F designation is expected, but the series number 35 comes from its X-35 designation, rather than the next available F- series number (24). FB-111 Aardvark Should have been designated BF-111 as a fighter modified for bombing capabilities. Also should have used the next available number in the bomber sequence but 111 was retained for commonality with the F-111 from the pre-1962 system. F-117 Nighthawk Designated as part of series continuing from the pre-1962 system and latterly used to identify foreign aircraft acquired by the government, e.g., YF-113 was a MiG-23. Additionally, the basic mission designation as fighter implies air-to-air capabilities though the F-117 does not possess any. There have been conjecture and anecdotal reports concerning purported air-to-air capabilities targeted toward destroying Soviet AWACS craft. SR-71 The SR-71 designator is a continuation of the pre-1962 bomber series, which ended with the XB-70 Valkyrie. During the later period of its testing, the B-70 was proposed for the Reconnaissance/Strike role, with an RS-70 designation. The USAF decided instead to pursue the Lockheed A-12 which was dubbed RS-71 (Reconnaissance/Surveillance; unrelated to the S mission designation for anti-submarine warfare). Then-USAF Chief of Staff Curtis LeMay preferred the SR (Strategic Reconnaissance) moniker and wanted the reconnaissance aircraft to be named SR-71. Before the Blackbird was to be announced by President Johnson on 29 February 1964, LeMay lobbied to modify Johnson's speech to read SR-71 instead of RS-71. The media transcript given to the press at the time still had the earlier RS-71 designation in places, creating the myth that the president had misread the aircraft's designation. TR-1 A variant of the U-2; uses its own modified mission letter (T for Tactical) with basic mission letter (R for Reconnaissance). The U-2 was initially designated as "utility" to obfuscate its reconnaissance capabilities. Following shootdowns of the aircraft, this subterfuge was pointless. The TR-1, first flown in 1981, was later re-designated U-2R in 1991 after the end of the Cold War for uniformity. KC-45 Proposed tanker based on the Airbus A330 for the KC-X program. This designation skipped 42–44. KC-767 Skipped hundreds of C- series numbers to use Boeing's model number. Has conformant basic mission and modified mission letters. Only used for aircraft sold to foreign air forces. The U.S. Air Force ordered the Boeing 767-based tanker KC-46. Skipped design numbers The design number "13" has been skipped in many mission and vehicle series for its association with superstition.