During the 1920s, many of the company's engines were used in yachts—a market that vanished during the Great Depression of the 1930s. At that time, his employer and patron, Will Irwin, owned a controlling interest in the Purity Stores supermarket chain, in California. Cummins convinced Irwin to install diesel engines in the fleet of trucks used to deliver food and staples to the stores. The diesel trucks were far better at managing the California mountains than the gasoline engines of that time, and were much more durable and economical to run. The success at Purity Stores attracted considerable attention, and the over-the-road diesel truck industry thus came into being. Thereafter, the growth of Cummins Engine came mainly from supplying high-speed, high-torque engines, which buyers specified for installation in semi-trailer tractors from most of the major manufacturers.