Rear Adm. Robert Gilbeau (U.S. Navy)

A one-star Navy admiral pleaded guilty Thursday to a felony charge of lying to federal investigators in the wide-ranging “Fat Leonard” corruption scandal, marking an exceptionally rare instance of a flag officer being criminally prosecuted for actions while in uniform.

In a plea deal with prosecutors, Rear Adm. Robert Gilbeau, a special assistant to the chief of the Navy Supply Corps, admitted to concealing the duration and extent of his relationship with Leonard Glenn Francis, a Singapore-based defense contractor who showered Navy brass with prostitutes, cash and epicurean meals over a decade until his arrest in 2013.

Court papers show Gilbeau destroyed papers and computer files after Francis was arrested in an international sting operation and repeatedly minimized his contacts with the contractor when confronted by federal agents.

In the modern history of the Navy, only a handful of admirals have faced criminal prosecution. Just one admiral has been court-martialed since the end of World War II. A few others have been charged with crimes by civilian authorities shortly after they retired from the service.

Gilbeau is scheduled to be sentenced on Aug. 26 and faces a maximum of five years in prison, though federal guidelines dictate that he is likely to receive little, if any, time behind bars.

Prostitutes, vacations and cash: The Navy officials ‘Fat Leonard’ took down

The admiral appeared in U.S. District Court in San Diego on Thursday dressed in civilian clothes. He was carrying a little white dog, named Bella, that was wearing a vest with “Navy” emblazoned on it. Navy officials familiar with the case say the dog is a therapy animal to help treat Gilbeau for post-traumatic stress disorder.

Gilbeau is a 1983 graduate of the Naval Academy in Annapolis. He was awarded a Bronze Star and a Purple Heart for his service in Iraq in 2007. He also deployed to Afghanistan in 2012 and 2013.

He is the highest-ranking officer to be charged so far for his ties to Francis, a larger-than-life figure known in maritime circles as “Fat Leonard.” Francis has admitted to bribing “scores” of Navy officials with millions of dollars in a case that has mushroomed into the worst corruption scandal in the Navy’s history.

A federal prosecutor said last year that 200 individuals were under investigation. Of those, about 30 are admirals, Navy officials have said.

Including Gilbeau, 14 people have been charged so far in federal court. In addition, a former Navy contracting official has been charged with corruption by Singapore authorities. Prosecutors have said more arrests are expected.

“Of those who wear our nation’s uniform in the service of our country, only a select few have been honored to hold the rank of admiral — and not a single one is above the law,” said Laura Duffy, the U.S. attorney for the Southern District of California, whose office is leading the investigation. “Admiral Gilbeau lied to federal agents investigating corruption and fraud and then tried to cover up his deception by destroying documents and files.”

Even so, court papers filed in the case reveal few details about the extent of the relationship between Gilbeau and Francis, or why federal agents spent four years investigating the admiral.

Gilbeau admitted to falsely telling investigators that he never received gifts from Francis, but the documents do not specify what he did take — other than meeting with Francis for meals a few times a year.

“In this unfortunate situation, he accepts responsibility for the decisions he made and for his conduct,” David Benowitz, an attorney for Gilbeau, said in an email to The Washington Post. He did not elaborate.

Court papers suggest that Gilbeau came to know Francis starting in 2003 at the outset of several deployments to Asia. He served as a supply officer on the USS Nimitz, an aircraft carrier, and later headed a crisis response team in Singapore that provided relief to victims of a tsunami in Southeast Asia in December 2004.

According to several individuals familiar with the case, Gilbeau was also under investigation for his relationships with other contractors when he served in Afghanistan.

Gilbeau departed Afghanistan shortly after Francis, 51, was arrested in an international sting operation in San Diego in September 2013.

Francis has since admitted to bribing Navy officials with cash, sex and gifts worth millions of dollars so he could win more defense contracts and fleece the Navy of at least $35 million in excessive charges.

His company, Glenn Defense Marine Asia, provided critical support for the Navy’s 7th Fleet for a quarter-century by resupplying and refueling submarines and ships during hundreds of port visits in the Eastern Hemisphere.

In a statement, Adm. John Richardson, chief of naval operations, said Gilbeau’s “behavior is inconsistent with our standards and the expectations the nation has for us as military professionals. It damages the trust that the nation places in us, and is an embarrassment to the Navy.”

He said the Navy is fully cooperating with the Justice Department. But in strongly worded comments, he also indicated that the Navy’s leaders needed to do more to police themselves.

“We must go further,” he added. “We must hold ourselves accountable to the highest standards of behavior, and work tirelessly to restore any damage that has been done to these crucial relationships.”

Ray Mabus, the secretary of the Navy, credited NCIS, the Defense Criminal Investigative Service and other federal agents for doing “impressive work to discover the corruption in these cases.” He said the Navy now has “some of the strongest counter-fraud efforts in the government.”

Most of the officers who are under scrutiny have not been publicly identified. But the Navy has acknowledged that two admirals — Vice Adm. Ted “Twig” Branch, the director of naval intelligence; and Rear Adm. Bruce Loveless, another intelligence officer — are under criminal investigation.

The Navy announced last year that it had censured three other admirals for ethics violations after an internal investigation determined that they had accepted gifts and luxurious meals from Francis without proper recompensation.