The new planes bring the total number of Ospreys to be stationed at the base to 24 even as local opposition in Okinawa remains due to safety concerns, Kyodo News reported.
The new Ospreys, which are capable of vertical takeoff and landing like a helicopter but fly like a plane, arrived at the U.S. military's Iwakuni base in western Japan, where they will be flight-tested for a week before being deployed in Okinawa, the Japan Defense Ministry said.
The Ospreys will replace aging CH-46 helicopters in Okinawa, Kyodo said.
However, the report said Okinawa Gov. Hirokazu Nakaima, reacting to local public opposition, has urged the planes not be stationed on the island because of its history of crashes.
Kyodo said the U.S. military allowed reporters into the Iwakuni base to see the planes' offloading process. U.S. officials have said the Ospreys will contribute to security in the Asia-Pacific region.
The local opposition is also tied to calls for relocating the Futenma air station out of Okinawa.
Japanese Chief Cabinet Secretary Yoshihide Suga assured the government will work closely with Washington to ensure safe operations.
Japan is the United States' closest ally in Asia and the new government of Prime Minister Shinzo Abe wants to strengthen the ties with Washington amid China's growing military might.
Last week, Japan's Defense Ministry, in an interim report, called for strengthening the country's defense capabilities, saying the "national security environment that Japan faces has become more serious."
The report proposed that Japan strengthen the marine functions of the Self-Defense Forces and prepare troops for a quick dispatch to remote islands. Currently Japan is locked in a tense territorial dispute with China over the Senkaku Islands in the East China Sea, which Beijing also claims.
The MV-22 Osprey is seen as an option to meeting the ministry's proposal.
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