Entering service with the Dutch Army's Aviation Branch from early 1938, the Fokker D.XXI was also built under license in Denmark and Finland. Dutch D.XXIs subsequently saw less than a week of action following the German invasion of western Europe on 10 May 1940, with many of the country's 28 fighters being destroyed on the ground. Those that survived the initial onslaught inflicted notable losses on the Luftwaffe.By then, however, the D.XXI had found everlasting fame in Finland during the Winter War of 1939-40. Proving itself a real thorn in the side of the Soviets, the fighter, operating in primitive conditions and against vastly superior numbers, racked up an incredible score against the Red Air Force, and in particular its bomber units.

No fewer than ten pilots became aces during this brief, but bloody, campaign, with a similar number claiming four victories and subsequently 'making ace' in later types. The D.XXI also has the distinction of producing the first 'ace in a single mission' in World War 2 when 1Lt Jorma Sarvanto shot down six Ilyushin DB-3 bombers on 6 January 1940.