SYDNEY — In a $11.6 billion deal, Australia is ordering 58 more F-35 fighters built by Lockheed Martin, increasing the total fleet to 72, Prime Minister Tony Abbott said Wednesday.The purchase was described by Abbott as one of Australias largest military purchases and is regionally significant for Lockheed Martin.The fifth-generation F-35 is the most advanced fighter in production anywhere in the world and will make a vital contribution to our national security, Abbott said at a news media briefing in Canberra, Australias capital.Australia ordered 14 F-35 jet fighters in 2009, and the new jets will form three operational squadrons and one training squadron, Abbott said. The first aircraft are set to arrive in Australia in 2018, entering service in the Royal Australian Air Force in 2020.The plane is part of the F-35 joint strike fighter program, the most expensive in the Pentagons history. The program, however, has been plagued by cost overruns, delays and technological flaws. Pentagon officials said that Lockheed has made progress on reining in costs in the past year.The F-35 jet fighter was conceived as a state-of-the-art aircraft that could be adapted to three branches of the military, with advances that would easily overcome the defenses of most foes. The radar-evading jets would not only dodge sophisticated antiaircraft missiles, but they would give pilots a better picture of enemy threats while enabling allies like Australia to fight more closely with U.S. forces.The U.S. armed forces are expected to buy 2,443 F-35s and nine other countries Canada, Denmark, Israel, Italy, the Netherlands, Norway, Japan, South Korea and Turkey have ordered about 700 F-35s. The plane is being built at Lockheeds sprawling aerospace complex in west Fort Worth that employs 12,500. The 100th F-35 rolled off the production line in December, and Lockheed expects to build 35 this year, up from 13 in 2011.Production is expected to ramp up in coming years as the Pentagon boosts its orders. But automatic federal budget cuts, known as sequestration, threaten to trim 17 out of a planned 343 planes the U.S. military plans to buy between fiscal 2016 and 2019. The Australian contract is not a make or break contract for Lockheed Martin, said Andrew Davies, a military analyst at the Australian Strategic Policy Institute. But it will maintain Australias already very strong air combat capability. It puts Australia in the first rank of Southeast Asian countries.The F-35 will replace 71 older F/A-18 aircraft, which will be withdrawn from service by 2022.David Johnston, Australias defense minister, said that Australian industry would benefit from a potential $1.3 billion in contracts, with domestic high-technology companies doing work on the complex aircraft.Air combat capability, he said, is the cornerstone of our national security. The report includes material from the Star-Telegram archives.