridge, Tenn.

After hearing two days of testimony and arguments, and then deliberating for nearly 21 / 2 hours, the jury of nine men and three women also found the defendants guilty of damaging more than $1,000 in government property at the Y-12 site — where they cut through four chain-link fences and spray-painted biblical messages of nonviolence on a building that warehouses an estimated 400 tons of highly enriched uranium, the radioactive material used to fuel nuclear weaponry.

During the trial, dozens of spectators filled two courtrooms to support Sister Megan Rice and 64-year-old Vietnam War veteran Michael Walli, both of whom live in the District, and Greg Boertje-Obed, a 57-year-old house painter who lives in Duluth, Minn. In the predawn hours of July 28 last year, the three activists hiked over a wooded ridge and were able to enter the site unimpeded because of a series of deficient security measures, including inoperable surveillance cameras and a monitoring system that was compromised by routine false alarms.

As the jury left the courtroom at U.S. District Court in downtown Knoxville just after 6 p.m., supporters sang softly toward the activists: “Love, love, love, love. People, we are made for love.” Rice, smiling and wearing a T-shirt imprinted with “I wish to live without war,” turned up her palms and bowed to supporters.

Judge Amul Thapar ordered the trio into custody but scheduled a hearing for Thursday on the merits of their detention. After the verdict, the judge and lawyers could not agree on whether harming the national defense — which falls under the “sabotage” chapter of the U.S. code — is a “crime of violence” and therefore requires immediate remanding. The activists have been free and compliant with the terms of their release since their initial arrest and incarceration.

“Pretty obscene but not terribly surprising,” said Baltimore resident Ellen Barfield, a supporter of the activists who spoke about the verdict to the news media outside the courthouse. “Did they have to slam them into jail?”

In its closing arguments, the defense contended that the activists intruded into Y-12 as a symbolic act in support of the peaceful transformation of nuclear-weapons programs to nonviolent initiatives. Assistant U.S. Attorney Jeffrey Theodore argued that the activists’ intent was to target and disrupt operations at Y-12 — which closed for two weeks after the break-in to beef up security — and that such a disruption hindered national-defense preparedness and the credibility of the U.S. nuclear deterrent.

“Y-12 makes nuclear weapons for the national defense,” Theodore told the jury. “When you interfere with Y-12, you interfere with the national defense of the United States. . . . Do you excuse what a burglar did because the homeowner was a little lax with security?”

“Three senior citizens showing up with backpacks is a threat to the United States of America?” defense attorney William Quigley asked rhetorically. “That threatens us? I don’t think so. . . . Opposing [nuclear weapons] is not something that opposes the national defense of the United States.”

Earlier Wednesday on Capitol Hill, at a Senate subcommittee hearing on strategic forces programs, the acting administrator of the National Nuclear Security Administration called the Y-12 intrusion “completely unacceptable” and an “important wake-up call.” The security administration is a semiautonomous agency within the Energy Department that is tasked with securing and managing the country’s nuclear weapons and material.

“The severity of the failure of leadership at Y-12 has demanded swift, strong and decisive action by the department,” said acting administrator Neile Miller, according to the Associated Press. “Since the Y-12 incursion, major actions have taken place to improve security immediately, and for the long term.”

Sentencing for Rice, Walli and Boertje-Obed is expected within four months. Together, the two felonies carry a maximum sentence of 30 years in prison. Defense attorneys have filed a motion for acquittal on the “sabotage” charge because they think the government did not provide sufficient evidence to sustain a conviction.

As the defendants were led out of the courtroom and into custody, supporters called out, “Thank you, Michael!” and “Thank you, Greg!” and “Thank you, Megan!”