The Wichita Model 75 two-seater Stearman Kaydet biplane, introduced in 1934, became an unexpected success during World War II. Army trainers were PT-13, -17, 18, and 27 versions. Navy trainers carried the NS and N2S designations. Despite its almost obsolete design, its simple, rugged construction made it ideal as a trainer. Boeing built 8,584 Kaydets in all versions, plus the equivalent of 2,000 more in spare parts between 1936 and 1944. Many were still in use during the 1960s as crop dusters.