Ahead of the publication of his latest release Holland 1940, Ryan K. Noppen gives us insight into the Dutch Airforce and the drive for its modernisation at the eve of the Second World War. Full of amazing artwork, read more to learn about the aircrafts selected to expand the Air Service of the Royal Dutch Army. 

Holland 1940 publishes on Sep 16. Click here to find out more and pre-order your copy. 

The Dutch Air Force Which Could Have Been and the High-Performance Interceptor Which Never Was…

Most histories of World War II barely mention the Netherlands Campaign of May 1940, simply stating that the Netherlands was overrun by German forces in five days. While Dutch forces were compelled to surrender after five days of fierce combat, the brief mention of the five-day-overrun belies the impact the campaign had upon the German Luftwaffe in particular – the subject of my new book Holland 1940: The Luftwaffe's First Setback in the West. When hundreds of Luftwaffe aircraft roared over the Netherlands on the morning of May 10, 1940, an outnumbered and in some ways outmoded Dutch air force conducted a spirited defense which led to a series of tactical failures for the Luftwaffe over the course of the five-day campaign. It should be noted that Dutch skies were defended by an air arm which was only a fraction of a pre-war plan to create a modern and balanced air defense force. This article examines Dutch efforts to acquire a modern, high-performance interceptor on the eve of World War II and highlights the Dutch understanding of the role that modern air defense would play in any act of aggression against the Netherlands.

By the early 1930s, the Luchtvaartafdeeling der Koninklijke Landmacht (LVA), or Air Service of the Royal Dutch Army, was largely a token force, composed of a single Jachtvliegtuigafdeeling (JaVA), or fighter squadron, made up of Fokker D.XVI and D.XVII biplane fighters, two army-cooperation groups consisting of Fokker C.V multipurpose biplanes, and a training squadron possessing three Fokker F.VIIa/3m transport/bombers and other trainers. The LVA had only one permanent ground installation and airfield at Soesterberg, just east of Utrecht, at which these units were based. The rise of Hitler in Germany and the failure of the League of Nations to effectively counter Japanese, Italian, and later German military aggression created new defense concerns which the small LVA was unsuited to face. Luitenant-kolonel Petrus Wilhelmus Best, who was appointed commander of the LVA on November 1, 1933, immediately recognized his service’s shortcomings against the rising tide of militarism and rearmament sweeping across the Continent in the mid-1930s. In large part due to Best’s lobbying, the Inspectie der Militaire Luchtvaart (Military Aviation Inspectorate) or IML was formed in April 1935 under the leadership of Generaal-majoor Marius Raaijmakers. The IML sought to remedy the poor operational status of the LVA, create a modern aircraft procurement program, and construct new airfields in order to effectively disperse and service its aircraft. In early 1937, the IML published its four-year-plan to expand the LVA to a size necessary to meet the new objectives, given the advances in technology and change of strategies and tactics after World War I, of an updated armed neutrality strategy. The most pressing need for the LVA was modern fighter aircraft and the IML proposed the creation of eight new fighter squadrons. Four of these squadrons were assigned to the role of air defense and IML required that two of the aforementioned squadrons be made up of high-performance, single-engine interceptors.

The first round of purchases according to the IML’s four-year-plan concentrated on building one bomber squadron, two jachtkruiser, or heavy fighter squadrons, and two interceptor squadrons. The British Hawker Hurricane Mk.I was considered as a contender as the single-engine interceptor for two Jachtvliegtuigafdeelingen (fighter squadrons), or JaVA, of the 1e Luchtvaartregiment, or 1 LvR. In September 1937, the Hurricane was just entering production when the LVA contacted Hawker about a potential order. Hawker offered an initial batch of up to 20 Hurricanes for delivery in late 1938. At the time, the Hurricane would have been the best interceptor available to the LVA and the LVA leadership was particularly impressed with the fighter’s rate of climb. The cost of the Hurricane was considered prohibitive at the time however, as the price of a Dutch Fokker D.XXI single-engine fighter was only 72% of that of the British fighter; this was a significant concern to the Ministry of Defense as the first round of purchases for the four-year-plan were already projected to be well over budget. Thus, the Hawker proposal was dropped and the Ministry of Defense ordered 36 Fokker D.XXIs on December 31, 1937 for 1 LvR’s two interceptor squadrons. With fixed-landing gear, mixed wood-steel tube-canvas construction, and a maximum speed of only 286mph, the D.XXI was hardly considered at the forefront of aviation technology however.

