Army Sgt. Sean M. Collins didn’t have to go to Afghanistan.

His father, Patrick, said his son had been to Iraq twice — most recently on a deployment last year.

"He could have claimed his dwell time. He could have said, ‘Look, I get a year (between deployments),’" Patrick Collins said. "In fact, he had to request a waiver to be able to deploy with his unit, but he was a team leader in an infantry platoon."

But Sean Collins knew it was his duty and responsibility to go, his father said.

The soldier with Hawaii ties was among six killed Sunday in Afghanistan when an explosives-packed minibus blew up at the entrance of a joint NATO-Afghan base in Kandahar province, the Pentagon said yesterday.

Collins, 25, who grew up in Washington state, and five of his fellow soldiers were killed in the deadliest attack on coalition troops this month.

The Department of Defense identified the other victims as Cpl. Willie A. McLawhorn Jr., 23, of Conway, N.C.; Spc. Patrick D. Deans, 22, of Orlando, Fla.; Spc. Kenneth E. Necochea Jr., 21, of San Diego; Spc. Derek T. Simonetta, 21, of Redwood City, Calif.; and Spc. Jorge E. Villacis, 24, of Sunrise, Fla.

They were with the 2nd Battalion, 502nd Infantry Regiment, 2nd Brigade Combat Team, 101st Airborne Division (Air Assault) out of Fort Campbell, Ky.

Collins’ father, a retired Army lieutenant colonel, lives in Palolo Valley. His son lived with him in Ewa Beach for about six months in late 2005 or early 2006 as he prepared to follow his father into the Army.

Sean Collins enlisted in the service, something his father said he had wanted to do from about age 5, in Honolulu.

Patrick Collins said his son had "a special unique Irish dark sense of humor — often vulgar, always totally politically incorrect — and it would still put a smile on your face."

Sean Collins was born in Colorado, and lived in Panama and Michigan before going through most of his "growing-up years" in Washington state, his father said.

Patrick Collins, a consultant for Booz Allen Hamilton at Fort Shafter, had deployed to Afghanistan in 2004-05.

The two would stay in touch through Facebook.

"It was a hard life. He was getting tired," Collins said. "He was looking forward to coming home. He was discussing whether he wanted to stay on in the service. He was debating the wisdom of having back-to-back combat tours, because it just wears you out."

Collins got the heartbreaking news on Sunday from his daughter while he was on assignment in Guam.

Collins said he felt "horrible, absolutely horrible." But he added, "I am incredibly proud of my son."