OKLAHOMA CITY (AP) — The Oklahoma National Guard’s last Vietnam veteran is retiring this month after dedicating more than four decades to the Army.

Chief Warrant Officer 5 Ronald Petty, 61, has served in active duty, reserves and the National Guard.

“His positive attitude and enthusiasm will be missed,” Brig. Gen. Robbie Asher, chief of the Guard’s joint staff, told The Oklahoman. “Throughout his career, Chief Petty has always been a positive, proactive and highly professional soldier who never faced a challenge he could not overcome.”

Petty first joined the military in 1969 at age 18.

“It was the G.I. Bill that got me to join,” Petty told The Oklahoman.

He headed overseas, spending 16 months mostly in Cambodia, working alongside South Vietnamese counterparts.

“On patrol we would carry several hundred rounds of ammunition and two water canteens,” Petty said. “Thankfully, no one from my team was killed while we were over there. We still exchange Christmas cards and emails.”

Petty went to college after his tour and earned a managing and marketing degree. He joined the National Guard in 1975, left the Guard twice but missed it and came back.

Petty eventually took a job in the Guard’s personnel division at Camp Gruber near Braggs, where his sons grew up. His oldest boy, Eric, joined the Army out of high school and had nearly 10 years in the service by the time the war in Iraq began. He volunteered for deployment and was killed in battle a day before his 29th birthday.

Ronald Petty said dealing with his son’s death was difficult, in part because Eric left behind a 9-year-old son, Colton.

“The casualties in this war are acceptable from a military standpoint,” Ronald Petty said. “It’s nothing like Vietnam, where we were losing thousands of soldiers every year. But when it’s your son, it’s different.”

Eight years later, Colton is now 17. He has joined the Guard and will finish advanced training after he graduates from high school in May.