Army personnel in Hawai'i yesterday completed destruction of the largest concentration of unexploded, or "dud," chemical rounds ever found in the United States.

The destruction of 71 chemical munitions at Schofield Barracks began in April, but was halted for system maintenance in May after 65 were safely destroyed.

Two of the remaining six were destroyed Wednesday, the Army said in a news release, and the other four were exploded yesterday morning.

Air monitoring confirmed there was no release and that the munitions, including their chemical fill, were completely destroyed, Army officials said.

The munitions were phosgene and chloropicrin rounds manufactured from World War I. The rounds were stockpiled through WWII, the Army said in April. The munitions were discovered from 2004 to 2006 during an ordnance cleanup of an old range for a Stryker brigade "battle area complex."

Included in the chemical weapons were 155 mm artillery shells. The cleanup cost $7 million, the Army said.

Detonation technology called the Transportable Detonation Chamber TC-60 was used to destroy the munitions. The TDC will now be disassembled and returned to the Mainland for future destruction operations, the Army said.