A B-1B Lancer bomber flies over Afghanistan in November 2013. A Lancer was involved in a friendly fire airstrike that killed five U.S. troops and an Afghan soldier in June. (U.S. Air Force Photo/Master Sgt. Ben Bloker)

A friendly fire incident in Afghanistan that killed U.S. Special Forces and other American soldiers, along with an Afghan soldier, was the result of poor communication, inadequate planning and several other mistakes, according to the results of a U.S. military investigation released Thursday.

The June 9, 2014, airstrike marked one of the ugliest friendly fire incidents in more than 12 years of U.S. military operations in Afghanistan. A B-1B Lancer bomber dropped its ordnance on five U.S. soldiers, including members of an elite Special Forces team.

“The key members executing the close air support mission collectively failed to effectively execute the fundamentals, which resulted in poor situational awareness and improper target identification,” the investigating officer, Air Force Maj. Gen. Jeffrey L. Harrigian, said in his report. “While this complex combat situation presented a challenging set of circumstances, had the team understood their system’s capabilities, executed standard tactics, techniques and procedures and communicated effectively, this tragic incident was avoidable.”

Americans killed include Staff Sgt. Scott R. Studenmund, 24; Staff Sgt. Jason A. McDonald, 28; Spc. Justin R. Helton, 25; Cpl. Justin R. Clouse, 22; and Pvt. Aaron S. Toppen; 19. An Afghan army sergeant, Gulbuddin Ghulam Sakhi, also was fatally wounded by the bomb, according to the investigation report. McDonald and Studenmund were Special Operations troops with the 5th Special Forces Group of Fort Campbell, Ky., while Helton was a bomb technician and Clouse and Toppen were infantrymen.

The final investigation report, dated Aug. 5, describes confusion between the crew in the Air Force bomber and the leaders of the mission on the ground, which was launched in Zabul province to disrupt the Taliban and improve security in the Gaza Valley and Zabul’s Arghandab district. The situation spiraled quickly as the troops came under insurgent gunfire while waiting for helicopters to extract them near the end of the operation, the report said.

This photograph shows the area of Afghanistan where five U.S. troops and an Afghan soldier were killed in a friendly fire airstrike by a B-1B bomber on June 9, 2014. The image was edited by the U.S. military because of what it described as operational security. (Photo released by U.S. Central Command)

Significantly, the soldiers who were later killed by the airstrike maneuvered up a hill after taking enemy fire without it being understood by the U.S. commander on the ground, an Army captain, or the joint terminal attack controller (JTAC), whose job is to communicate with fighter jets and bombers to ensure the right targets are hit. The miscommunication resulted in other U.S. troops believing that muzzle flashes they saw from the Americans’ weapons marked the location of insurgents, the investigation found.

There were numerous other problems. All key leaders in the mission, including the ground commander, JTAC and air crew, thought that sensors on the bomber would be able to see infrared strobe markers. The targeting pod on the B-1B bomber cannot do that, leading the air crew to incorrectly believe there were not troops on the ridgeline they bombed, investigators determined.

Troops on the ground directing the airstrike repeatedly told the B-1B crew that all friendly troops were 300 meters away from the ridgeline about to be targeted. The bombs were dropped shortly after 8:24 p.m., and almost immediately questions were raised about whether a fatal mistake had been made. Soldiers at the base of the ridgeline reported that the bombs had hit “our hill,” and survivors scrambled to the site to check.

“All personnel were conducting their assigned tasks,” another Special Forces member told investigators, according to a copy of his witness statement included in the report. “I assumed the enemy was maneuvering, but I told my guys to stay put and make sure they had their strobes on. My understanding was that all my guys had strobes on and that the aircraft had identified guys without strobes on. It was clear to me that it had been relayed to aircraft that that there were American elements with [infrared] strobes on.”

A member of the Air Force crew, interviewed June 27 at a U.S. Central Command facility at Udeid Air Base in Qatar, said it was hard to communicate with the troops on the ground with radios, but they were clear that the JTAC wanted two bombs dropped on the hill.

“The JTAC’s focus on IR strobes was moer [sic] than normal, but I’m not going to question the JTAC in a situation like this,” the B-1B crew member said. “I can hear the stress in his voice and see… the [targeting] pod, so given the comms condition I’m not going to waste precious time questioning the information the JTAC is passing.”

Friendly Fire Airstrike in the Vicinity of Arghandab, Afghanistan, 9 Jun 14 by Dan Lamothe