WASHINGTON —The U.S. Air Force has selected Boeing to replace the service's aging fleet of UH-1N Iroquois helicopters, which are currently tasked with security missions as well as protecting America's nuclear missile arsenal.

The long-awaited Pentagon contract is worth $2.4 billion for up to 84 aircraft. The service awarded Boeing approximately $375 million for the first four helicopters on Monday.

"Strong competition drove down costs for the program, resulting in $1.7 billion in savings to the taxpayer," Secretary of the Air Force Heather Wilson said in a statement.

Three defense companies were in the running for the lucrative Pentagon contract: Sierra Nevada Corp., Boeing partnered with Leonardo, and Sikorsky, a unit of Lockheed Martin.