Frederick Koolhoven, also called Frits and known to his friends as Cully, built first aircraft 1910 and then designed for British Deperdussin, Armstrong Whitworth and British Aerial Transport (BAT), latter company’s aircraft having designations numbered FK.22 - FK.28. After Armistice he returned to native land and became designer for NVI (Nationale Vliegtuigindustrie) at The Hague. In 1926 he set himself up as a freelance consultant at The Hague, and in 1934 he formed N.V. Koolhoven Vliegtuigen as a limited company with offices and factory at Waalhaven aerodrome, Rotterdam. This was destroyed by bombing 10 May 1940. Major types included FK.29 cabin biplane with engine on hinged nose, FK.31 parasol recon-fighter, FK.41 and 43 cabin monoplanes, FK.46 biplane trainer, FK.49 and 50 high-wing transports, FK.51 basic trainer, FK.52 2-seat fighter, FK.55 experimental fighter, FK.56 basic trainer and FK.58 fighter used by Polish forces in France 1940.