Army Lieutenant General Patrick O'Reilly, who has headed the Pentagon arm since November 2008, demeaned and belittled subordinates, making them reluctant "to speak up and raise issues during meetings with him," said the 19-page report dated May 2.
The agency is developing, testing and fielding a layered shield against ballistic missiles that could be fired by countries like Iran and North Korea, Reuters reports.
It manages research, development, testing, purchases and stitching together complex systems on land, at sea and sensors in space.
The $10 billion-a-year effort has a long record of flight-test failures and successes as well as the biggest research budget of any Pentagon program. Some critics have derided it as a boondoggle for contractors including Lockheed Martin Corp, Boeing Co, Raytheon Co and Northrop Grumman Corp.
The inspector general interviewed O'Reilly and 33 other witnesses with knowledge of the matters at issue for a preliminary report. Another four were added at O'Reilly's request, but they were not in a position to comment on certain events at issue, the report said.
Several witnesses testified that fear of O'Reilly's reactions "impeded the flow of information," the investigation found. It was first reported by The Cable, a web-based newsletter of Foreign Policy magazine.
A spokeswoman for the inspector general, Bridget Serchak, said such reports typically were made public only after receipt of at least three requests for them under the Freedom of Information Act.
The report said five witnesses told inspectors that O'Reilly's leadership, described by the investigators as marked by yelling and screaming, was either the main factor or a contributing factor in their decision to leave the agency.
"We received consistent testimony that as a result of his management style, even senior officials stopped communicating" with O'Reilly, the report said.
The inspector general recommended the secretary of the army consider "appropriate corrective action" with regard to O'Reilly. Army representatives did not return phones calls seeking comment.
O'Reilly, in a response summarized in the final report, questioned the accuracy of witness testimony and denied engaging in many of the alleged brow-beating practices.
He stated that he had initiated weekly meetings with top aides to make sure that effective lines of communication stayed open. Richard Lehner, a spokesman for the Missile Defense Agency, had no comment on the report.
A majority of the witnesses testified that O'Reilly was highly intelligent, "even brilliant," and possessed a high degree of expertise in managing purchases, the report said.
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