The retired Regimental Sergeant Major of the Army was one of dozens honoured at a commemorative service for Operation Hammersley in Canberra on Tuesday.

The 1970 battle left 12 Australians dead and 59 wounded, with an estimated 42 Viet Cong dead and more than 100 wounded.

Liberal senator and veteran Jim Molan told those gathered at the event the land mine was the weapon that defined Hammersley.

"At the highest levels of the army and in politics, the certainty of Australian deaths weighed more heavily than the chance of winning a hard-fought battlefield victory," Senator Molan said.

The men on the ground were constantly tense, with an army chaplain at the time saying the ground could erupt at any moment.

The operation was aimed at destroying a major enemy base in the Long Hai hills, a rugged part of South Vietnam which was riddled with Viet Cong tunnels.

"It was a sinister feeling place," Mr Rosemond said.

"Sounds funny, but it was dry and dusty but it was covered in vegetation and large rocks ... it wasn't good terrain for us."

At the time, Mr Rosemond was a 19-year-old corporal in charge of a tank and three other crew members. He had only been in Vietnam for two-and-a-half months.

"Would you give your 19-year-old your car?" Mr Rosemond said.

About 11 days into the operation his tank went over a land mine.

"In a split second everything went red, black and deafening," he said.

He bailed out his crew unharmed and was still on top of the tank when the ammunition inside ignited, sending flames five metres high.

Mr Rosemond now uses a hearing aid as a result of his near miss. He was lucky: on one day alone during Hammersley, land mines killed nine Australians and wounded 16 others.

Australians had cornered the Viet Cong, but were told to retreat for an aerial bombing run which took two days to arrive.

It gave the enemy plenty of time to escape, only for soldiers to go back in after the bombing to suffer more casualties.

"Well it's frustrating for us, because we knew we had them," Mr Rosemond said.

Hammersley seemed to provide little reward for Australians when it ended in March, it only raised public anger over repeatedly sending men into the deadly hills.

It took Mr Rosemond years to get over the land mine explosion, feeling guilty that he'd led his crew over the mine.

"There were times when I thought about it a lot," he said.

"I was feeling responsible that it was my decision. It wasn't my decision at all, I was doing what I was told to do.

"But at the same time I'm responsible to say, 'just move over to the right a bit, move to the left a bit' ... and I sort of questioned all of that. But now I just accept it."

Australian Associated Press