{| |} The Heinkel HD 56 was a reconnaissance seaplane developed in Germany in 1929 to operate from warships of the Imperial Japanese Navy, which designated it the Type 90-1 Reconnaissance Seaplane or E3A. It was a conventional single-bay biplane with staggered wings braced by N-type interplane struts. The pilot and gunner sat in tandem, open cockpits. Heinkel designed the aircraft at the request of Aichi, in order to submit it as their entry in an IJN competition to select such an aircraft. Heinkel built a single HD 56 prototype that was evaluated against the Nakajima Type 90-2 Reconnaissance Seaplane and the Kawanishi Type 90-3 Reconnaissance Seaplane. The Heinkel design announced the winner in 1931, on the condition that Aichi would address some shortcomings, particularly a lack of range