Wright D-1, In-line 6 Engine

As the Wright Brothers naturally sought more powerful engines as their aircraft further developed, they turned to six-cylinder vertical engines around 1911. But later, after merging with another major manufacturer in 1916, the Wright-Martin Company produced Hispano-Suiza V-8 engines under license.

In 1920 Wright-Martin dissolved, with most becoming part of Mack Trucks, while the new Wright Aeronautical Corporation began developing original designs for aviation. These included a special six-cylinder vertical engine for airships which had characteristics of the Maybach dirigible engines used in German Zeppelins. In June 1921, the U.S. Navy placed an order for three of these engines known as the Model D-1. In March 1922, the D-1 completed a 50-hour endurance test. The engine was the largest of its type built up to that time, but never entered production.