The "Fat Leonard" corruption investigation has expanded to include more than 60 admirals and hundreds of other U.S. Navy officers under scrutiny for their contacts with a defense contractor in Asia who systematically bribed sailors with sex, liquor and other temptations, according to the Navy.

Most of the admirals are suspected of attending extravagant feasts at Asia's best restaurants paid for by Leonard Glenn Francis, a Singapore-based maritime tycoon who made an illicit fortune supplying Navy vessels in ports from Vladivostok, Russia, to Brisbane, Australia. Francis also was renowned for hosting alcohol-soaked, after-dinner parties, which often featured imported prostitutes and sometimes lasted for days, according to federal court records.

The 350-pound Francis, also known in Navy circles as "Leonard the Legend" for his wild-side lifestyle, spent decades cultivating relationships with officers, many of whom developed a blind spot to his fraudulent ways. Even while he and his firm were being targeted by Navy criminal investigators, he received VIP invitations to ceremonies in Annapolis and Pearl Harbor, where he hobnobbed with four-star admirals, according to photographs.

The Justice Department has filed criminal charges against 28 people, including two admirals, since Francis was arrested in an international sting operation four years ago. Those cases comprise the worst corruption scandal in Navy history, but they represent a fraction of a much larger list of Navy officials under investigation but whose names have been mostly kept secret.

In response to queries from The Post, the Navy recently confirmed that it has been reviewing the conduct of 440 other active-duty and retired personnel — including 60 current and former admirals — for possible violations of military law or federal ethics rules in their dealings with Francis and his company, Glenn Defense Marine Asia.

That is double the number of admirals whom Navy officials said were under investigation last year. (The Navy has about 210 admirals on active duty).

The caseload has grown as the Justice Department has given the Navy additional dossiers of individuals who did not meet the threshold for prosecution in civilian courts, but may have committed offenses under the military justice system, officials said.

The Navy's handling of the cases has been largely opaque to the public. The Navy has identified only 10 of the 440 individuals who have come under military investigation and has divulged few details about their ties to Francis, even in cases that have been closed.

The vast majority of those under scrutiny are officers, according to the Navy. Officials said Francis targeted only a few enlisted sailors with his bribes.

Navy officials said revealing additional names or more information about their involvement could violate their privacy rights and compromise ongoing cases.

"The release of such information ... would likely reveal sensitive details about the breadth and scope of the criminal investigation and pending cases," Cmdr. Mike Kafka, a Navy spokesman, said in a statement.

So far, the Navy has charged five people with crimes — none of them admirals — under military law, charging documents show.

In addition, the Navy said it has determined that 40 people committed misconduct by violating ethics rules or other regulations. Their cases have been handled administratively, meaning they did not involve criminal charges.

In many instances, the Navy was prevented from taking tougher action because the statute of limitations under military law — five years for most felonies — had expired. The oldest matter reviewed so far dated to 1992, while most occurred between 2004 and 2010, according to a Navy official.

The official said the Navy has concluded that about half of those under review — 230 people — were not guilty of misconduct. Some were found to have had little or no contact with Francis. Many others attended dinners or accepted gifts, but the Navy determined that there were extenuating circumstances that excused their actions, said the official, who was authorized to speak only under the condition of anonymity.

Francis, 53, is in jail in San Diego as he awaits sentencing in federal court. He pleaded guilty in 2015 to bribing "scores" of Navy officials and defrauding the service of more than $35 million. One of his attorneys, Ethan Posner, declined to comment for this article.

Francis's widespread overbilling of the Navy had been an open secret for years. In response to a flood of fraud complaints dating to 2006, the Naval Criminal Investigative Service (NCIS) opened more than two-dozen separate investigations into Glenn Defense, according to law-enforcement records.

Most of the cases went nowhere, NCIS files show. Starting in 2009, however, NCIS escalated its efforts by assigning more agents to investigate Francis. They later opened a full-blown corruption inquiry on suspicion that some Navy officials were feeding him military secrets and inside information about defense contracts.

Despite being under the microscope, Francis was still able to rub shoulders with many of the Navy's top leaders.

In September 2011, for example, he was invited to the Naval Academy in Annapolis to attend a change-of-command ceremony for the Navy's highest-ranking officer.

During his visit, Francis posed for grip-and-grin photos with Adm. Jonathan Greenert, the new chief of naval operations, and the man he was replacing, Adm. Gary Roughead.

Roughead and Greenert both had encountered Francis during prior assignments in Asia and the Pacific. A Navy spokesman would not say whether they are among the 60 admirals under investigation; the names of most officers on the list have not been made public.

Roughead, who retired soon after the 2011 ceremony, said in an email that he couldn't "recall particulars" about who was invited to the event. He declined further comment.

In an email, Greenert said he had not been contacted by investigators and did not know how Francis came to be invited to the ceremony. He said he, Roughead and their spouses spent hours in a receiving line and posed for several pictures.

