Things got ugly for Cpl. Tyson Manker in Iraq. During a firefight in the confusion of the 2003 invasion, the 21-year-old Marine shot up a bus full of civilians. Later, during a chase, he dropped an Iraqi in a flowing white robe with a shot to the torso, only to discover afterward that he had hit a teenage girl. His squad beat detainees and accidentally shot several other civilians.After his deployment, Manker was kicked out of the Marine Corps with an other-than-honorable discharge ó not for anything that happened in combat, but for smoking marijuana to try to quiet his nerves when he got home.The military has increasingly acknowledged in recent years that there are tens of thousands of Mankers ó troops whose brutal experiences left them with post-traumatic stress disorder and who were then pushed out of the military for misconduct. Many were given other-than-honorable discharges that stripped them of veteransí benefits.The Army and the Air Force have moved in recent years to make it easier for these veterans to get their discharges upgraded to honorable. But not the Marine Corps.The office that oversees discharges for the Navy and Marines, the Naval Discharge Review Board, rejects nearly 85 percent of requests for upgrades relating to PTSD, compared with 45 percent for the Army board.Manker, now 36, applied for an upgrade in 2016 and was turned down. "It seems like the board doesnít even look at the issues," he said in an interview. "They just say no."A group from the Yale Law School filed a federal class-action lawsuit Friday against the Navy on behalf of Manker and other Navy and Marine veterans, arguing that behind their denials was "a systemic institutional bias or secret policy that discriminates against applicants who suffer from PTSD."The case, filed in New Haven, Conn., is the latest in a series of lawsuits by the universityís Veterans Legal Services Clinic seeking recognition that vast numbers of veterans, dating back to the Vietnam era, have been improperly discharged and denied the benefits that were meant to help them re-enter society.A main focus has been the boards for corrections of military records in each branch of the military. These boards have the power to restore a veteranís eligibility for health care and education benefits by upgrading their discharges to honorable.The boards were created after World War II, when Congress recognized that disciplinary decisions made quickly under wartime pressure by military commanders often contained mistakes and that in the aftermath, veterans deserved an avenue for due process to correct them, according to Jonathan Petkun, one of the Yale students who filed the lawsuit."We donít see that happening now," said Petkun, a former Marine captain who served in Iraq and Afghanistan. "The board seems to just be rubber stamping things.""As a former officer, I think commanders in the field need broad discretion," he said. "But when I was an officer, I thought, if I made a mistake, veterans would have recourse. Now I see that is rarely the case."Yale students working with veterans groups have gradually forced the Pentagon to be more open to correcting what veterans groups largely view as unfair discharges. In 2014, in response to a lawsuit by Yale and the group Vietnam Veterans of America, Defense Secretary Chuck Hagel issued new guidelines for upgrading discharges. The guidelines instructed the review boards to give "liberal consideration" to the possibility that PTSD contributed to a veteranís other-than-honorable discharge.The Army board quickly changed course, and its denial rate for applications involving PTSD fell from 96 percent to about 45 percent, according to Department of Defense data. The Air Force made similar changes. But the Navy board, which oversees both sailors and Marines, has scarcely budged.Brad Carson, who oversaw the Army board as an undersecretary in the Obama administration, said the boards were overworked and had only a few minutes to review each case. But even with more time, he said, it is far from simple to reach a fair outcome in cases where a veteran clearly committed misconduct and also has a stress-disorder diagnosis."How do you determine how PTSD affected an action, which might also be due just to, well, being a bad soldier?" he said in an interview. "The Navy has a strong cultural belief, going back centuries, that you do not second-guess commanders. I suspect because of that, when they have a difficult case, they fall back on tradition and defer to commanders."A Navy spokesman said that its boardís staff was too busy to comment for this article.