The CW-21 was designed during the late 1930s. It combined light weight construction with a powerful engine, which resulted in an excellent rate of climb and manoeuvrability, allowing the fighter to quickly reach the height of attacking enemy aircraft, and attack them. The prototype was sent to China as a demonstration copy and an order for three aircraft, plus a further 32 as kits, followed. These would be assembled locally. Only the three production machines arrived in the chaos of war and would never see actual combat. A second modified variant was ordered by the Dutch government and 24 were delivered to the Netherlands Indies. The CW-21s were outnumbered and outgunned when the Japanese launched their attack on the Netherlands Indies. Despite the poor outlook, the pilots flying them put up a good fight.