By the late 1930s, airframe construction methods had progressed to the point where airframes could be built to any required size, founded on the all-metal airframe design technologies pioneered by Hugo Junkers in 1915 and constantly improved upon for over two decades to follow – especially in Germany with aircraft like the Dornier Do X flying boat and the Junkers G 38 airliner, and the Soviet Union with the enormous Maksim Gorki, the largest aircraft built anywhere in the 1930s.