The Army said it still hasn’t fully fielded the country’s first hypersonic weapon, acknowledging a more than three-year delay in deploying the advanced technology that has the US lagging China and Russia.

The US Army’s program office said in a statement that it “continues fielding activities” for the long-range hypersonic missile known as the Dark Eagle and must complete additional training and other sustainment and operational-readiness activities “before declaring the system fully fielded.”The Army has already missed several previous deadlines to field the technology, including in 2023 and 2025. The Army’s top official for missile programs, Lieutenant General Frank Lozano also told Bloomberg in July that “we’ve been working through some quality defects” on the Lockheed Martin Corp. missile production line. Lockheed Martin didn’t immediately respond to a request for comment.

Lozano has said that accepting delivery of the remaining initial production run of missiles would depend on remedying the cause of those defects. He declined to provide an update when asked this week at an Army conference in Washington, DC.

With China and Russia already deploying new hypersonic projectiles, the absence of a similar US capability remains a major gap — and there’s growing pressure to field the system. Hypersonic missiles are able to fly low and extremely fast — more than 3,800 miles (6,120 kilometers) per hour — and are harder to intercept with traditional air defense systems.

The Dark Eagle delays underscore the Pentagon’s struggle to develop a homegrown hypersonic missile. Despite spending more than $12 billion since 2018, the US still lags China and Russia — which has already used deadly hypersonic missiles in its bombardment of Ukraine.

Also known as the Long-Range Hypersonic Weapon, or LRHW, the Dark Eagle has a reported range of more than 1,725 miles (2,776 kilometers), although its exact capabilities are secret. It is designed to glide to its target at more than five times the speed of sound, and can maneuver to avoid interception.

Army personnel have been practicing moving the Dark Eagle around Asia, testing how quickly its large launchers can be transported and positioned to fire, according to Lieutenant General Joel Vowell, the deputy commander of US Army Pacific.

The exercises are helping the service determine how to operate the long-range weapon across the vast region where US forces would need to avoid detection and quickly relocate to survive a potential conflict with China.

“We learned some good lessons,” Vowell said in an interview. He declined to identify where the Army had trained with the weapon, but said two Dark Eagle batteries have been established and are practicing movement throughout the Pacific theater.

He also declined to establish whether both batteries had their full complement of missiles, after units had dealt with delays in receiving the projectiles.

The Army expects to also eventually field additional hypersonic weapons on smaller, more widely deployed launchers such as the High Mobility Artillery Rocket System, he said.