The US Navy has censured three rear admirals over a widening bribery scandal centred on a Singapore-based contractor who admitted to showering officers with cash, gifts and prostitutes to further his firm's interests.

Secretary of the Navy Ray Mabus issued letters of censure to Terry Kraft, Michael Miller and David Pimpo over their roles in the Glenn Defense Marine Asia (GDMA) corruption case, he said in a statement.

"These three officers, whose actions were revealed during the GDMA investigation, demonstrated poor judgment and a failure of leadership in prior tours," Mabus said.

The Navy added that the letters "ensure that individuals are held appropriately accountable when less than criminal allegations are substantiated."

The three admirals had improperly accepted gifts; two were found to have improperly endorsed a commercial business; and one solicited gifts and services while deployed aboard the nuclear-powered aircraft carrier USS Ronald Reagan between 2006 and 2007, the letters said.

All three men have sought retirement, requests Mabus said would be processed.

None of them could be immediately reached through the Navy for comment.

The company held more than $200 million in contracts for ship husbandry and maintenance for the Seventh Fleet in several Asian Pacific ports, including those in Singapore, Thailand, Japan and Malaysia.

On Jan. 15, its chief executive, Leonard Glenn Francis, pleaded guilty to federal conspiracy charges.

Since October, four Navy officers and two more company officials have also pleaded guilty to conspiracy to commit bribery. Two other Navy officers have pleaded innocent to bribery charges.

Last Tuesday, a former Navy contracting official became the ninth person charged in the case.