Which German aircraft did the Japanese D1A dive bomber derive from?

Aichi already had a partnership under way with Heinkel and in 1931 asked the German firm to develop a dive bomber. To meet the requirement, Aichi drew on its technical agreements with Ernst Heinkel Flugzeugwerke and arranged for an He 66 to be shipped to Japan, where the company made several modifications to it to meet the specific demands of the programme.

The work included redesigning and strengthening the landing gear to withstand carrier landings, adopting a locally produced radial engine, and adding a second seat right behind the pilot. A Townend ring was also added around the engine cylinders, along with a slight sweep to the wing and a modified rudder, and the tailskid was replaced by a fixed tailwheel.

The D1A was deployed in the Second Sino-Japanese War and was among the first aircraft to see action in the opening phase of the conflict. The D1A2 had a somewhat longer career than the initial version of the D1A and in 1937 became notorious around the world when the type was used to sink the American gunboat Panay on the Yangtze River on 12 December 1937. Several aircraft took part in that incident, in which the United States Navy gunboat and three oil tankers were sunk.