Hawker Hurricane Mk.I in hypothetical Militaire Luchtvaart camouflage and markings – Ryan K. Noppen collection


During its evaluations for the second round of purchases for the four-year-plan in the summer of 1938, the LVA decided to transfer its D.XXIs, then only entering production, to two fighter escort squadrons assigned to the Feldleger, or Field Army. Given the rapid pace of aviation technological development, the LVA decided it needed a something more on-the-cutting-edge for its interceptor squadrons. In conjunction with the IML, it created a new set of requirements for a single-engine interceptor: a maximum speed of 342mph, a time to service altitude (14,764ft) of five minutes, and a flight time of at least two hours. Accordingly, the IML again looked to the Hurricane as the interceptor for the LVA. A number of other nations had placed orders for Hurricanes by this time however and Hawker could not promise quick delivery to the LVA. Furthermore, the British Air Ministry instructed Hawker to prioritize export deliveries to nations which were likely to be inclined to ally with Great Britain in a potential general European conflict; the Netherlands was not considered as a likely ally and, as a result, any potential deliveries of Hurricanes to the LVA were likely to be delayed. While still interested in the Hurricane, the IML realized at the same time that the British had a new interceptor entering production which was superior to the Hurricane: the Supermarine Spitfire Mk.I. The IML made overtures to Supermarine about the Spitfire in late 1938/early 1939 but with increasing tensions on the Continent, the Air Ministry rigidly reserved all Spitfire production for the Royal Air Force.

Supermarine Spitfire Mk.I in hypothetical Militaire Luchtvaart camouflage and markings – Ryan K. Noppen Collection


The setbacks in orders for interceptors from Hawker and Supermarine did not overly concern the IML however as it believed it had found an interceptor superior to both the Hurricane and Spitfire. If the IML had been granted carte blanche with regard to fighter purchases, the Luftwaffe may have been met by a German fighter in the skies over the Netherlands in May 1940. In July 1938, the Heinkel firm had sent a prototype of its He 112B fighter for demonstration and testing at Schiphol. The German Reichsluftfahrtministerium or RLM allowed Heinkel to seek export customers for its He 112 design after the Messerschmitt Bf 109 had been selected as the Luftwaffe’s primary single-engine fighter. The He 112 V9 prototype demonstrated at Schiphol, powered by a 680hp Junkers Jumo 210D inline engine, had a maximum speed of only 301mph but this was considerably more than what Dutch fighter pilots were accustomed to; the pilots who tested the aircraft were greatly impressed. While the performance of this particular prototype was less than that of production model British Hawker Hurricanes and Supermarine Spitfires, Heinkel had dramatically increased the performance of another He 112 prototype with the installation of a 1,175hp Daimler-Benz DB 601Aa inline engine. This version of the He 112 had similar, if not better, performance to the Spitfire Mk.I, particularly with its similar elliptical wing, and the RLM decided that it would allow the export of the DB 601 engine to the Netherlands. Heinkel offered this higher-performance variant to the ML for purchase at the end of the demonstration at Schiphol. Ironically, if the LVA had purchased the DB 601Aa-powered He 112, it would have deployed a German-built fighter with superior performance than the Luftwaffe’s Bf 109s during the Meidagen. Unfortunately for the budget-conscious LVA, the DB 601Aa-powered He 112 (like most things German with engines) had a prohibitively steep purchase price.


DB 601Aa-powered Heinkel He 112B in hypothetical Militaire Luchtvaart camouflage and markings – Ryan K. Noppen Collection


Back in the Netherlands, the Fokker company realized that it had to take drastic action if it was to continue to receive fighter contracts from the LVA. For roughly 15 years the Dutch Ministry of Defense had compelled the Dutch air services to adhere to a “buy Dutch” acquisition policy, regardless of whether or not the aircraft were the most competitive on the market. This policy changed with the introduction of the four-year-plan in light of the increasing militarism on the Continent. Fokker’s immediate answer to the new challenge of foreign fighters was to increase the performance of the D.XXI design. During the summer of 1938, Fokker proposed two variants of the D.XXI to the IML, using the same airframe but with retractable landing gear: the Ontwerp (project) 150, powered by a Bristol Hercules radial engine, and the Ontwerp 151, powered by either a Daimler Benz DB 600H inline engine or a British Rolls Royce Merlin II inline engine. Neither variant had spectacular performance compared to new foreign developments, particularly the Spitfire and the Bf 109, so they never went beyond the drawing board.


