The U.S. Air Force is a step closer to getting its first next-generation KC-46A aerial refueling tanker after production of the aircraft began this week, the Boeing Company (NYSE:BA) said in a statement released on Thursday.

“Completing production of the four test aircraft on schedule is our priority as we prepare to enter the flight test phase of the program,” said Maj. Gen. John Thompson, the U.S. Air Force Program Executive Officer for Tankers. “The program continues to meet or exceed all contract milestones.”

The first test aircraft is expected to roll out of the factory in January of 2014, and the second test aircraft is expected to leave the factory in March.

Boeing’s Vice President, Maureen Dougherty, said the production of the tanker is on schedule and in a year from now all four test aircraft will be out of the factory.

The tanker is modeled on Boeing’s 767 commercial jetliner and is intended to replace the U.S. Air Force’s aging fleet of KC-135 Stratotankers, which has been the primary refueling aircraft for more than 50 years. The initial flight of the air tanker is scheduled for late 2014.

Back in 2011 Boeing fought with its main European competitor, Airbus, and won a $35 billion contract on aerial fueling tankers.

The U.S. Air Force expects to get its first 18 tankers by 2017 and 179 in total to be built.