The Dornier Do 24 was a three engine flying boat developed in the interwar period by German manufacturer Dornier. Although developed in Germany, it was also constructed for the foreign market and built in the Netherlands and Switzerland to circumnavigate restrictions in place under the Treaty of Versailles.
Despite the industrial collaboration between the Dutch and Germans, the Netherlands fell to Nazi occupation in 1940 despite Dutch neutrality. The Do 24’s production resumed in occupied France and the Netherlands.
However, as Do 24 airframes had already been transported abroad prior to the invasion of the Netherlands, the flying boat had the unusual distinction of being a German produced aircraft that saw service in both Allied and Axis forces, with the free Dutch and Australian militaries using the Do 24 against Japan.
In the post-war era, the Do 24 continued to serve with air forces in different European nations until the 1960s.
The Do 24 was conceived by the German aircraft manufacturer Dornier Flugzeugwerke in the early 1930s, although the aircraft was originally designed in part to meet a specification in the Netherlands calling for an aircraft that could operate on land and sea.
The Dutch government were looking to replace their fleet of German made Dornier Wal flying boats that were used extensively by the Royal Netherlands Navy in the Dutch East Indies colony on transport and maritime patrol duties.
The Dutch specification call worked to the advantage of Dornier since Germany’s domestic aircraft manufacturing sector had limits imposed on it by the Treaty of Versailles. It mandated that planes built in Germany could not annually exceed a certain production limit and could not be faster or possess a longer range and size than any aircraft produced in the country during the First World War.
German aircraft manufacturers such as Dornier circumnavigated these restrictions by designing their planes within Germany and then manufacturing them in France or the Netherlands and testing flying boats on the Swiss side of Lake Constance.
The Dutch government officially signed a contract for the new flying boat in August 1936 and ordered six complete units for evaluation. The German government also requested two models for test evaluations as a competitor against the Blohm & Voss BV 138 prototype.
Production on the initial units began in 1936 with the manufacturing lines and fitting process divided between factories in Germany and the Netherlands.
The Do 24 generally followed a conventional flying boat design. The fuselage was designed as a hull that could land on water with sponsons added for stability. The wings were fitted high on the fuselage with the sponsons and floats fitted beneath.
Dornier fitted three engines to the aircraft in the center of the wing above the fuselage. The power plant consisted of three Bramo 323R-2 Fafnir radial air cooled engines which could develop up to 1,000 hp each and provide a projected top speed of 210 miles per hour. The maximum altitude of the flying boat was around 24,500 feet.
However, as the Dutch government requested that the planes use the same engines as their fleet of American built Martin 139 bombers, the Do 24s intended for Dutch service had their units switched to the American produced Wright R-1820-F52 Cyclone radial engines. In Germany the engines were also alternated with diesel powered Junkers Jumo 205C units.
Armament was also fitted to the Do 24, although the manufacturers passed it off as defensive rather than intended for attack purposes. These consisted of two MG 15 machine guns – one at the front and one in the tail section – and an MG 151 cannon mounted in a turret in the middle of the fuselage. The designers also allowed for up to 2,600 pounds worth of bombs to be carried under the wings.
The Do 24 was finished with an all metal construction, which was particularly useful in the tough conditions in Dutch territories in the Far East.
The first working Do 24 was assembled in Switzerland and completed its maiden flight on the 3rd of July, 1937 on the Swiss side of Lake Constance on behalf of the Dutch customers and was named the Do X.
The initial test results exceeded expectations. The Netherlands increased their order for 90 examples of the flying boat with the view that they would enter service by the early 1940s. Thirty of the Do 24 X airframes would be built by Dornier in Germany while the remainder would be constructed under licence in the Netherlands by Dutch aircraft manufacturer Aviolanda.
The Dutch built versions were known as the Do 24K.
Two airframes were sent to Germany and fitted with the Junkers engine. These were sent for an evaluation flight in January 1938 but were placed into storage after the Luftwaffe did not immediately place orders.
Despite the collaborative working deal on the aircraft and the Dutch government declaring themselves to be neutral., Nazi Germany launched an invasion of the Netherlands along with the other low countries in 1940 as part of their European offensive.
The Aviolanda production of the Do 24 was paused following the invasion with Luftwaffe chiefs debating what to do with the half-finished aircraft sitting in the factory. The Luftwaffe maritime branch were not interested in the flying boat, having already opted for the Blohm and Voss Bv 138 as an ocean reconnaissance and search and rescue craft.
However, the Luftwaffe’s Seenotdienst (Sea Rescue Service) wing who rescued downed airmen expressed an interest in the Do 24 to replace their existing fleet of older Heinkel He 59 biplanes.
The occupying German forces gave orders for the thirteen half-completed Do 24’s sitting on the Aviolanda production line already fitted with the Wright engines to be finished while the remaining models were to be completed with the BMW Bramo 323R-2 engine. Full scale production resumed in the Netherlands under German military supervision, with many finished examples being confiscated and flown to Germany by Nazi military officials for Luftwaffe use.
The Luftwaffe first deployed the Do 24 in combat during the Battle of Narvik in 1940 where they were mostly used as troop and equipment transporter. The confiscated units from the Netherlands were appropriated for service with the Luftwaffe in the Mediterranean and transported troops during the Nazi occupation of Crete. They were also used as communication and liaison aircraft to communicate with German forces behind Allied lines.
The Nazi government also opened a second manufacturing line in occupied France after taking control of the factory of CAMS, a French aerospace company who specialised in flying boats and seaplanes. This production was overseen by engineers from French aircraft maker SNCAN under German supervision. Around forty Do 24 units were produced in France during the German occupation and these wound up in both Luftwaffe and French service.
Due to the international and unusual circumstances behind its production, the Do 24 would become one of few aircraft that would serve on the frontline with both the Allied and German forces, being deployed in military operations against Axis powers in the Far East despite its German origins.
Prior to the invasion of the Netherlands, the Dutch Air Force had already flown a squadron of thirty seven Do 24 units to the Dutch East Indies, and these were put into service with the free Dutch forces. These were painted with new black and orange triangle roundels to avoid confusion with British and French aircraft.
On the 17th of December, 1941 a Dutch Dornier Do 24 attacked and sank the Japanese Imperial Navy destroyer Shinonome while it was escorting an invasion fleet to attack the colony of British Borneo.
Several of the Do 24s were destroyed when Japan then invaded the Dutch East Indies, with only six of surviving airframes evacuated to Australia. These were integrated into the Royal Australian Air Force in February 1942 where they served as transport aircraft for Allied forces in the Pacific.
The Do 24 also wound up in military service within neutral countries. In 1944, twelve of the Dutch-made Do 24 Ks were delivered to the Spanish military on the condition that they would be used to rescue downed airmen from both sides. In October 1944, a Luftwaffe Do 24 made an emergency landing in Sweden. It was impounded by local customs officers and then bought from Germany by the Swedish Air Force, who used it as a transport and research plane.
Following the defeat of the Nazis in 1945, the Do 24 continued to see post-war service with the countries who had purchased units or built them under licence.
France continued to build Do 24 units after liberation with 40 rolling off the after war production line at the CAMS plant. These remained in service with the French Navy in a search and rescue role until 1952.
The Spanish Do 24s were supplemented by models made in occupied France but not delivered in time to the Luftwaffe before the Allied liberation. These continued to fly until the late 1960s with the Spanish government returning one example to Lake Constance for public display. The last Do 24 reportedly left Spanish service in 1972.
A number of Do 24s were preserved for public display, with one fully intact example displayed Lake Boga Flying Boat Museum in Lake Boga, Australia which had been used as a private boat and aircraft after its military service.