WASHINGTON — Boeing declined to bid on the U.S. Air Force’s Ground Based Strategic Deterrent program by the deadline of Dec. 13, leaving Northrop Grumman as the de facto winner of the contract.

At play is an $85 billion award to design the Air Force’s next-generation intercontinental ballistic missiles, which will replace the Minuteman III. Northrop and Boeing each were awarded contracts in 2017 for the technology-maturation and risk-reduction phase of the program — meaning Boeing’s departure leaves the Air Force with only Northrop as an active bidder.

“Boeing is disappointed we were unable to submit a bid to the GBSD solicitation,” the company wrote in a statement. “We have been proud and honored to contribute to the ICBM mission for more than 60 years. Boeing continues to support a change in acquisition strategy that would bring the best of industry to this national priority and demonstrate value for the American taxpayer.”

In a statement, the Air Force confirmed that it had received only one proposal. A spokesman for Northrop Grumman confirmed the company had bid on the competition.

“To date, the competitive Technology Maturation and Risk Reduction phase has provided the DoD with an unprecedented amount of technical and cost knowledge,” wrote Air Force spokeswoman Capt. Cara Bousie in a statement. “The Air Force will proceed with an aggressive and effective sole-source negotiation. We remain on track for a contract award in the fourth quarter of Fiscal Year 2020.”

Boeing’s no-bid on the competition was not surprising. The company announced in July that it would not bid on GBSD unless the Air Force made changes to its acquisition strategy. Specifically, Boeing claimed that Northrop’s purchase of one of the only two U.S. solid-fuel rocket motor manufacturers — Orbital ATK, now known as Northrop Grumman Innovation Systems — gave the company an unfair advantage in terms of being able to offer the lowest-cost system.

It called on the Air Force to level the playing field. “We lack confidence in the fairness of any procurement that does not correct this basic imbalance between competitors,” Boeing Defense and Security head Leanne Caret stated in a July 23 letter, adding that the current acquisition strategy gave Northrop “inherently unfair cost, resource and integration advantages.”

Boeing then pushed the Air Force to mandate a joint bid with Northrop. Ultimately, the Air Force declined to intervene, and Northrop chose its own industry team, which did not include Boeing as a supplier.

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Then, in October, the Air Force stopped funding Boeing’s technology maturation and risk reduciton contract.

During a news conference at the Dubai Airshow in November, Caret told reporters she was still hopeful the Air Force would modify its acquisition plan, though she acknowledged that the service showed no signs of doing so.