Gray-haired Patrick Barnes still wears a crew cut and sits ramrod straight in his chair. Before clamping his cell phone shut, he says "Semper Fi" to a buddy instead of "bye."

Barnes, a 58-year-old Marine veteran of Vietnam who earned a Purple Heart for wounds suffered during the 1968 Tet Offensive, is still military through and through. And he knows that in war, things happen "Boom!" — just like that — and triggers are pulled in split-second decisions.

That's why Barnes and fellow Vietnam veterans are starting a legal defense fund for Americans charged with war crimes in Iraq and Afghanistan.

"We're not concerned with guilt or innocence," he said. "We just want to make sure they have the best defense possible. Sitting here in Brockton or Quincy or New York or California, we don't know what happened."

Other similar defense funds have been sprung up. The mother of a Marine from New York who was cleared of murder charges created a fund, as did a group led by a retired Marine officer in Greensboro, N.C., who was twice wounded in Vietnam.

The funds have been set up in reaction to a series of cases in which U.S. servicemen have been charged with murder.

The Pentagon has contended that many of these cases do not involve split-second decisions made in the fog of war, but were deliberate, vengeful killings.

Among the major cases: Marines are under investigation on suspicion they deliberately killed 24 Iraqis civilians in a revenge attack after one of their own died in a roadside bombing Nov. 19 in Haditha, an insurgent stronghold in Iraq.

Separately, seven Marines are awaiting trial at Camp Pendleton, Calif., on charges of murdering an Iraqi last spring in Hamdania. Prosecutors said that Marines frustrated in the search for an insurgent dragged a civilian from his home, stuck him in a hole and shot him to death. They are accused of leaving a rifle and shovel nearby to make it look as if he had been caught digging a hole for a roadside bomb.

The Brockton veterans say they respect the Judge Advocate General Corps, the legal arm of the military, but fear the corps' young officers won't provide the best defense, especially against higher-ranking, experienced prosecutors. The defense fund would enable the servicemen to hire civilian defense attorneys if they want.

"I try more cases in a month than some guys try in their careers," Charles W. Gittins, a civilian lawyer who specializes in defending servicemen, said of JAG Corps lawyers.

The public affairs office at JAG headquarters did not immediately return calls. The Marine Corps Forces Central Command declined to comment.

Gittins defended Marine 2nd Lt. Ilario Pantano, who was cleared last year of murdering two Iraqi civilians in 2004. Pantano said he acted in self-defense. The case spurred Pantano's mother, Merry Pantano of New York, to create Defend the Defenders, which raises money to pay the legal costs of servicemen.

Larry Hutchins of Plymouth, whose son, Sgt. Lawrence G. Hutchins III, was charged in the Hamdania murder investigation, said he expects legal fees in his son's case could be $75,000. The bus repairman has hired a civilian defense attorney.

"He's my son. If it comes to remortgaging, or getting loans, we'll do whatever we have to do," he said.

"Obviously, there was an incident, and obviously there was a man killed," the father said. "But this is war. My son is a sergeant. He was a squad leader. He wasn't trained to make friends. He was trained to fight. I believe they were doing their job."

There are eight Purple Hearts among the eight Brockton-area men — seven of whom are former Marines who served in Vietnam — who created the Military Combat Defense Fund. They have raised $6,000 so far. Any U.S. military personnel charged in a violent crime in Iraq and Afghanistan is eligible.

Retired Marine Maj. Herbert W. Donahue Jr. started the Warrior Fund in June because he felt the "Pendleton 8" were being treated "worse than the detainees in Gitmo." About $20,000 has been raised, and three Pendleton families have petitioned for donations, said Donahue, who lives in Greensboro, N.C.

At least 14 U.S. servicemen have been convicted since 2003 on charges resulting from the deaths of Iraqis, according to information compiled by The Associated Press.

In Brockton, Barnes said he has extra incentive to watch out for troops. His son, a Marine, recently started his third tour in Iraq.

"What happens in war you just don't know," said the retired radio reporter, who suffered burns and shrapnel wounds in Hue City in 1968. "There may be more incidents of people acting out with less judgment than ought to be."