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(Adds confirmation from Air Force, details)
By Idrees Ali and Andrea Shalal
WASHINGTON, Aug 2 (Reuters) - The U.S. Air Force on Tuesdaydeclared an initial squadron of Lockheed Martin Corp F-35A fighter jets ready for combat, marking a major milestonefor a program that has faced cost overruns and delays.
The move is another achievement for the $379 billionprogram, the Pentagon's largest weapons project. The Air Forcefollows the U.S. Marine Corps, which declared a first squadronof F-35s ready for combat in July 2015.
"The U.S. Air Force decision to make the 15 F-35As at HillAir Force Base combat ready sends a simple and powerful messageto America's friends and foes alike - the F-35 can do itsmission," F-35 program chief, Air Force Lieutenant GeneralChris Bogdan, said in a statement.
Officials say the F-35 will give the U.S. military theability to detect enemy aircraft and other threats far beyondcurrent ranges, allowing the jets to strike targets anddisappear long before they are detected.
The U.S. Air Force plans to buy a total of 1,763 F-35Aconventional takeoff and landing jets in coming years and willoperate the largest F-35 fleet in the world.
The Pentagon's F-35 program office on Monday announced thatthe F-35A had launched an AIM-9X air-to-air missile to hit and"kill" a target simulating a drone over a military test rangeoff the California coast on July 28.
"After launch, the missile successfully acquired the targetand followed an intercept flight profile before destroying thedrone, achieving the first F-35 air-to-air kill or 'BoolaBoola,' which is the traditional radio call made when a pilotshoots down a drone," the program office said.
The same F-35 pilot who hit the drone also used aninternally carried AIM-120C missile against another target dronethat was beyond visual range, telling it to self-destruct rightbefore impact, the program office said in a statement.
Lockheed is building three models of the F-35 Lightning IIfor the U.S. military and 10 countries that have already orderedthe jets: Britain, Australia, Norway, Italy, Turkey, Denmark,the Netherlands, Israel, South Korea and Japan.
"It will provide airmen unprecedented lethality andsurvivability, a capability they will use to defend America andour allies for decades to come," Lockheed Martin said in astatement.
The Pentagon's F-35 program office said it remained innegotiations with Lockheed about long-delayed contracts for thenext two batches of F-35 jets, deals worth about $15 billion.
"We're seeking a fair deal for the F-35 enterprise andindustry," said F-35 program spokesman Joe DellaVedova.
The program, first launched in 2001, has made strides inrecent years after huge cost overruns and technical problemsthat sent the project cost up by nearly 70 percent.
Earlier problems with the fighter jet included issues withthe radar software and complications which increased the risk ofneck injury to lightweight pilots when they ejected from theaircraft.
Industry and U.S. defense officials say they are workinghard to continue driving down the cost of the new warplanes toaround $85 million per plane by 2019, as well as the cost ofoperating the jets.
"The program is not doing everything they wanted it to do...But they're at a point now where it is stabilizing and so it isprogress," said Todd Harrison, a defense analyst at the Centerfor Strategic and International Studies. (Reporting by Andrea Shalal and Idrees Ali. Additionalreporting by David Alexander.; Editing by Marguerita Choy andAndrew Hay)