While teaching at Clark University, Goddard made many tests with existing rockets in 1915-1916 to determine their efficiencies, which were found to be very low (2%). Redesigned rockets were then tested, using black and smokeless powders. Goddard managed to achieve a 16.7% efficiency with a DeLaval nozzle. By mid-summer 1915, improved nozzles were achieving efficiencies of 40% and jet velocities of 6730 ft/sec. References: 377 .