Boeing Co. beat rivals Lockheed Martin Corp. and closely held Sierra Nevada Corp. in a contest valued at as much as $2.38 billion for new helicopters to guard intercontinental ballistic missile sites, the Pentagon said Monday.

As many as 84 of the Boeing MH-139 helicopters will replace decades-old UH-1 Hueys protecting nuclear bases in Montana, Wyoming and North Dakota. Delivery of the first operational helicopter is expected in fiscal 2021.

Chicago-based Boeing received a $375 million fixed-price contract for the first four aircraft. The full value of the contract would be reached if options are exercised for 80 more helicopters by September 2031 as well as sustainment, training devices and associated support equipment.

The Government Accountability Office in May rejected a protest filed by Lockheed’s Sikorsky Aircraft Corp. against terms of the Air Force’s request for proposals to build the new class of helicopters.

“Strong competition drove down costs for the program, resulting in $1.7 billion in savings to the taxpayer,” Air Force Secretary Heather Wilson said in a statement. The service’s original cost estimate was $4.1 billion.