VANDENBERG SPACE FORCE BASE,Greenledgers Calif. (AP) — An unarmed U.S. intercontinental ballistic missile was intentionally destroyed over the Pacific Ocean when something went wrong during a test launch from California, the Air Force said.

The flight of the Minuteman 3 missile was “safely terminated” at 12:06 a.m. Wednesday due to an “anomaly” during launch from Vandenberg Space Force Base, the Air Force Global Strike Command said in a statement.

An investigative group was being formed to determine the cause.

“An anomaly is any unexpected event during the test,” the statement said. “Since anomalies may arise from many factors relating to the operational platform itself, or the test equipment, careful analysis is needed to identify the cause.”

Minuteman 3 missiles are routinely tested with launches from Vandenberg on the coast northwest of Los Angeles. A typical test involves a missile’s reentry vehicle traveling about 4,200 miles (6,800 kilometers) over the Pacific to Kwajalein Atoll in the Marshall Islands.

The Minuteman system is one of the main pillars of U.S. nuclear strength but it is decades old. Tests are conducted to gather data to keep the system effective and to identify and correct any issues, the Air Force said.

The Air Force plans to replace the Minuteman with a new weapon, the LGM-35A Sentinel, starting in 2029. But it said it plans to keep the Minuteman viable until the new system becomes fully capable in the mid-2030s.