Militaire Luchtvaart Fokker D.XXI – Ryan K. Noppen Collection


Undaunted, Fokker went back to the IML in the autumn of 1938 with a radical new design which appeared as an antithesis to the orthodox D.XXI design. Prepared by Fokker’s new chief designer Marius Beeling, Ontwerp, 155 was a single-seat fighter with two in-line engines placed in the fuselage in a tandem push-pull arrangement, with twin tail booms, and with an armament of six 7.9mm Browning machine guns. This fighter would be of all-metal construction and powered by two Walter-Sagitta 528hp air-cooled inline engines from the Czechoslovakian engine firm of Josef Walter in Prague. Maximum speed was projected to be 326mph and Fokker presented variants powered other engines, such as the Junkers Jumo 210Ga (745hp) and the Rolls Royce Kestrel IV (755hp) which would have further increased the fighter’s performance; the Jumo engine would have given the plane a top speed of 345mph (555km/h), and the Kestrel 351mph (565km/h), both of them close to the maximum speeds of the Spitfire and the Bf 109E. Fokker’s reason for the selection of the engines listed above was that they were readily available for export purchase. Fokker wanted to demonstrate to the IML that Ontwerp 155 could offer competitive performance with engines which were not only available but not as expensive as the most recent high-performance models (especially as two engines were required for the aircraft). Fokker hoped to later acquire Rolls Royce Merlin II or Daimler Benz DB 601Aa engines for Ontwerp 155 (likely bringing the aircraft’s maximum speed over 380mph), particularly the later after learning that the German RLM allowed for their eventual export to the Netherlands. The IML was very interested in Ontwerp 155, surprised at such a revolutionary design from Fokker, and encouraged the company to proceed with further development. This did not equate to a purchase order but Fokker went ahead with prototype development in the hopes of securing an ML contract. The prototype of the new Fokker D.XXIII first flew on May 30, 1939.

Fokker D.XXIII prototype in Militaire Luchtvaart 1940 markings and camouflage – Ryan K. Noppen Collection


The aviation department of the major Dutch shipyard of NV Koninklijke Maatschappij De Schelde, decided to submit its own fighter project to the IML for consideration in the summer of 1938. Earlier that year, De Schelde’s designer, Theo Slot, began work on the S.20, a four-person cabin plane with the 160-hp Hirth HM 506A air-cooled engine located behind the cockpit in a pusher arrangement with twin tail booms. It was a rather unusual engine configuration, but Slot believed that it held promise for a high-performance fighter. Slot then began designing the De Schelde S.21 single-seat fighter, which had an extensively glazed nose, twin tail booms, wings constructed in an inverted gull shape, and an in-line engine located behind the cockpit and firewall. Armament consisted of a Madsen 23mm cannon in the nose and four Browning 7.9mm machine guns, two located on each side of the cockpit alongside the pilot’s seat. The fully glazed nose would give the pilot exceptional visibility, and the aircraft’s small size allowed for less weight and an overall excellent performance. The original engine intended for the S.21 was the 1,050-hp Daimler-Benz DB.600Ga, more readily available than the DB 601Aa, which would produce a projected top speed of 367mph. By the summer of 1939, the S.21 prototype was beginning to take shape, and the IML was considerably impressed with this advanced design.

De Schelde S.21 in hypothetical Militaire Luchtvaart camouflage and markings – Ryan K. Noppen Collection


On October 22, 1938, the IML submitted a formal report to the Minister of Defense, Dr. Jannes van Dijk, which outlined its recommendations for the remaining purchases of the four-year-plan. For the remaining 36 single-engine interceptors, the IML recommended the immediate purchase of 18 Hurricane Mk.Is and to select either the Fokker D.XXIII or De Schelde S.21 for the remaining 18 fighters, pending the testing results of the respective prototypes. The IML further recommended that if the D.XXIII and S.21 both proved to be unsatisfactory, then the purchase of DB 601Aa-engined He 112s or Spitfire Mk.Is should be pursued. While this was the formal proposal, it can be extrapolated from the IML’s individual aircraft evaluations that the He 112 and the S.21 were the most-favored designs among the IML’s members.  Unfortunately, the He 112 had the highest price tag of the evaluated fighters and the S.21 was the least-developed design at the time. The reason for the immediate purchase of the Hurricanes was that it was the only fighter among the above listed that was in full production and that had a proven operational track record. Neither the D.XXIII or S.21 prototypes were completed, nor would they be until likely the later part of 1939. The difficulties in procuring the Spitfire were mentioned earlier while Heinkel had only fitted a DB 601Aa to an He 112 prototype; this variant had not yet entered series production. Thus, the IML made a conservative half-step in selecting 18 Hurricanes but was willing to gamble the acquisition of its remaining 18 interceptors yet-to-be produced, higher-performance fighters. Minister van Dijk did not respond to this report immediately and it was over half a year later that the LVA finally learned of his decision on the matter.    

