A U.S. Army Apache attack helicopter crashed early Saturday while flying a routine training mission at the National Training Center at Fort Irwin in California, leaving the pilot and copilot dead.

“The cause is currently under investigation and next-of-kin notifications are ongoing, therefore we can provide no further details at this time,” Lt. Col. Jason S. Brown, a spokesman for the Army at the Pentagon said in a statement to Fox News.

A separate official reported that the Apache helicopter, which was attached to the Army’s 4th Infantry Division based in Fort Carson, Colorado, was participating in a “readiness training exercise” at the time of the crash. The helicopter had been deployed to California as part of a regular training rotation that occurs in the California desert.

The AH-64 Apache helicopter is equipped with hellfire missiles, rocket pods and a 30mm chain gun.

In November testimony before Congress, the head of Army aviation, Maj. Gen. William Gayler, said that the flight hours of his pilots were at their lowest levels in 30 years due to years of military budget cuts.

Defense Secretary Jim Mattis delivered a speech Friday at the Johns Hopkins School of Advanced International Studies in Washington, D.C., in which he said that the United States military’s advantage over Russia and China has “eroded.” Mattis cited budget cuts and more than 16 years of continuous combat by the U.S. as factors contributing to the erosion, while Beijing and Moscow modernized their forces.

“For too long, we have asked our military to stoically carry a ‘success at any cost’ attitude as they work tirelessly to accomplish the mission with now inadequate and misaligned resources, simply because the Congress could not maintain regular order,” Mattis said.

Mattis warned that, with no budget, U.S. military units will be deprived of valuable training opportunities, “aircraft will remain on the ground, their pilots not at the sharpest edge.”

In 2017, twice as many U.S. troops were killed in non-combat aviation crashes compared to the year before. Saturday’s helicopter crash was the first known fatal accident for the U.S. military in 2018.