Singapore has shown “tremendous interest" in Lockheed Martin's F-35 Joint Strike Fighter and will likely decide by summer whether to buy the warplane, the Pentagon's F-35 program chief said Wednesday. Air Force Lieutenant General Christopher Bogdan told a Senate Armed Services subcommittee that he expects Singapore to decide by summer whether to join the multinational fighter plane program. Bogdan said that he is also cautiously optimistic that South Korea could decide to buy the radar-evading F-35 in its 60-fighter competition, with a decision expected there in June.