Bill Green arrived in Vietnam two weeks before the 1968 Tet Offensive — 50 years ago Jan. 30. Assigned to the 198th light infantry, he was being trained on map reading and booby traps at the Americal Division in Chu Lai.

“(Enemy) rockets started coming in,” said Green, an Alamo resident and president of the Vietnam Veterans of Diablo Valley. “They finally ignited the ammo dump. When the ammo went off it was like the sun came up. It got super bright. All I could see was a big mushroom-shaped cloud and I said, ‘Holy (expletive), they dropped the bomb. They waited until I got here to drop the bomb.'”

So the Tet Offensive was a surprise?

“Uh, yeah,” Green said.

The Tet Offensive, unleashed during the Vietnamese lunar new year holiday, changed everything. Before Tet, Gen. William Westmoreland,  commander of U.S. troops in Vietnam, stated, “We have reached a point (in the war) where the end comes into view.”

President Lyndon Johnson seemed buoyant when he visited the troops in South Vietnam shortly before Christmas 1967.

“The enemy is not beaten,” Johnson said, “but he knows that he has met his master in the field.”

Before Tet, North Vietnamese forces engaged U.S. troops in the countryside, in forests and rice paddies. Initiating surprise attacks in the cities of South Vietnam was a bold, all-in move, one the North hoped would demoralize the enemy, perhaps to the extent that the Americans would give up and go home.

Steve Thompson, a Navy corpsman assigned to the Marines, saw the beginning of the Tet Offensive. He didn’t know it at the time.

“Part of my job was reconnaissance, to go on patrols to various areas north of Dong Ha,” said Thompson, 70, of San Jose. “Starting in January, we saw troop movements around Dong Ha. South of the DMZ we started to see troop movements. I guess that was the buildup to Tet.”

Fighting was intense. The Marine garrison at Khe Sanh was under siege for 77 days. Cities such as Hue and Ben Tre were virtually obliterated. Soldiers from the north bombed the Marine base at Da Nang and penetrated the U.S. Embassy in Saigon. The Tet Offensive was war on a grand scale. But there were plenty of small, desperate battles.

“We were on patrol in the middle of February of 1968, out near Con Thien,” Thompson said. “We encountered a larger movement of troops. We were surrounded by almost a small battalion of Viet Cong. We engaged with the enemy. There were eight of us. Five guys were killed that day. At the time all I knew was there was a lot going on and I was treating the wounded. The lieutenant who led the patrol received the Medal of Honor.”

Thompson was awarded the Silver Star.

Fighting commenced shortly after midnight on Jan. 30 in Pleiku, where Cang Dong, a member of the Vietnam Armed Forces, was stationed. Combatants from the north moved toward the city.

“They hit right on the night we were supposed to have an agreement with them, a cease fire for the new year,” said Dong, 70, who immigrated to San Jose in 1990.

“We had some casualties, three or four in my company,” he said. “We killed almost 50 of them. The reason we can kill them a lot like that is because we were armed with heavy tanks and more ammunition. The saboteurs only carried one or two magazines.”

Dong wasn’t altogether surprised by the offensive — “You never can trust the Communists” — but he was startled to see U.S. soldiers, apparently on alert, but taking no action.

“They probably had orders from the camp commander,” said Dong, president of the local chapter of Associates of Vietnam Veterans of America. “They don’t do nothing. They just stayed where they were. Our people heard rumors that the reason the Americans did not interfere was they wanted to see if our people had the capabilities to take over the war from them.”

Both sides were scarred by the Tet Offensive. TV newscasts beamed same-day reports from the fighting into America’s living rooms. They didn’t conform to Westmoreland’s optimistic assessment. And they weren’t pretty: A South Vietnamese general executing a prisoner of war with a bullet to the head; an American officer addressing the devastation in Ben Tre by saying, “It became necessary to destroy the town to save it”; and trusted anchorman Walter Cronkite telling viewers, “The only rational way out (of the war) will be to negotiate.”

Meanwhile, the North’s all-in strategy failed. The North Vietnamese were unable to hold the targets of value captured early in the offensive, were unsuccessful in their goal of liberating the South, and sustained tremendous casualties.

Two months after Tet, a besieged Johnson announced he would not run for another term as president. Two months after that, North Vietnam diplomats attended peace talks in Paris for the first time.

It took five years for the last U.S. troops to leave Vietnam, and just two years after that for the North Vietnamese to overrun the South.