With the introduction of the Junkers Ju 86 bomber of 1934, Junkers abandoned the corrugated sheeting of his earlier designs. The basic layout was used in the four-engine Junkers Ju 89 heavy bomber, but this program ended with the death of Walther Wever, and his Ural bomber program along with him. Junkers then adapted the Ju 89 to passenger use, introducing the Junkers Ju 90, one of the first planes specifically designed for scheduled trans-Atlantic flights to the US. Developed in 1937, the aircraft suffered multiple setbacks with crashes of prototypes in 1937 and 1938. Further refinements enabled certification in 1939 and spurred South African Airways to make an initial order for two aircraft fitted with US-built Pratt & Whitney engines. Just as the aircraft was being readied for its first commercial flights, World War II began. With the outbreak of hostilities, all models were requisitioned by the Luftwaffe for military air-transport roles, and later, long-range maritime patrol.