The makers of two of the U.S. military's most important combat aircraft are joining forces.

Defense giant Lockheed Martin, prime contractor of the F-35 Joint Strike Fighter program, announced Monday that it will buy Sikorsky Aircraft from United Technologies Corp. for an announced price of $9 billion. The companies said, however, that the actual price would be $7.1 billion at closing in late 2015 or early 2016 once tax advantages from the deal were taken into account.

Sikorsky makes the multi-service and multi-national H-60 Hawk line of helicopters, meaning the combined company will have a major share of the Pentagon's business for military aircraft over the next decades.

The F-35 is expected to replace most combat aircraft for the Air Force, Navy and Marine Corps starting this year, and the Hawk is used by all the armed services — Black Hawk for the Army, Sea Hawk for the Navy and Pave Hawk for the Air Force.

"Sikorsky is a natural fit for Lockheed Martin and complements our broad portfolio of world-class aerospace and defense products and technologies," Lockheed Martin CEO Marillyn Hewson said in a statement announcing the deal. "I'm confident this acquisition will help us extend our core business into the growing areas of helicopter production and sustainment."

United Technologies CEO Gregory Hayes said the sale would allow his company to focus more on providing high-technology systems and services to the aerospace and building industries, and better position Sikorsky as a leader in its field. United Technologies also owns aircraft engine-maker Pratt & Whitney.

"Sikorsky's acquisition by Lockheed Martin, one of the world's leading aerospace and defense companies, will ensure it remains a technology leader at the forefront of vertical lift," Hayes said.