WASHINGTON — The first two production MH-139A Grey Wolf helicopter are now in final assembly and Boeing said it expects the long-awaited delivery of the first of these helicopters to the Air Force in mid-2024.

The sixth and final test Grey Wolf helicopter was delivered in October, the company said in a statement Monday, marking the end of its research, development, test and evaluation phase and a move to toward solely concentrating on production.

The Grey Wolf is slated to replace the Air Force’s fleet of 63 Vietnam-era UH-1N Huey helicopters for security personnel to patrol the service’s nuclear missile fields and to transport senior officials in the Washington area. The Air Force plans to buy as many as 80 MH-139s, which are a militarized version of Italian aerospace firm Leonardo’s AW139 commercial helicopter design.

“Delivering all of the RDT&E aircraft to the Air Force enables them to continue critical operational testing and allows Boeing to focus on building the first production aircraft,” Azeem Khan, Boeing’s MH-139 program director, said in the statement. “The Grey Wolf will provide crucial national security capability improvements to the Air Force. This is an important step in getting the aircraft into service.”

The Air Force in March reached a Milestone C decision to move forward on low-rate initial production of the Grey Wolf, and awarded Boeing and Leonardo a $285 million contract to start building the first 13 helicopters.

Leonardo starts building the MH-139A at its factory in Philadelphia and then moves it to Boeing’s Ridley Park, Pennsylvania, facility where it is adapted for military use.

Boeing spokesman Brett Anker told Defense News the first two production MH-139 in final assembly are still at Leonado’s facility, as the companies ramp up work on their initial 13 helicopters. Anker said procurement and manufacturing work is already under way.

The MH-139 program has struggled in recent years with unexpected challenges integrating military systems on to the commercial helicopter platform, which caused delays that led to a schedule breach in April 2021, the Government Accountability Office said in a weapons systems assessment report this year.

The MH-139 program also experienced delays getting necessary FAA certifications, which in 2021 caused the Air Force to push procurement plans back. Program officials told GAO that the FAA certifications came in 2022, and allowed the service to accept the first four test helicopters.

The milestone decision beginning production ultimately came about a year and a half later than expected due to the FAA certification testing delays, GAO said.