WASHINGTON — The U.S. Air Force is close to deciding on its replacement for its aging fleet of UH-1N Iroquois helicopters, which are currently tasked with security missions as well as protecting America's nuclear missile arsenal.

Manufactured by Bell, UH-1N, the helicopter affectionately called "Huey," first entered service in 1970 to assist in search and rescue missions. Since then, the Air Force has expanded the Huey's role to include flying above nuclear missile silos and VIP transportation.

The Air Force has been eyeing a replacement for the aging UH-1N fleet for more than a decade. The first manifestation of the service's ambition to procure new helicopters came in December 2016 when the Air Force issued its initial request for proposal.

America's top nuclear commander complained that the procurement process for the new helicopters responsible for securing the sites of America's nuclear missile silos was "taking way too long."

"We are going to get a new helicopter in the missile fields," Air Force Gen. John Hyten said earlier this year during his opening remarks at the 2018 STRATCOM Deterrence Symposium in Omaha, Nebraska. "We are going to get a new helicopter if I have to die trying or if I have to kill somebody to do it."

"It is taking way too long," Hyten said.

The long-awaited Pentagon contract is expected to be awarded by the end of the month with deliveries starting as early as 2020.

Three defense companies are in the running for the lucrative Pentagon contract for 84 aircraft: Sierra Nevada Corp., Boeing partnered with Leonardo, and Sikorsky, a unit of Lockheed Martin.

Both Sierra Nevada and Sikorsky are offering derivatives of the Black Hawk medium lift-utility helicopter and Boeing alongside Leonardo is pitching the MH-139, a militarized version of Leonardo's AW139 commercial aircraft.

"The MH-139 is is an aircraft that the Air Force doesn't have to go and pay to develop because it's already flying," Rick Lemaster, Director of Global Sales and Marketing for Boeing's Vertical Lift and Military Aircraft programs, told CNBC. He added that more than 250 governments already use the civilian version of the helicopter.

"The life cycle of the aircraft is notionally a 30-year life cycle and will be able to save the Air Force about a billion dollars in terms of buying and operating over that time frame. That's real money," he added.