Heinkel He 59

The Heinkel He 59 was a twin-engined German biplane designed in 1930, resulting from a requirement for a torpedo bomber and reconnaissance aircraft able to operate on wheeled landing gear or twin-floats.
Development.
In 1930, Ernst Heinkel began developing an aircraft for the "Reichsmarine". To conceal the true military intentions, the aircraft was officially a civil aircraft. The He 59B landplane prototype was the first to fly, an event that took place in September 1931, but it was the He 59A floatplane prototype that paved the way for the He 59B initial production model, of which 142 were delivered in three variants. The Heinkel He 59 was a pleasant aircraft to fly; deficiencies noted were the weak engine, the limited range, the small load capability and insufficient armament.
Design.
The aircraft was of a mixed-material construction. The wings were made of a two-beam wooden frame, where the front was covered with plywood and the rest of the wing was covered with fabric. The box-shaped fuselage had a fabric-covered steel frame. The tail section was covered with lightweight metal sheets.
The keels of the floats were used as fuel tanks - each one holding 900 L (238 US gal) of fuel. Together with the internal fuel tank, the aircraft could hold a total of 2,700 L (713 US gal) of fuel. Two fuel tanks could also be placed in the bomb bay, bringing the total fuel capacity up to 3,200 L (845 US gal). The propeller was fixed-pitch with four blades.
Operations.
During the first months of World War II, the He 59 was used as a torpedo- and minelaying aircraft. Between 1940 and 1941 the aircraft was used as a reconnaissance aircraft, and in 1941-42 as a transport, air-sea rescue, and training aircraft. The trainer models survived slightly longer in service than operational models, but all had been retired or destroyed by 1944. Some aircraft were operated by the Condor Legion in Spain during the Spanish Civil War in 1936 as coastal reconnaissance and torpedo floatplanes.
The British claimed, as the air-sea rescue aircraft, despite carrying Red Cross markings, were being used for reconnaissance, they were legitimate targets. Even before then some had been forced down by British aircraft. One justification the British used resulted from the fact that in July 1940 they had shot down a white HE 59 near Deal, Kent that was clearly marked with red crosses simply because it was in the same air space as German fighters. Some have explained this violation by stating that the British were fearful that saboteurs might be landed using these aircraft, another claim was that a convoy passing through the heavily trafficked English channel had spotted a red cross marked HE 59 and was then attacked by bombers later in its voyage. When the crew of the HE 59 downed off Deal was captured the British noted that the pilot supposedly noted the position and direction of a British convoy in his log book. Using that pretext the British Air Ministry issued Bulletin 1254 indicating that all enemy air-sea rescue aircraft were to be destroyed wherever they were encountered. Later, Winston Churchill cast doubt on his own government's claims and motives when he wrote: "We did not recognize this means of rescuing enemy pilots who had been shot down in action, in order that they might come and bomb our civil population again." Germany protested the British attacks as rescue aircraft were part of the Geneva Convention agreement stipulating that belligerents must respect all "mobile sanitary formations" such as field ambulances and hospital ships. Churchill claimed that rescue aircraft were not anticipated by the treaty, and were therefore not covered. Because British attacks on He 59s continued the German Seenotdienst ordered the rescue aircraft armed and camouflaged. The use of civil registration and red cross markings was abandoned. A Seenotdienst gunner later shot down an attacking No. 43 Squadron RAF Hurricane fighter on July 20 Rescue flights were ordered to be protected by fighter aircraft whenever possible. 
The "Ilmavoimat" (Finnish Air Force) rented four aircraft from Germany in August 1943. These were used to ferry long-range reconnaissance patrols behind enemy lines. They were returned to Germany four months later.
References.
"Brandenburg Historica," The Luftwaffe Seenotdienst (Air Sea Rescue Service) of World War II