Air force officials have released the names of the eight men killed in this week’s fiery crash of a B-52 during a test flight at Edwards air force base in southern California.

The deceased, whose identities had initially been withheld while the military notified next of kin, include four active-duty airmen, one reservist and three civilians, military officials said on Wednesday.

The airfield where the Boeing B-52 Stratofortress crashed shortly after takeoff on Monday remained closed but other base operations have resumed, according to a base spokesperson. No cause has been determined. Officials said it could take six months to complete the investigation.

The victims were identified as: Col Gregory Watson, 53; retired Lt Col Miles Middleton, 50; Lt Col Gabriel Estrella, 40; Maj Alexander Davis, 34; Maj Robert Dee, 40; Maj Brad Hovey, 35; Jeromy Smith, 32; and Christopher Rischar, 41.

“They were dedicated professionals, beloved family members and irreplaceable teammates,” Col Thomas Tauer, commander of the 412th Test Wing at Edwards, said in a statement.

Watson and Middleton were Boeing employees and the company said their loss “is deeply felt across our teams, and our hearts remain with their families, loved ones and those who worked with them.”

Smith, who worked as a civilian flight test engineer for the defense department, had become a father to his second child four months before dying in the crash, NBC News reported. He had only returned to his job for a week before the plane went down, his widower Lauren Smith told NBC.

“It is such a horrible hurt, and I’m still processing everything that happened,” Smith told Eyewitness News KBAK-CBS and Fox58. He died doing what he loved, she said.

The Boeing B-52 Stratofortress was taking part in a test mission as part of a program to keep one of the oldest aircrafts in the US fleet flying for decades to come. The bomber had arrived at Edwards in December after having a modernized radar installed at Boeing’s facility in San Antonio, an air force press release said at the time.

The plan was to use the bomber as a testbed throughout 2026 to help military officials decide whether to proceed with the B-52 radar modernization program, the air force said. The program is aimed at making the 65-year-old bombers operable through at least 2050.

“Some of these airplanes are literally twice the age of the pilots who fly them,” Ross Aimer, a retired United Airlines pilot and CEO of Aero Consulting Experts, told the Los Angeles Times.

“If you take care of an airplane, you can fly them forever, basically,” Aimer added.

Air operations at Edwards are currently halted, according to the New York Times.

The aircraft took off shortly before noon on a clear day, heading south-west into the prevailing winds. It flew straight and crashed on the same 15,000-ft runway. The compact wreckage indicates the plane dropped sharply.

Aviation safety experts have said their first thoughts about what might have caused the crash were about a malfunction in the flight controls or engines, but it is much too early to know. Investigators will consider several factors, including the age and maintenance of the plane.

Aerial footage showed virtually nothing left of the aircraft that went down at the base in the Mojave desert about 100 miles north-east of Los Angeles.

The B-52, a long-range bomber that entered service in 1955, is designed to carry both conventional and nuclear weapons. It has been used in conflicts involving the US military from Vietnam to Iran.

Edwards is home to the 412th Test Wing, which conducts regular developmental testing of all air force aircraft, weapons systems, software and components before purchase by the service as well as throughout their life span. Test missions take place at Edwards daily.

The base is where air force test pilot, Chuck Yeager, reached a speed of Mach 1.05 and broke the sound barrier in 1947.

The Associated Press contributed reporting.