On July 22, 1939, now-Generaal Best of the Wapen der Militaire Luchtvaart, or simply the Militaire Luchtvaart (ML) (the LVA was restructured as such on July 1, 1939) was briefed by Minister van Dijk that he had selected the Koolhoven FK 58 fighter as the ML’s new single-engine interceptor and had order 36 examples of the aircraft. Best and his officers were less-than-pleased with the selection as the performance of the FK 58 had been found lacking during previous LVA trials. The FK 58 was essentially an improved D.XXI with retractable landing gear and a more powerful engine and was originally designed as a cheap fighter at the request of the French Armée de l’Air; Erich Schatzki, the designer of the D.XXI, transferred to the N.V. Koolhoven firm in early 1938 following disagreements with Fokker. The French-contract FK 58 did not meet the LVA’s interceptor requirements; powered by a 1,030hp Gnome-Rhône 14N-16 radial engine, the FK 58 had a maximum speed of 295mph and had a slower rate-of-climb than the D.XXI. Best knew van Dijk was considering the FK 58 and the LVA commander wrote the Minister of Defense, specifically pointing out the aircraft’s failings. Frits Koolhoven however had privately consulted with van Dijk, promising the minister an upgraded variant of the FK 58, powered by a 1,080hp Bristol Taurus III radial engine which supposedly would give the fighter a maximum speed of 336mph. The primary appeal of the aircraft to van Dijk however was Koolhoven’s promise of the lowest price tag being offered for any of the interceptors under consideration.

Koolhoven FK 58 prototype in factory colors and markings, Spring 1940 – Ryan K. Noppen Collection


Van Dijk’s successor as Minister of Defense, Adriaan Dijxhoorn, was left to order the Taurus engines in September 1939 as a new Dutch government came to power in August of that year. Dijxhoorn was dismayed to learn that the British government refused the export of the engines due to the start of World War II. This left only 830hp Bristol Mercury VIII radials, still in Dutch stocks as they were used by both Fokker D.XXIs and G.1As, to power the yet-to-be-manufactured FK 58s. Dijxhoorn then cancelled the FK 58 order with Koolhoven as this would have resulted in a fighter totally unsuited for the interceptor role and with performance worse than the older D.XXI. Only a handful of FK 58s were delivered to the Armée de l’Air before the German invasion of the West in May 1940 as Koolhoven had grossly overestimated his factory’s ability to meet the delivery schedules he promised; given that, it is likely that no FK 58s, even if Koolhoven had obtained Taurus radials from Bristol, would have been delivered to the Dutch ML prior to May 1940. Minister Dijxhoorn was more sympathetic to the performance standards laid out by the IML than van Dijk had been but he arrived in office too late to get the ML the interceptors it needed. Bristol was not the only foreign manufacturer which had been denied export sales because of the war; almost all other major European aircraft companies had their production tied to the wartime needs of their respective nations. Dutch diplomatic efforts opened dialogue with both the British and German governments regarding the sale of fighters to the ML but nothing materialized by May 1940. In early 1940, several companies in the United States communicated that they were able to sell fighters to the ML but the German invasion occurred before a single American aircraft could be delivered. Lastly, only one prototype of the Fokker D.XXIII had flown by May 10, 1940 while the De Schelde S.21 prototype was still under construction.

The quest of the Dutch LVA/ML to obtain a high-performance interceptor in the late 1930s was a tortured one and did not bear any fruit prior to the German invasion. It is an interesting study however as it shows that the leadership of the LVA/ML clearly understood the importance of such an aircraft, made no small effort to obtain one, and demonstrated a modernizing imperative towards its air defense strategies. The D.XXIII and S.21 programs at Fokker and De Schelde also demonstrated that Dutch aircraft manufacturers rose to the challenge and were able to develop competitive designs which in some respects would have resulted in aircraft superior to their foreign counterparts. Unfortunately, time and politics were not on the side of the LVA/ML in this matter. It is unlikely that modern interceptors would have stemmed the tide of the Netherlands Campaign in May 1940 but they likely would have added to what was already an impressive kill ratio against the German Luftwaffe.