U.S. Army officials say 560 shells and bottles containing mustard agent have been destroyed in the first round of a project to eliminate the nation's largest remaining stockpile of the chemical.
The first phase ended Thursday at the Pueblo Chemical Depot in Colorado.
A partially automated plant will disassemble and neutralize another 780,000 shells containing 2,600 U.S. tons of mustard agent starting this spring and finishing in 2019.
The first phase used explosives in a closed chamber to destroy bottles and leaking or damaged shells. They were considered unsuitable for the plant.
Another 523 tons of mustard and nerve agents are are awaiting destruction at the Blue Grass Army Depot in Kentucky. Work there is expected to start this year or next.
The weapons are being destroyed under international treaty.