A former US Navy captain has pleaded guilty to criminal conflict of interest charges after it emerged that he had provided secret public relations services for a defense contractor at the heart of the so-called "Fat Leonard" bribery scandal.

Jeff Breslau is one of dozens accused or convicted in the Pacific-wide corruption scandal, the biggest in US Navy history.

According to the US Department of Justice, the former officer, who retired with the rank of captain, received $65,000 from Leonard Francis -- the contractor who pleaded guilty in 2015 to bribery and fraud charges.

Breslau provided "consultation services" to Francis' Singapore-based company, including ghostwriting emails to Navy personnel from Francis, providing talking points to to the defense contractor in advance of his meetings with Navy officials, and providing other advice.

He did not disclose the role, nor the payments, to Navy command.

From 2009 until 2012, Breslau was assigned as director of public affairs for the US Pacific Fleet, according to a Justice Department press release.

It was from the tail end of his time in the role, and into his next posting at the Joint Public Affairs Support Element in Norfolk, Virginia, that he provided Francis with consulting services.

From March 2012 to September of the following year he "authored, reviewed or edited" dozens of documents, as well as writing at least 135 emails providing advice to Francis, and least 14 instances of providing talking points in advance of meetings that the contractor held with high-ranking Navy personnel.

In addition he "'ghostwrote' numerous emails on Francis' behalf to be transmitted to US Navy personnel," according to prosecutors.

According to Breslau's plea agreement, his "willful illegal conduct" in providing consulting services to Francis and his Singapore-based ship husbanding company Glenn Defense Marine Asia (GDMA) "substantially disrupted the functions of the US Navy."

Breslau, who is scheduled to be sentenced in February, faces up to five years in prison and up to a $250,000 fine for his role in the scandal.

Biggest Navy scandal in history

The investigation into what would emerge as the largest corruption scandal in US Navy history began in 2013, and has touched on capitals and ports across the Pacific, including Singapore, Tokyo, Bangkok and Manila.

In March 2017, acting US Attorney Alana Robinson described it as "fleecing and betrayal of the United States Navy in epic proportions, (which) was allegedly carried out by the Navy's highest-ranking officers."

Since the investigation began, multiple Navy officials have been arrested and accused of accepting cash, prostitutes and all-expenses-paid trips in exchange for steering ships to ports where Francis' company operated, providing services such as fuel and tugboats.

In June of last year, Michael Brooks, who served as the US naval attaché at the US Embassy in the Philippines from 2006 to 2008, was sentenced to 3.5 years in prison after admitting to using his influence to benefit Francis in exchange for "bribes of travel and entertainment expenses, hotel rooms and the services of prostitutes," the Justice Department said.

Along with prostitutes, Francis and his company provided scores of US Navy officers with tens of millions of dollars in bribes, including cash, luxury travel, Cuban cigars, Kobe beef and Spanish suckling pigs, prosecutors said.

Francis, whose nickname comes from his then 400-pound heft, admitted bribery and fraud charges in 2015.