TOKYO — U.S. Forces Japan commander Lt. Gen. Thomas C. Waskow told media Thursday that the United States did everything it should in the investigation of a recent helicopter crash and reiterated the importance of strong security cooperation between the United States and Japan.

Much of Waskow’s speech at the Japan National Press Club focused on the Aug. 13 crash on Okinawa of a U.S. Marine Corps CH-53D Sea Stallion helicopter that clipped a university building during an emergency landing.

Okinawan officials have criticized U.S. forces for excluding them from the investigation and closing off the crash site; media reports on the island also speculated several coverups by U.S. personnel.

Waskow said U.S. forces did what they were supposed to when they sealed the crash site, to safeguard the safety of civilians nearby and the overall investigation.

“Our response was conducted precisely within the confines of the agreements we have with the government of Japan and our own internal military guidance,” he said. “Despite some press reporting to the contrary, I would like to assure you that the U.S. has cooperated totally with local authorities throughout the entire process.”

After an accident, the military conducts an immediate safety inspection to determine a cause, he said, followed by a detailed investigation into all other possible factors.

On Okinawa, Marine Corps leaders determined the crash was caused by a faulty part, and they briefly grounded all helicopters. After the investigation determined the defect was restricted to the individual aircraft, other helicopters resumed flights.

Sea Stallions were grounded until the Department of Defense deployed some of them to Iraq; the rest remain grounded until the investigation is complete.

Waskow said investigators will give Japan a full report on the accident after the investigation closes. The detailed investigation should take about 30 days.

The general said he hoped to dispel some rumors surrounding the crash. He categorically denied reports that the helicopter was carrying depleted uranium or that any substance, including oil-tainted soil, was thrown into the sea.

Waskow, who heads a command of 58,000 servicemembers in Japan, also discussed the transformation of the U.S. military. He said as the United States transforms its force posture, some change is likely in Japan. But changes will require approval by both nations and will support the best interests of both.

Waskow said leaders of both nations have been discussing changes for a year and a half.

“Taken together in all its strength and vitality, the Japan- U.S. security relationship is the centerpiece of our security architecture in the Pacific-Asia region,” he said. “The U.S. is in no way changing its commitment to the defense of Japan or any of our friends and allies around the world.”

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