Fokker D.XXI

The Fokker D.XXI fighter was designed in 1935 for use by the Royal Netherlands East Indies Army Air Force (Militaire Luchtvaart van het Koninklijk Nederlands-Indisch Leger, ML-KNIL). As such, it was designed as a cheap and small, but rugged aircraft, which had respectable performance for its time. Entering operational use in the early years of World War II, it provided yeoman service for both the Luchtvaartafdeling (Dutch Army Aviation Group) and the Finnish Air Force, and a few were built by the Carmoli factory before the factory fell into Nationalist hands during the Spanish Civil War.

Design and development
The Fokker D.XXI was a low-wing monoplane with a fixed spatted undercarriage. Following standard Fokker design practice of the period, it had a steel tube fuselage covered in large part by fabric, with wooden cantilever wings. Power was provided by a Bristol Mercury radial driving a three-blade two-pitch propeller. When it entered service in 1938 it was a significant leap forward for the Dutch Army Aviation Group, whose fighter force had until that time consisted of aging biplanes with open cockpits. The new Fokker proved to be an extremely sturdy aircraft capable of attaining a speed of 700 km/h in a dive.

Operational history
In 1936 a few Fokker D.XXIs were used by the Spanish Republic. Although the order by the ML-KNIL was cancelled, the Luchtvaartafdeling (Dutch Army Air Force before World War II) placed an order of 36 aircraft, which were all delivered in time to participate in the war against the Germans in May 1940. The Fokker D.XXI, although much slower and more lightly armed than the Bf 109, performed surprisingly well in dogfights, due to its maneuverability. It was also one of the few aircraft that could follow a Stuka bomber into its dive. Nonetheless, the numerical inferiority of the Luchtvaartafdeling compared to the Luftwaffe resulted in the destruction of most Dutch Fokker D.XXI fighters during the campaign. Some were captured during and after 15 May, but their fates, apart from their capture, are unknown.

The Fokker D.XXI performed better and for much longer in the Finnish Air Force, which had acquired a number of licence-built fighters prior to the start of the Winter War. Against the aircraft of the Soviet Air Force, the Fokker was more evenly matched, and its rugged design with a radial engine and fixed undercarriage made it very suitable for Finnish conditions. Later in the war, as newer models of Soviet fighters appeared, the Fokker D.XXI was underpowered and too lightly armed (with only four 7.92 mm/.312 in machine guns) to compete. Plans to arm the Fokkers with 20 mm cannons were dropped and only one fighter was armed as such (two 20 mm cannons and two 7.92 mm/.312 in machine guns). Another fighter was equipped with retractable landing gear, but due to less than anticipated performance improvement, wasn't continued in the series. During the Continuation War (1941–44) the Finnish State Aircraft Factory (Valtion Lentokonetehdas, VL) also built some 50 D.XXIs with the Swedish-built Pratt & Whitney R-1535 Twin Wasp Junior as the Bristol Mercury was in short supply. These can be identified by their longer cockpit glazing, smooth cowl, and large ventral air intake under the cowl. The fixed undercarriage lent itself to both unimproved runways and conversion to skis for winter use, both of which were advantages in the Finnish theater.

Several Finnish Air Force pilots became fighter aces with the Fokker D.XXI. The top scoring Fokker ace was Jorma Sarvanto who obtained 12 5/6 victories with the type. Many other future aces scored at least one victory with the Fokker. The highest scoring airframe was FK-110, with 10 victories. This aircraft survived the war and is on display at the Central Finland Aviation Museum.

Variants

 * D.XXI: Prototype serial no FD-322
 * D.XXI-1: Pattern aircraft supplied to Denmark, 2 built powered by 645 hp Bristol Mercury VIS engines. Armed with 2x 8 mm machine guns and 2x 20 mm Madsen cannon
 * D.XXI-1:Production aircraft built at the Royal Army Aircraft Factory, 10 built powered by 830 hp Bristol Mercury VIII engines.
 * D.XXI-2: 53 Built, of which 36 were delivered to the RNLAF.
 * D.XXI-3: Finnish license-built D.XXI-2s. Number built: 38
 * D.XXI-4: Upgraded D.XXI-3, powered by 825 hp Pratt & Whitney R-1535-SB4C-G Twin Wasp Junior engines. Number built: 50
 * D.XXI-5: Upgraded D.XXI-4, powered by 920 hp Bristol Pegasus radial engines. Number built: 5
 * Project 150: Proposed version powered by a Bristol Hercules radial piston engine. Not built.
 * Project 151: Proposed version powered by a Rolls-Royce Merlin piston engine. Not built.
 * Project 152: Proposed version powered by a Daimler-Benz DB 600H engine. Not built.

Operators
1 Luchtvaartregiment (1 aviation regiment) 1 and 2 Jachtvliegersafdeling (JaVa) ''(fighter squadron) 2 Luchtvaartregiment
 * Hærens Flyvertropper (Danish Army Air Corps) received 2 aircraft and built 10 on license. Locally designated IIIJ ("third fighter aircraft")
 * Jydske Flyverafdeling - 2. Eskadrille
 * Jydske Flyverafdeling - 2. Eskadrille
 * Finnish Air Force received 7 aircraft and built 93 on license.
 * No. 10 Squadron, Finnish Air Force
 * No. 12 Squadron, Finnish Air Force
 * No. 14 Squadron, Finnish Air Force
 * No. 24 Squadron, Finnish Air Force
 * No. 26 Squadron, Finnish Air Force
 * No. 30 Squadron, Finnish Air Force
 * No. 32 Squadron, Finnish Air Force
 * 🇩🇪 Germany
 * Luftwaffe operated an unknown number of captured Dutch aircraft.
 * Dutch Army Aviation Group received 36 aircraft.
 * Dutch Army Aviation Group received 36 aircraft.
 * 🇪🇸 Spanish Republic
 * Spanish Republican Air Force May have completed 1 aircraft.

Museums

 * Aviation Museum of Central Finland has FR-110 on display having been restored with additional parts from FR-81 and FR-137.
 * Militaire Luchtvaart Museum has a replica painted in KLu markings.

Popular culture
A converted North American Harvard trainer masqueraded as a Fokker D.XXI for the Paul Verhoeven movie Soldier of Orange (1977).