Defense (DOD) intended to acquire 31 F/A-18s in FY2010. Congress requested the DoD study a further multi-year contract so that a projected fighter shortfall could be averted; in 2006, the Navy was 60 fighters below its validated requirement. The FY2010 budget bill authorized a multiyear purchase agreement for additional Super Hornets. A multi-year contract was finalized on 28 September 2010, reported as saving $600 million over individual yearly contracts, for 66 Super Hornets and 58 Growlers to mitigate a four-year delay in the F-35 program. On 7 August 2014, U.S. defense officials announced they had been authorized to launch bombing missions upon Islamic State (IS) forces in northern Iraq. The decision to take direct action was made to protect U.S. personnel in the city of Irbil and to ensure the safety of transport aircraft making airdrops to Yazidi civilians. Early on 8 August, two Super Hornets took off from and dropped 500 lb laser-guided bombs on a "mobile artillery piece" the militants had been using to shell Kurdish forces defending the city. Later that day, four more aircraft struck a seven-vehicle convoy and a mortar position. On 18 June 2017, a U.S. Navy F/A-18E shot down a Syrian Air Force Su-22 fighter-bomber that allegedly had bombed a position held by U.S.-supported Syrian Democratic Forces (SDF) near Tabqa; the Syrian government claimed the Su-22 was bombing an IS position. This was the first aerial kill of a manned aircraft by an American fighter since 1999, the first by the Navy since the 1991 Persian Gulf War, the first kill by a Super Hornet, and the third kill by an F/A-18. An E-3 Sentry issued several warnings to the Su-22 and, after it dropped bombs near SDF fighters, the F/A-18E, piloted by Lieutenant Commander Michael "MOB" Tremel, a pilot assigned to Strike Fighter Squadron 87 aboard the carrier George H.W. Bush, independently chose to shoot it down based on established rules of engagement. The F/A-18E first missed with an AIM-9X Sidewinder, then hit the Su-22 with an AIM-120 AMRAAM; the encounter lasted eight minutes. In 2018, Boeing was awarded a contract to convert nine single-seat F/A-18E Super Hornets and two F/A-18F two-seaters for Blue Angels use; these are to be completed by 2021. Royal Australian Air Force On 3 May 2007, the Australian Government signed an A$2.9 billion contract to acquire 24 F/A-18Fs as an interim replacement for the Royal Australian Air