John W. Ripley, a highly decorated former colonel who entered Marine Corps lore when he single-handedly blunted a major North Vietnamese offensive during the Vietnam War by blowing up a strategically placed bridge, died Oct. 28 at his home in Annapolis, Md. He was 69.

The cause has not been determined, his son Stephen said.

Colonel Ripley, who at the time was a captain and a military adviser to a South Vietnamese Marine unit, blew up the southern end of the Dong Ha Bridge over the Cua Viet River on Easter Sunday, April 2, 1972. On the north side of the bridge, which was several miles south of the demilitarized zone, some 20,000 North Vietnamese troops and 200 tanks were poised to sweep into Quang Tri Province, which was sparsely defended.

Going back and forth for three hours while under fire, Captain Ripley swung hand over hand along the steel I-beams beneath the bridge, securing himself between girders and placing crates holding a total of 500 pounds of TNT in a diagonal line from one side of the structure to the other. The I-beam wings were just wide enough to form pathways along which he could slide the boxes.

When the boxes were in place on the bridge, Captain Ripley attached blasting caps to detonate the TNT, then connected them with a timed-fuse cord that eventually extended hundreds of feet.