fighter to arrive too late to decisively impact Germany's position in World War II. Nonetheless, it will be remembered as the first use of jet engines in service. The Heinkel-Hirth aviation powerplant firm also tried to create a more powerful turbojet engine, the Heinkel HeS 011 of nearly 3,000 pounds of thrust at full power, very late in the war to improve the propulsion options available to new German military jet aircraft designs, and to improve the performance of existing designs. It used a unique "diagonal" compressor section that combined the features of both centrifugal and axial-flow compressor layouts for turbojet powerplants, but remained on the test bench, with only some nineteen examples ever produced. In the UK, their first axial-flow engine, the Metrovick F.2, ran in 1941 and was first flown in 1943. Although more powerful than the centrifugal designs at the time, the Ministry considered its complexity and unreliability a drawback in wartime. The work at Metrovick led to the Armstrong Siddeley Sapphire engine which would be built in the US as the J65. Post World War II Following the end of the war, the German jet aircraft and jet engines were extensively studied by the victorious allies and contributed to work on early Soviet (see Arkhip Lyulka) and US jet fighters. The legacy of the axial-flow engine is seen in the fact that practically all jet engines on fixed wing aircraft have had some inspiration from this design. Centrifugal-flow engines have improved since their introduction. With improvements in bearing technology the shaft speed of the engine was increased, greatly reducing the diameter of the centrifugal compressor. The short engine length remains an advantage of this design, particularly for use in helicopters where overall size is more important than frontal area. Also, as their engine components are more robust they are less liable to foreign object damage than axial-flow compressor engines. Although German designs were more advanced aerodynamically, the combination of simplicity and the lack of requisite rare metals for the necessary advanced metallurgy (such as tungsten, chromium and titanium) for high-stress components such as turbine blades and bearings, etc. meant that the later produced German engines had a short service life and had to be changed after 10–25 hours. British engines were also widely manufactured under license in the US (see Tizard Mission), and were sold to Soviet Russia who reverse engineered them with the Nene going