Aichi Tokei Denki requested a design for a reconnaissance seaplane from
Heinkel to enter in an IJN competition. Heinkel built a single HD 56
prototype that was evaluated against the
Nakajima E4N and the
Kawanishi E5K. The Heinkel design was announced the winner in 1931, on the condition that Aichi would address some shortcomings, particularly a lack of range. Refined versions of the "losing" Nakajima and Kawanishi designs would eventually see production, with the Nakajima design being built in far greater numbers.
Modifications to the HD 56 by Aichi included reductions in length and span, the replacement of the prototype's
Wright Whirlwind with a locally-built
Hitachi Tempu, and numerous detail changes. Flight tests were carried out at
Nagoya in August 1931, and the type was accepted into service the following year. E3As were still in service aboard
Sendai class cruisers at the beginning of the
Second Sino-Japanese War.
1 X as second letter is for experimental aircraft or imported technology demonstrators not intended for service,
2 Hyphenated trailing letter (-J, -K, -L, -N or -S) denotes design modified for secondary role, 3 Possibly incorrect designation, but used in many sources