Of the two admirals, Greenert's previous contacts with Francis were more extensive, according to several individuals familiar with their relationship.

Greenert met the defense contractor in the late 1990s while serving as chief of staff for the Navy's 7th Fleet, which covers most of Asia. Their interactions continued after Greenert was promoted to vice admiral and took command of the fleet in 2003.

While in command, Greenert attended at least three dinners with Francis, according to two former senior Navy officials.

In December 2005, Greenert mailed Francis a holiday greeting card featuring a sketch of the USS Blue Ridge, the 7th Fleet flagship, which the contractor had often visited as a distinguished guest.

"Leonard — See you soon I expect. Recognize the ship?" Greenert joked in a handwritten note wishing him "Good health & happiness in 2006." A copy of the card was obtained by The Post.

Three months later, Greenert signed a letter on official stationery thanking Francis for the "superb services" his company provided to the Blue Ridge during several port visits in southeast Asia. "Over the years, the reputation of Glenn Marine remains exceptional," the letter stated. "Keep up the great work."

Francis treasured such letters, cards and photographs, which he promoted as proof of his close ties with the Navy's senior leaders. Greenert posed for photographs with Francis on at least two other occasions: aboard the Blue Ridge in 2005 and at a ceremony in Hawaii in 2009, according to copies of the images.

In his email to The Post, Greenert said it was not unusual for commanders to send correspondence to contractors acknowledging their "responsive and flexible" service. He also said he sent hundreds of official Christmas cards during his time as the 7th Fleet commander. He did not respond to questions about dinners he attended with Francis or his other interactions with the contractor.

Greenert's relationship with Francis later became a sensitive issue for NCIS agents.

As the law-enforcement probes into Francis and his company heated up in 2013, NCIS officials deliberately kept Greenert, who by then was chief of naval operations, in the dark, according to two former senior Navy officials with direct knowledge of the case.

Even after Francis was arrested, NCIS officials excluded Greenert from briefings about the case, restricting their reports to a handful of Navy civilian leaders and Adm. Mark Ferguson, who was then the vice chief of naval operations, according to the former senior officials.

In addition to Roughead and Greenert, Francis secured photo-ops with several other high-ranking admirals during his visit to the Naval Academy in 2011.

He also spent time in Annapolis with Vice Adm. Michael Miller, then the academy superintendent, who arranged for a personal tour of his official residence, Buchanan House, according to photographs obtained by The Post.

In a statement, Miller confirmed the meeting but said he had "no knowledge" that Francis was under investigation at the time.

"Mr. Francis requested a tour of the Naval Academy. We would have supported that request as we do numerous visitors every year," Miller said. He acknowledged that investigators had asked him about Francis's visit, saying he was "completely forthcoming on this subject with the Navy."

Miller said he did not invite Francis to the change-of-command ceremony. Two other Navy officials said the invitation probably came from the protocol office for the chief of naval operations, but did not know who put his name on the guest list.

The Navy later rebuked Miller with a formal letter of censure for failing to adequately reimburse Francis for lavish dinners and other gifts he received from the contractor years earlier when he commanded an aircraft carrier strike group in Asia. Miller retired from the Navy in 2015.

Four months after visiting Annapolis, Francis was a VIP guest at another Navy change-of-command ceremony: at the headquarters of the U.S. Pacific Fleet in Pearl Harbor, Hawaii.

On that occasion, Francis posed for photographs with Adm. Cecil Haney, the new Pacific Fleet commander, and his predecessor, Adm. Patrick Walsh, according to copies of those images.

Two former Navy officials who were present told The Post they were shocked to see Francis at the ceremony because the Pacific Fleet had been engaged in a years-long effort to tighten contract loopholes and sloppy billing practices that had enabled Glenn Defense to overcharge the Navy for millions of dollars.

They said they were even more surprised to see Francis afterward at a smaller, private party at Nimitz House, the official quarters for the Pacific Fleet commander.

In a statement, Haney said he didn't invite Francis and didn't know who he was before the ceremony.

"Any photo I took with him was most likely during the receiving line where I took numerous photos with so many in attendance that day," Haney said. He indicated that he had spoken with investigators, saying: "I have been completely forthcoming of this subject with the Navy."

In an interview, Walsh recalled Francis' presence at Pearl Harbor that day but said he didn't know who invited him.

"Leonard Francis had a way of showing up at all kinds of ceremonies," said Walsh, who retired from the Navy in 2012.

Walsh said he was aware at the time that Francis was under scrutiny by the Pacific Fleet for his billing practices, but did not know that the contractor was also under criminal investigation by NCIS. He said investigators have not questioned him about his contacts with Francis.

Walsh said he first met Francis during a port visit in Malaysia in 2004 when he served as the commander of the USS John C. Stennis aircraft carrier strike group. He said Francis invited him to one of his famous dinners, but that he didn't attend.

"I had a different set of priorities," he said.