A months-long investigation of a disastrous U.S. Special Operations mission that led to the deaths of four Americans in Niger found that “individual, organizational and institutional failures and deficiencies” contributed to an operation that spiraled out of control, citing improper planning by two junior officers but not placing blame on any single factor.

The Pentagon released an eight-page summary report Thursday, withholding thousands of pages of witness statements, maps and other documents and a longer report of about 180 pages. The U.S. military often releases those materials at the conclusion of an investigation, but said it is still working to declassify additional information.

The Pentagon also released a 10-minute video re-creation of the battle, but withheld a longer unclassified re-creation shown to family members and members of Congress this month.

The results were to be briefed to the news media Thursday by Marine Gen. Thomas D. Waldhauser, the chief of U.S. Africa Command, and Army Maj. Gen. Roger L. Cloutier Jr., his chief of staff. Cloutier led the investigation, in which 143 witnesses were interviewed, including one survivor of the attack who accompanied an investigative team to the battlefield.

The soldiers fought “courageously” after they were ambushed the morning of Oct. 4, but struggled with the overwhelming volume of fire they faced and the terrain, which included swamps, woods and open, dusty fields, U.S. military officials said. The unit included 12 American soldiers and more than 30 Nigeriens, and was attacked by about 100 militants linked with the Islamic State in the Greater Sahara (ISGS), the summary said. The American team was called Team Ouallam, after the location of a base they used.

The report follows months of conflicting accounts about what happened on the battlefield that day outside Tongo Tongo, a village less than 20 miles south of the border with Mali.

[Pentagon grapples with a thorny question after Niger ambush: What next in Africa?]

Killed in the battle were Staff Sgt. Jeremiah W. Johnson, 39; Staff Sgt. Bryan C. Black, 35; Staff Sgt. Dustin M. Wright, 29; and Sgt. La David T. Johnson, 25. Black and Wright were Special Forces soldiers, while both Johnsons were conventional soldiers assigned to the same 3rd Special Forces Group team.

At least five Nigerien soldiers also were killed, and other soldiers were wounded, including two Americans. They were identified in December as Capt. Michael Perozeni, the team commander, and Sgt. 1st Class Brent Bartels, in congressional testimony by David Trachtenberg, a senior defense official.

The militants initially attacked the U.S. patrol from the rear as its vehicles were moving south away Tongo Tongo while returning to their base in Niger’s capital of Niamey. The militants were armed with rifles, rocket-propelled grenades and vehicles mounted with machine guns.

The patrol began the previous day from Niamey, and was initially filed as a routine reconnaissance mission near Mali’s border by Perozeni and another Army captain planning it. No one higher in the chain of command was “aware of the true nature of the mission,” according to the Pentagon summary. In reality, it called for searching for Doundoun Cheffou, an Islamic State leader. The militant leader’s name is not included in the summary report, but has been published by The Washington Post and other media based on other reporting.

The ambush began about 11:40 a.m., with the first shots fired when the U.S. and Nigerien team were about 100 meters outside Tongo Tongo, the investigation found. The gunfire initially was light, but erupted as militants advanced through a wooded area to the south and east of the road on which the team was traveling. The team quickly reported contact with the enemy to U.S. soldiers at their base nearby, the summary said.

Believing they were facing a small enemy force, a handful of soldiers attempted to launch a counterattack on foot, but soon discovered a larger group of militants on motorcycles and in trucks mounted with machine guns. Assessing the severity of the situation, and seeing that some of the Nigerien troops had already fled, the Americans began to load their vehicles. 

A small group of soldiers — Black, Wright and Jeremiah Johnson — prepared to move out, but Black, trying to shield himself as he walked along the protected side of his vehicle, was quickly shot and fell, the investigation found. Wright and Johnson stopped the vehicle to assess Black’s wounds, but were forced to withdraw as the attack continued. Shortly afterward, Johnson was shot, then Wright. All three died quickly about noon, as they were overrun.

Unaware of what had befallen their comrades, other U.S. and Nigerien soldiers drove about 700 meters south, establishing a defensive position they hoped would allow them to fend off the advancing militant force. Perozeni, facing intensifying mortar and machine-gun fire, ordered a withdrawal.

Survivors told investigators that they saw one of the Americans on the scene, La David Johnson, preparing to get into a vehicle and drive away. The sergeant fought back using an M240 machine gun and a sniper rifle, but ultimately was forced out of his truck by enemy gunfire and tried to escape on foot.

U.S. military investigators estimated that the two nearby Nigerien soldiers were killed after running about 400 meters, and that Johnson ran an additional 450 meters southwest on his own, seeking refuge behind a thorny tree as he fired at the militants advancing toward him. U.S. officials think Johnson was killed about 12:30 or 12:45, about an hour after the ambush began. 

The other soldiers, meanwhile, were being pursued by militant forces as they tried to flee. Five of seven men in the car were shot, including Perozeni. After getting stuck in the mud, the troops radioed for assistance and then disabled that equipment. They fled enemy fire to the west through a swampy area, establishing a defensive position.

The bodies of Black, Wright and Jeremiah Johnson were retrieved a few hours after the firefight on the evening of Oct. 4. But the U.S. military was unable to recover La David Johnson’s remains until the evening of Oct. 6, an unusual amount of time to be missing on a modern battlefield.

U.S. military officials said Thursday that Johnson was not captured alive by militants or executed, but that he “was killed in action while actively engaging the enemy.” That assessment disputes previously reported accounts by Nigerien villagers. They told The Post in November that his hands appeared to have been tied behind his back.

Johnson’s missing remains triggered the declaration of what the Pentagon calls a DUSTWUN, which stands for “duty status whereabouts unknown,” U.S. military officials told The Post in October. Members of the elite Joint Special Operations Command (JSOC) were ordered to assist in the search, the officials said, although it wasn’t clear whether they participated.

Gen. Joseph F. Dunford Jr., the chairman of the Joint Chiefs of Staff, appeared to allude to the deployment of JSOC in October, telling reporters at the Pentagon that “national assets” were made available for the search after a request from Waldhauser. The deployment indicated that it is likely that U.S. military officials were not certain the evening of Oct. 4 whether La David Johnson was dead, or captured alive, officials said at the time.

Defense Secretary Jim Mattis defended other U.S. troops involved in the battle, suggesting that extenuating circumstances led to the struggle to recover Johnson’s remains.

“The U.S. military does not leave its troops behind, and I would just ask you not to question the actions of the troops who were caught in the firefight and whether they did everything they could in order bring everyone out at once,” Mattis said Oct. 19.

The events generated an immediate outcry from lawmakers, who said that they had not been properly informed about military activities in Niger, and potentially beyond. 

The episode ignited a larger political controversy after a Democratic congresswoman reported that President Trump had upset La David Johnson’s widow in a condolence call, saying that the president had stumbled over the soldier’s name and that he suggested that the soldier “must have known what he signed up for.”

Trump denied the account, and his chief of staff, John Kelly, blasted the lawmaker, Rep. Frederica S. Wilson (D-Fla.). Kelly, whose own son was killed in the war in Afghanistan, called Wilson an “empty barrel” and made a subsequently disproved claim that she had improperly taken credit for funding an FBI facility in Florida. 

The controversy was a departure from how previous administrations handled military casualties, and provided another illustration of how Trump has been willing to feud publicly, even with individuals typically seen as beyond reproach. 

Johnson’s mother later corroborated Wilson’s account of the conversation and said the president “did disrespect my son.” 

Alex Horton and Paul Sonne contributed to this report.