Larry Heinemann, a Vietnam veteran who explored his lingering battlefield memories in two acclaimed novels, including “Paco’s Story,” which unexpectedly won the National Book Award in 1987, died Dec. 11 at a hospital in Bryan, Tex. He was 75.

The cause was chronic obstructive pulmonary disease, said his daughter, Sarah Heinemann.

Drafted into the Army in 1966, Mr. Heinemann was sent to Vietnam, where he saw combat while peering over the barrel of a .50-caliber machine gun. After a tour of duty with the 25th Infantry Division, he returned to his hometown of Chicago and studied writing, compelled to tell the world about what he had experienced.

“I was a soldier of the most ordinary kind and the war took much away from me,” he wrote in a 2005 foreword to a new edition of “Paco’s Story,” “but the war also gave me a story that simply would not be denied, as well as a way of looking at the world.”

At a time when other books about Vietnam, including Philip Caputo’s “A Rumor of War” and Tim O’Brien’s “Going After Cacciato,” were gaining wide recognition, Mr. Heinemann’s first novel, “Close Quarters” (1977), received little notice.

Described as “a first-person grunt’s-eye view of the Vietnam War” by novelist Ivan Gold in the New York Times, “Close Quarters” recounted a year in the life of an infantry unit, with all its drudgery, violence, brutality — and ever-present fear.

“It rains harder for a time, then slacks,” he wrote. “The moonlight dims and the rain picks up again. Then the not-quite-rain sound. Not the rustling of crickets and hares, not a night sound, but the stride of farmers, ploddish some, quick and silent some. Bare feet squeak in the grass. A silver and black shadow stands upright in the rain. . . . He fires.”

“Close Quarters” gained a certain gritty renown, literary scholar Gerald Nicosia wrote in 2005, and “was quickly discovered and treasured by a loyal coterie of combat vets for its graphic, down-and-dirty realism.”

In 1986, Mr. Heinemann published “Paco’s Story,” the pained saga of a badly wounded soldier, Paco Sullivan, returning from Vietnam as the sole survivor of an attack that killed everyone else in his unit. The novel follows Paco as he wanders the country, getting off a bus in Texas, where he works as a dishwasher, with his thoughts invariably returning to the horrors he witnessed in Vietnam.

The story, related by one of Paco’s ghostly fallen comrades, is addressed to an imaginary character referred to as James, whose only role is to listen in silence to the harrowing tale. The language is rough-hewn, profane and digressive, reflecting an attitude of cynicism and contempt toward authority of every kind. In one of his more lyrical passages, Mr. Heinemann wrote:

“And the next morning, in the bright, hot light of day, with the monsoon clouds clearing away to the west, the medic rose, stretched, and yawned . . . and he looked around, sour-faced, at the carnage and the ruin, the wreckage, at his fellows in Bravo Company (Which one of them will die today?). And, James, it was as if he saw the sheer, manifest ugliness — the blunt and pervasive, raw and stupefying ugliness — of that place for the first time.”

“Paco’s Story” was one of five finalists for the National Book Award for fiction, including Toni Morrison’s “Beloved” and Philip Roth’s “The Counterlife.” When Mr. Heinemann was announced as the winner, there was an awkward moment of stunned silence.

“This is an interesting surprise,” Mr. Heinemann said in accepting the award, which included a $10,000 check and a sculpture by Louise Nevelson. “I didn’t come here expecting to win.”

Several days later, New York Times critic Michiko Kakutani published a tartly worded essay, noting the “surprise and astonishment” of “the literary community” and suggesting that “Paco’s Story” was not in the same league as “Beloved.” A group of African American writers published a letter of protest in the Times, upset that Morrison had been overlooked. (Her novel was awarded the Pulitzer Prize several months later.)

“They can squawk all they want to,” Mr. Heinemann said. “I ain’t giving back the Nevelson and the $10,000 check has been cashed.”

Larry Curtis Heinemann was born Jan. 18, 1944, in Chicago. His father was a bus driver, his mother a homemaker.

Mr. Heinemann studied at a community college before serving in the Army. After coming back from Vietnam, he attended Columbia College Chicago, supporting himself as a bus driver before graduating in 1971.

“I became a writer because of the war,” he later said. “If not for Vietnam, I’d be driving a bus.”

Two of Mr. Heinemann’s brothers also served in the military during the Vietnam War. One of them vanished after returning from combat, and the other died by suicide.

“Everybody who came back knew that the war was a lie and that we had been betrayed and lied to,” Mr. Heinemann told the Los Angeles Times in 1988. “Basically we were used, wasted and dumped.”

He taught for 15 years at his alma mater, Columbia College Chicago, and in 1992 published a comic novel, “Cooler by the Lake,” that received lukewarm reviews. He received fellowships from the National Endowment for the Arts and the Guggenheim Foundation and studied Vietnamese folklore on a Fulbright fellowship in Hue, Vietnam.

Mr. Heinemann was a writer-in-residence at several colleges, including at Texas A&M University from 2005 until his retirement in 2015.

His 45-year marriage to the former Edie Smith ended in divorce. Survivors include his partner of several years, Kathy Favor of Bryan; two children from his marriage, Sarah Heinemann of Brooklyn and Preston Heinemann of Chicago; and a granddaughter.

In 2005, Mr. Heinemann published a memoir, “Black Virgin Mountain,” about his experiences in Vietnam and their lasting effect on his life.

“I arrived in Vietnam scared to death, and we were not pleasant people (down where the rubber met the road, so to speak) and the war was not a pleasant business,” he wrote. “I have no doubt we radicalized more southern Vietnamese to Ho Chi Minh’s nationalist revolution than we ‘saved.’ We understood perfectly well that we were the unwilling doing the unnecessary for the ungrateful.

“Like everyone else, I simply wanted out.”