Development of nuclear merchant ships began in the 1950s but on the whole has not been commercially successful. The 22,000 tonne US-built NS Savannah, was commissioned in 1962 and decommissioned eight years later. The reactor used 4.2% and 4.6% enriched uranium. It was a technical success, but not economically viable. It had a 74 MWt reactor delivering 16.4 MW to the propeller, but the reactor was uprated to 80 MWt in 1964. The German-built 15,000 tonne Otto Hahn cargo ship and research facility sailed some 650,000 nautical miles on 126 voyages in 10 years without any technical problems. It had a 36 MWt reactor delivering 8 MW to the propeller. However, it proved too expensive to operate and in 1982 it was converted to diesel.