The U.S. Air Force has accepted the first Boeing KC--46A aerial refueling tanker aircraft and the "milestone delivery" to the McConnell Air Force Base in the Midwestern state of Kansas will be made in a few weeks, U.S. aircraft manufacturer Boeing Company said Thursday.

Boeing said the first four of the KC-46A Pegasus tankers will be delivered to the McConnell base by the end of the month, while the other four aircraft of the same type will reach Oklahoma's Altus Air Force Base in early February.

Boeing is on contract for 52 of an expected 179 tankers for the Air Force, and Thursday's delivery has been delayed for two years, which has cost Boeing a total of 3 billion U.S. dollars for the KC-46 tanker program.

The top U.S. aircraft manufacturer said that besides the first refueling plane accepted Thursday, nine aircraft are undergoing customer acceptance testing with the remaining aircraft of the contracted amount in production.

The KC-46 tanker was made from the airframe of Boeing's commercial 767 jet and built in Boeing's facility in Everett, Washington state.

"The KC-46A is a proven, safe, multi-mission aircraft that will transform aerial refueling and mobility operations for decades to come," said Leanne Caret, president and CEO of Boeing Defense, Space and Security.