Hundreds of former commanders and military colleagues of presumptive Democratic nominee John Kerry are set to declare in a signed letter that he is "unfit to be commander-in-chief." They will do so at a press conference in Washington on Tuesday.

"What is going to happen on Tuesday is an event that is really historical in dimension," John O'Neill, a Vietnam veteran who served in the Navy as a PCF (Patrol Craft Fast) boat commander, told CNSNews.com. The event, which is expected to draw about 25 of the letter-signers, is being organized by a newly formed group called Swift Boat Veterans for Truth.

"We have 19 of 23 officers who served with [Kerry]. We have every commanding officer he ever had in Vietnam. They all signed a letter that says he is unfit to be commander-in-chief," O'Neill said.

O'Neill, currently a Houston, Texas, based attorney, is no stranger to Kerry. O'Neill served in the same naval unit as Kerry and commanded Kerry's swift boat after Kerry returned to the United States. Kerry's command of the PCF boat lasted four months and ended shortly after he received his third Purple Heart. According to naval regulations at the time, any sailor who received three Purple Hearts could request a transfer out of the combat zone.

Kerry and O'Neill engaged in a nationally televised debate in 1971 on The Dick Cavett Show over Kerry's allegations that many Vietnam soldiers had routinely engaged in atrocities such as raping and cutting off ears and heads of Vietnamese soldiers and citizens. Kerry was the then spokesman for the anti-war group Vietnam Veterans Against the War.

"We are going to be presenting a letter that deals with Kerry's unfitness to be commander and chief that has been signed by hundreds of swift boat sailors, including most of those who served with Kerry," O'Neill explained.

"The ranks of the people signing [the letter] range from admiral down to seaman, and they run across the entire spectrum of politics, specialties, and political feelings about the Vietnam War," he added.

Among those scheduled to attend the event at the National Press Club and declare Kerry unfit for the role of commander-in-chief are retired Naval Rear Admiral Roy Hoffman, who was the commander of the Navy Coastal Surveillance Force, which included the swift boats on which Kerry served.

Also scheduled to be present at the event is Kerry's former commanding officer, Lt. Commander Grant Hibbard. Hibbard recently questioned whether Kerry deserved the first of his three Purple Hearts that he received in Vietnam. Hibbard doubted both the severity of the wound and whether it resulted from enemy fire.