WASHINGTON — The U.S. Air Force has awarded Sikorsky Aircraft a $1.28 billion contract to develop a new combat rescue helicopter based on the company's workhorse UH-60 Black Hawk, the Pentagon said Thursday.

The contract covers development and delivery of four new Combat Rescue Helicopters, capping more than a decade of repeated unsuccessful efforts by the Air Force to replace its aging fleet of HH-60G Pave Hawk helicopters.

It marks the start of a major acquisition program for 112 helicopters that will be worth up to about $7.9 billion to Sikorsky over the long term, the Pentagon and Sikorsky said in separate statements.

The Air Force said that the contract was structured to allow fluctuating quantities, and that the deal came in about $700 million below its affordability target.

Sikorsky, a unit of United Technologies Corp., welcomed the deal, noting that it has built combat search-and-rescue helicopters for the U.S. military since 1943. Sikorsky President Mick Maurer said that the helicopters allowed the Air Force to "perform one of its most important and sacred missions — bringing our downed service members home safely."

"We are honored that the Air Force has selected Sikorsky to develop and build the new Combat Rescue Helicopter," Maurer said in a statement.

A spokeswoman for the company said that the final assembly location for the helicopter had not been decided, but that crucial components would be built and substantial design work done in Stratford, where Sikorsky is based.

U.S. Sens. Richard Blumenthal and Chris Murphy, Democrats from Connecticut, said in a joint statement: "Sikorsky-made helicopters are second to none, and this contract will be a win-win for both taxpayers and our brave servicemen and women who rely on these helicopters both in combat and disaster relief operations."

Blumenthal said that getting the contract was not done easily.

"It was a huge and historic fight," Blumenthal said. Most of the difficulties, he said, came "because we had to work against resistance from the Air Force, which seemed to prefer to use the decades-old helicopters that are inadequate."

Air Force Secretary Deborah James said that the Air Force was the primary service responsible for global personnel recovery operations, and remained committed to a mission that she called "part of the military ethos."

More than 12,200 U.S., allied and host nation forces have been saved in rescue missions around the world, the Air Force said.

The Air Force announcement comes after one of the longest-running and controversial acquisition programs that the service has attempted in recent decades.

The Air Force awarded Boeing Co. a contract to build 141 rescue helicopters based on its twin-rotor CH-47 "Chinook" design in 2006, but the deal was protested immediately by the losing bidders — Lockheed Martin Corp. and Sikorsky — and later canceled by then-Defense Secretary Robert Gates.

In 2012, the Air Force received approval to restart the program, but Boeing, Northrop Grumman Corp. and Europe's Airbus later dropped out of the competition, arguing that the Air Force had skewed the requirements to favor Sikorsky's helicopter.

In March, the Air Force's 2015 budget request to Congress omitted funding for the program, but officials added the program back in the same day under pressure from senior U.S. lawmakers.