Two U.S. military KC-130 air refueling tankers arrived Tuesday at the U.S. Marine Corps Air Station Iwakuni in Yamaguchi Prefecture in the first transfer under a bilateral agreement to reduce the burden on Okinawa of hosting U.S. bases.

The long-delayed transfer will bring a total of 15 KC-130s to Iwakuni by the end of August, along with approximately 870 U.S. military personnel and their family members, according to the Iwakuni air station. It is the first time U.S. units have been moved from Okinawa to another area in Japan.

The U.S. military has said it will fly the KC-130s based in Iwakuni to Okinawa to conduct exercises in coordination with U.S. Marines there as necessary, throwing into question how much the step will actually help reduce the burden of the military presence in Okinawa, home to the bulk of U.S. bases in Japan.