The first F-35 squadron is ready for combat, according to the Marines

WASHINGTON (Reuters) - U.S. Marine Corps Commandant General Joseph Dunford has declared an initial squadron of 10 Lockheed Martin Corp F-35B fighter jets ready for combat, sources familiar with the decision said Friday.

The decision, to be announced formally later Friday, makes the Marines to first U.S. military service to declare an "initial operational capability" (IOC) of the F-35 fighter, a key milestone for the $391 billion program after years of cost overruns and schedule delays.

The F-35B model of the aircraft can take off from shorter runways and land like a helicopter.

The F-35 progam is the single most expensive military program in history. The expected lifetime cost of the program is estimated at $1.5 trillion. The cost reflects the wide range of abilities that the F-35 is meant to possess.

The aircraft comes in three varieties, each of which is specialized for a branch of the military. While the Marines have the F-35B, which can take off like a helicopter, the Air Force and Navy have the F-35A and C models respectively.

Although the F-35 is meant to ultimately replace the legacy US aircraft and function as a Jack-of-all-trades combat system, the plane has suffered from multiple shortcomings and delays to date. Aside from massive cost overruns, the aircraft suffers from a plethora of problems including software delays and flight control issues.

Most recently, a test variant of the F-35A was incapable of effectively dogfighting against an F-16 legacy jet that it was meant to replace.

(Additional reporting done by Andrea Shalal)