Boeing's MH-139 helicopter was selected by the U.S. Air Force to replace its aging UH-1N Huey helicopters. (Fred Troilo/Boeing)

The U.S. Air Force says it will turn to Chicago-based defense giant Boeing to replace its aging fleet of UH-1N Huey helicopters, which are used to protect the U.S. military’s ground-based ballistic missiles, in a stunning upset against its Bethesda-based rival, Lockheed Martin.

The Air Force announced Monday it has awarded Boeing’s Arlington-based defense division the first phase of a $2.38 billion contract to procure 84 of Boeing’s MH-139 helicopters, the first of which is to be delivered in 2021. Air Force Secretary Heather Wilson hailed the contract as a win for taxpayers, noting that initial estimates had pegged its total cost at $4.1 billion.

"Strong competition drove down costs for the program, resulting in $1.7 billion in savings to the taxpayer,” Wilson said in a statement.

The UH-1N replacement is seen as an important procurement because the military uses them to protect U.S.-based nuclear missile launch sites from attack and guard nuclear warheads as they are transported across the country. They would also probably be used to transport top officials out of Washington in the event of a nuclear disaster.

Like much of the U.S. nuclear infrastructure, however, the service’s Huey models are getting old. The UH-1 family of helicopters dates to the 1960s when thousands of them were deployed in Vietnam. The UH-1N first entered the Air Force’s inventory in 1970.

Loren Thompson, a defense consultant with the Lexington Institute, which is funded by defense contractors including Boeing, said the Air Force’s language in the announcement suggests it had focused closely on driving down prices rather than tacking on fancy new capabilities.

“The Air Force has become infamous among military contractors for driving bidders to the lowest possible price on major procurements,” Thompson said.

Boeing may have lowballed competing proposals from Lockheed Martin and Sierra Nevada, which had each pitched souped-up versions of the UH-60 Black Hawk.

It was the second major aircraft procurement in the past month to fall in Boeing’s favor. Just weeks earlier, the company won an $805 million contract to build the Navy’s MQ-25 aerial-refueling drone, which Lockheed had also competed for.

If Boeing is successful in its bid to build the Air Force’s next fleet of pilot training aircraft — an estimated $18 billion procurement that both companies are pursuing — it could tip the scales among the world’s two biggest defense contractors for the first time in recent memory. The Air Force has said it will announce its decision on that program by the end of September.

The Huey award is seen as a major upset for Lockheed Martin, which has become the world’s largest defense contractor and the manufacturer of the F-35 Joint Strike Fighter. Lockheed was widely expected to win the helicopter replacement, in part because the Air Force had at one point planned to pursue part of the replacement program on a sole-source basis, turning to UH-60 Black Hawks made by Lockheed Martin subsidiary Sikorsky.

Lockheed spokeswoman Sharon Parsley declined to detail the company’s next steps.

“We are disappointed in the U.S. Air Force’s decision but remain confident the HH-60U Black Hawk is the strongest, most capable solution for the UH-1N Huey Replacement Program’s critical no-fail mission of protecting our nation’s nuclear missile silos and supporting the continuity-of-government mission,” Parsley said in an email. “We remain committed to delivering superior helicopters to the Air Force in our existing and future contracts.”

The competition has already been subject to one protest, with Lockheed seeking to overturn the award before bids were even submitted. The company took issue with an Air Force requirement that valuable software licenses related to the helicopter be turned over the Air Force.

Sierra Nevada, the third bidder, could also try to overturn the bid. Asked whether it will do so, a company spokesman said: “While we are disappointed by the announcement, [Sierra Nevada] and the Sierra Force helicopter team will review the Notification Letter and we will elaborate further on future options for rotary-wing aircraft capabilities once complete.”

Correction: An earlier version of this story misidentified the type of Huey helicopters that were used most heavily in Vietnam. Thousands of UH-1 family helicopters were deployed in Vietnam, but most were UH-1D or UH-1H models.