The reveal of a fourth prototype three and half years after the first J-20 flight in January 2011 compares favorably with many other "fifth generation" fighter programs: the time between the first (September 1997) and fourth (October 1997) F-22 Raptors was two years, and for the PAK-FA, close to three years between the first (January 2010) and fourth (December 2012). As with so much of the program, the difference between the debut launches of the F-35 is a bit more complicated. While the first prototype F-35 (F-35A "AA-1") flew in December 2006, the fourth overall F-35, the F-35A "AF-1" first flew in late 2009, nearly three years later. But the fourth example of the F-35A variant, AF-3, only flew in July 2010, making that a gap of nearly four years. For the F-35B variant, the first prototype "BF-1" flew in June 2008, while the fourth "BF-4" flew in April 2010, almost two years apart.