Ernst Heinkel Flugzeugwerke (Heinkel) of Germany began operations in the aviation business during December of 1922. From a Japanese Empire government request, their first single-seat, single-engine fighter became the "HD 23", a traditionally-arranged biplane intended for shipborne (catapult-launched, crane-recovered) operations. Following a first-flight in 1925-1926 and delivery of two prototypes from Germany in 1927, Aichi of Japan made some local modifications to the aircraft and built a further two more examples. Beyond these offerings, the GD 23 - known to the Japanese as the "Type H Carrier Fighter" - was not adopted for service after being evaluated at length by Imperial Japanese Navy (IJN) authorities.
As built, the HD 23 seated one pilot in an open-air cockpit positioned high over the nose section. The wing mainplanes were of equal span and included an upper and lower wing section joined by a network of support struts (N-style) and cabling. The lower fuselage incorporated a boat-like hull and held flotation bags for on-water landings in case of emergency. The undercarriage was wheeled at the two main leg members and fixed during flight. Dimensions included a length of 24.8 feet, a wingspan of 35.4 feet and a height of 12.4 feet. Empty weight was 3,240lb against an MTOW of 4,560lb.
The original German prototype (HD 23a) was powered by the BMW VIa 12-cylinder, water-cooled engine delivering 600 horsepower and the second followed with a Hispano-Suiza 12Ha engine of 450 horsepower. In-service aircraft were to carry 2 x 7.92mm machine guns synchronized to fire through the spinning propeller blades.
Once available to Aichi engineers in Japan, workers installed a jettisonable undercarriage for on-water operations (landing and take-off) as well as wing-based slats for better control. In testing the aircraft was found to possess poor qualities for a shipborne fighter - it was underpowered and heavy and exhibited inadequate control. In testing the HD 23a reached a speed of 160mph and a service ceiling of 26,000 feet.