United States had retired the F-111 (it "was nine percent of Tactical Air Command's fleet but ate up a whopping 25 percent of the maintenance budget", USAF pilot Richard Crandall said) so Australia was the only operator. By 2009 the remaining 18 aircraft reportedly required the most maintenance of any warplane in the world, an average of 180 hours for every flight hour compared to 30 hours for the F-22 Raptor. In March 2008, after a review, the new Labor government confirmed the previous Howard Government's decision to the purchase of 24 F/A-18F Super Hornets until the delivery of the F-35; in 2010, the government signed the acquisition contract. The final RAAF F-111 aircrew conversion took place in 2009, with four pilots and two Air Combat Officers (ACOs) qualifying. The RAAF retired its last F-111s on 3 December 2010, after the final flight by aircraft from No. 6 Squadron over southern Queensland. Australia is currently a partner in the development of the Lockheed Martin F-35 Lightning II stealth fighter, with plans for the country to procure up to 100 examples to replace the F-111 as well as the F/A-18 Hornet. Between 21 and 24 November 2011, 23 of the RAAF's F-111C and F-111Gs which had not been selected for preservation were buried at the Swanbank landfill site outside of Ipswich, Queensland. The RAAF had considered scrapping these aircraft, but concluded that it would be cheaper to bury them as they also contained asbestos in the airframes. The remaining ex-RAAF F-111s will be placed on display. Variants F-111C The F-111C was the export version for Australia, combining the F-111A design with the longer F-111B wings and the strengthened FB-111A undercarriage. RF-111C Four F-111C aircraft were modified to RF-111C reconnaissance configuration. These aircraft met the RAAF's requirement for aircraft to reinstate its photographic reconnaissance capacity. While the original order for F-111s specified that 18 would be strike variants and six reconnaissance variants, the RAAF later agreed to accept all 24 as strike aircraft and later retrofit six with reconnaissance pallets. In 1971 the USAF dropped plans to fit some of its F-111s as reconnaissance aircraft, but sold the design of the reconnaissance pallet to Australia for $3 million. At this time the RAAF decided to fit the pallet to four rather than six aircraft. The reconnaissance pallet contains four cameras and an infrared linescanner unit and is fitted in the F-111's weapons