At the Battle of Dak To, the sky was crowded overhead. In addition to the Marine A-4s, a pair of Air Force A-1 Skyraiders was dropping napalm — intending both to kill North Vietnamese troops and to create fires on the ground that the pilots in faster A-4s could use as reference points for follow-on bombing runs. B-52s were approaching with plans to carpet-bomb. An AC-47 gunship was circling. The job of coordinating all these varied options and attacks fell to Capt. James E. Wrenn of the Air Force, who was flying a small Cessna propeller plane.

Lt. Col. Richard Taber, the pilot who the report indicated dropped the bombs, had flown 90 hours in combat since arriving in Vietnam roughly three months before. Taber flew with the call sign Hellborne 526-1 and commanded a Marine Corps A-4 squadron in Chu Lai. He was supposed to drop his bombs directly onto one of the napalm fires, but his bombs fell about 650 feet short and to the right, a miss the investigator labeled “a short round.” It landed on Charlie Company, Cook’s sister unit, which he had fallen in with amid the chaos of the fighting.

How this mistake occurred remains unclear. The report said the A-4 may have approached the target area from a direction slightly off axis from what Wrenn directed, resulting in the bombs landing downslope from the intended target. But the investigation was ultimately inconclusive, declaring that “there is insufficient evidence to determine the exact cause of the short round” before blaming “improper release conditions.” The investigator recommended that pilots undergo remedial training and that the investigation be closed, as it had revealed “no gross personnel errors nor evidence of equipment malfunction.”

Today, Cook, who is now 72, lives in Azusa, Calif., and spends his days tending to his grandchildren nearby. Dak To, he said, is never far from his thoughts. “Not a day goes by that I don’t” think about it, Cook said. “I’ve always thought about it, but to actually share it with others, that took 35 or 37 years.” In March 2017, Cook returned to Hill 875 to help look for the remains of the three American soldiers who had never been recovered: Sgt. Donald Iandoli, Specialist Jack L. Croxdale II and Pfc. Benjamin David De Herrera. The mission did not find the missing men, and Cook surmises that their bodies were vaporized in the blast. But Cook’s participation in the search connected him with a military investigator who was also on the trip. “I mentioned that I wondered what the pilot felt, knowing that he was responsible,” Cook said. “It must have been hard for him to carry on.” The investigator’s answer surprised him. “If you read the report,” Cook recalled being told, “you might have a different opinion.”

Cook subsequently obtained a copy of the report in 2017, which, as far as he knew, had never been publicly released. A scholar who wrote about the fight for Hill 875 in the 1980s and an author who wrote a book about it in the 1990s both told The New York Times that they had never seen the report before, even after searching through files related to the battle in the National Archives. Upon reading it, Cook found that instead of taking responsibility, the Marine pilot’s statement to investigators criticized almost everyone but himself and his wingman. Taber blamed other pilots for being unprofessional over the radio, spoke of one pilot’s “imperious manner” and called out others for being sarcastic and impatient. He did, though, praise his own skills. “I have been dropping Snakeyes exclusively in my last 15 or 20 launches from the alert,” his statement reads. “I can recall no reported miss distance as great as 50 meters in range, and nothing approaching that in azimuth.”