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Fokker D.XXI

Fokker · Fixed Wing / Fighter · Netherlands · Interwar (1919–1938)

Fokker D.XXI — Fixed Wing / Fighter
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The Fokker D.XXI was a Dutch single-engine, single-seat fixed-gear fighter monoplane developed by Fokker in 1935 for the Netherlands East Indies and later adopted by the Royal Netherlands Air Force (Luchtvaartafdeeling) and several export operators. A parasol-cabane high-wing layout with a fabric-covered welded steel-tube fuselage and fixed spatted main gear made the design conservative even at its first flight on 27 March 1936 — but it was cheap, robust, and easy to operate from rough fields, which is what Dutch and Finnish defence staffs wanted. 147 D.XXI airframes were built: 38 by Fokker for the Netherlands, 55 by Valtion lentokonetehdas (VL/Valmet) in Finland under licence, and small batches by CASA in Spain and CKD in Czechoslovakia. It is the only Dutch combat fighter to have scored confirmed kills against the Luftwaffe.

On the morning of 10 May 1940, 28 of the Royal Netherlands Air Force's 36 D.XXIs were flyable. Across five days of fighting against overwhelming numbers, Dutch D.XXIs claimed roughly 25 confirmed and probable Luftwaffe kills — Heinkel He 111 bombers, Junkers Ju 52 transports (devastating during Luftwaffe attempts to seize The Hague airfields by airborne assault), and several Messerschmitt Bf 109s and Bf 110s — at the cost of about 70% of the fleet. Dutch ace Lt. Govert Steen scored multiple kills before being shot down. By 14 May 1940 the surviving D.XXIs had been destroyed on the ground or burned to deny capture, and the Battle of the Netherlands was over.

Finland's service record was longer and more dramatic. The Ilmavoimat operated the D.XXI through both the Winter War (1939–1940) against the Soviet Union and the Continuation War (1941–1944). Powered by Bristol Mercury VIII radials in early variants and Pratt & Whitney R-1535 Twin Wasp Juniors in later batches, Finnish D.XXIs achieved a kill ratio of roughly 16:1 against Soviet I-15bis, I-153, I-16 and SB bombers in the Winter War — the highest of any Finnish fighter type in that conflict. The aircraft was outclassed by 1942 Soviet types but soldiered on as a fighter-trainer and reconnaissance aircraft until 1948. The D.XXI's Finnish reputation as a Winter War workhorse overshadows its short, brutal Dutch service.

Dimensions are 8.2 m long with an 11.0 m wingspan; empty weight 1,450 kg, MTOW 2,050 kg. Bristol Mercury-powered variants made 460 km/h (286 mph) at altitude with a service ceiling of 11,000 m (36,000 ft). Armament was four 7.92 mm FN-Browning machine guns — two in the upper cowling, two in the wing leading edges — with some Finnish variants substituting heavier 12.7 mm Colt-Brownings. By 1940 fighter-performance standards the D.XXI was outdated against the Bf 109E, but it was a great deal better than nothing and Dutch and Finnish pilots made it count.

For Kids — a shorter, friendlier version

The Fokker D-XXI is a Dutch monoplane fighter from the 1930s. It first flew in 1936 and was the main fighter of the Royal Netherlands Air Force during the German invasion in May 1940. The D-XXI also flew with Finland, Norway, and Denmark.

The D-XXI has a Bristol Mercury VIII engine making 830 horsepower. Top speed is 286 mph, faster than most cars on a highway. The plane is small: 27 feet long with a 36-foot wingspan, about the length of a school bus. It carries four machine guns plus light bombs under the wings.

The plane has fixed landing gear, which means the wheels stay down all the time. Most fighters of 1940 had retractable gear that folded up for lower drag. The D-XXI's fixed gear made it slower than newer designs, but also simpler and cheaper to build for small countries.

About 162 D-XXIs were built. Finnish D-XXIs fought against Soviet planes in the Winter War of 1939-1940 and Continuation War of 1941-1944, claiming over 120 air victories. The Dutch D-XXIs fought hard against the German invasion in May 1940 but were quickly outnumbered. None survive today, though one is being rebuilt from parts.

Fun Facts

  • Finnish D-XXIs claimed over 120 victories against Soviet aircraft in two wars.
  • Top speed is 286 mph, faster than most cars on a highway.
  • The D-XXI has fixed landing gear, with wheels down all the time.
  • About 162 D-XXIs were built in the Netherlands, Finland, and Denmark.
  • Dutch D-XXIs flew against the German invasion in May 1940.
  • Finland used D-XXIs in the Winter War of 1939-1940 against the Soviet Union.
  • No original D-XXIs survive today; one is being rebuilt from parts.

Kids’ Questions

Why fixed landing gear?

Fixed gear is simpler than retractable gear. There are fewer moving parts, less to break, less weight, and lower cost. The trade-off is that wheels hanging down create wind drag, making the plane slower. Small countries with limited budgets often chose fixed gear in the 1930s to save money. By 1940, fixed gear was already old technology.

How did it do in WWII?

Dutch D-XXIs fought hard during the German invasion in May 1940 but were outnumbered and quickly defeated. Finnish D-XXIs did much better, claiming over 120 Soviet planes in the Winter War and Continuation War. The plane was faster and more agile than Soviet I-15 and I-16 fighters of the same era.

Why did Finland fly Dutch planes?

Finland could not buy planes from major powers during the Winter War because everyone wanted to stay neutral. The Dutch were willing to sell D-XXIs to Finland. Finland also built its own D-XXIs under license. The plane was simple enough that Finnish factories could keep building them even during wartime.

Variants

D.XXI Series I (Mercury VI / VII, Dutch 1938)
Initial Dutch production batch — 36 built by Fokker with Bristol Mercury VI / VII radials. Operated by the Royal Netherlands Air Force from 1938 until destruction or capture in May 1940.
D.XXI Series II (Finnish licence, Mercury VIII)
Finnish licence-built variant. 38 produced by VL with Bristol Mercury VIII engines. Backbone of Finnish Winter War (1939-1940) air-defence.
D.XXI Series III (R-1535, Finnish)
Pratt & Whitney R-1535 Twin Wasp Junior-powered Finnish variant. 55 produced. Continuation War service 1941-1944, then trainer role until 1948.
D.XXI (Spanish, Czech licence batches)
Small CASA (Spain) and CKD (Czechoslovakia) licence batches built before WWII. Limited combat impact compared to Dutch and Finnish service.

Notable Operators

Royal Netherlands Air Force / Luchtvaartafdeeling (former)
Primary operator. 36 D.XXIs in service May 1940; 28 flyable on 10 May 1940. Fought the Battle of the Netherlands against the Luftwaffe — claimed ~25 Luftwaffe kills and disproportionately damaged the Ju 52 transport fleet during the failed German airborne assault on The Hague. All flyable D.XXIs lost or destroyed by 14 May 1940.
Finnish Air Force / Ilmavoimat (former)
Major operator. 93 D.XXIs in Finnish service 1939-1948. Heavy Winter War combat (16:1 kill ratio against Soviet I-15bis / I-153 / I-16 / SB). Continuation War 1941-1944 fighter and reconnaissance role; trainer until 1948 retirement.
Republican Spain / Czechoslovakia (former)
Limited operations. Spanish CASA-built D.XXIs saw minimal combat in the late Spanish Civil War; Czech CKD-built airframes were captured by Germany in 1939 before reaching frontline service.
Preservation / museums
No original D.XXI airframes survive intact. Replicas exist at the Militaire Luchtvaart Museum (Soesterberg, Netherlands) and the Finnish Air Force Museum (Tikkakoski, Finland). The Dutch replica was assembled from period components recovered from 1940 wreckage sites.

Frequently Asked Questions

How many Luftwaffe aircraft did D.XXIs shoot down?

Around 25 confirmed and probable kills during the five-day Battle of the Netherlands (10–14 May 1940). The most consequential were Junkers Ju 52 transports — Dutch D.XXIs intercepted German airborne assault waves on the morning of 10 May and devastated the transport fleet attempting to drop paratroops on the Ypenburg, Valkenburg, and Ockenburg airfields around The Hague. Roughly 280 Ju 52s were lost or damaged in the Netherlands campaign overall, across all causes — flak, fighters, ground combat — and D.XXIs accounted for a major share. The German airborne plan to capture the Dutch government in The Hague failed, partly because of D.XXI interception.

Why did the D.XXI succeed in Finland against the Soviets?

Several factors. (1) Soviet 1939-1940 fighters — the I-15bis biplane, I-153 biplane, and I-16 monoplane — were rough peers of the D.XXI in performance, with no decisive technology advantage on either side. (2) Finnish pilots used finger-four tactics and disciplined deflection shooting against tightly-packed Soviet bomber and fighter formations. (3) Finnish ground control was effective. (4) The D.XXI's fixed gear and Bristol Mercury tolerated extreme cold (-40 °C operations). (5) The Soviet Air Force in 1939 was still suffering the after-effects of Stalin's purges and was poorly led. By 1942 the Soviet VVS had recovered and re-equipped with LaGG-3, Yak-1, and Hurricane / P-40 lend-lease, and the D.XXI was outclassed.

Why was the D.XXI's gear fixed and not retractable?

Cost, weight, and reliability. Fokker designed the D.XXI specifically for the Netherlands East Indies budget — a colonial air force with limited maintenance infrastructure operating from rough tropical fields. Fixed spatted gear cost less to build, saved around 80 kg over a retractable system, and could not jam in the closed position over the East Indies jungle. By 1940 European standards the design was obsolete; by Finnish forest-airstrip standards it was still adequate.

How does the D.XXI compare to the Bf 109?

The Messerschmitt Bf 109E — the 1940 service variant — was superior in every measurable dimension: top speed (570 km/h vs 460 km/h), climb rate, ceiling, armament (cannon-equipped vs four rifle-calibre MGs), and pilot armour. Dutch and Finnish D.XXIs nonetheless scored kills on Bf 109s by exploiting the D.XXI's tighter turn radius (lower wing loading), surprise, and pilot skill. The mismatch spanned three generations of fighter development: the D.XXI was a 1934 design; the Bf 109 was a 1937 second-generation monoplane.

Where can I see a D.XXI?

Two replicas. (1) Militaire Luchtvaart Museum, Soesterberg (Netherlands) — full-scale replica incorporating recovered wartime components. (2) Finnish Air Force Museum, Tikkakoski (Finland) — replica representing the Finnish service variant. No original D.XXI airframes survive intact; all Dutch examples were destroyed in May 1940 and Finnish examples were scrapped after retirement.

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