Between the 1950s and 1970s, the U.S. Army and Navy pioneered portable nuclear reactors, known as the Army Nuclear Power Program, designed to deliver electricity and heat to remote military installations. These early microreactors were built in factories and shipped in components, with several operating at remote sites before the program was shut down in 1977 due to high costs and reliability issues. Notable historic portable include: PM-1 (Sundance, Wyoming): Powered an Air Force radar station from 1962 to 1968, generating 1 MWe. PM-2A (Camp Century, Greenland): A 10 MWt/1.56 MWe reactor installed in 1960 under the Arctic ice, it was notable for using prefabricated modules. PM-3A (McMurdo Sound, Antarctica): Operated from 1962 to 1972, providing electricity and heat for the naval station. MH-1A (Panama Canal Zone): The first floating nuclear power plant (1968–1977), mounted on a converted Liberty ship (Sturgis) to provide 10 MWe. ML-1 (Idaho): A small 0.3 MWe mobile power plant (1962–1966) using a closed-cycle gas turbine, designed to be transported by truck, rail, or air. SL-1 (Idaho): A 1961 accident involving a meltdown at this experimental reactor killed three operators, influencing later safety regulations. Now, in the mid 2020s the concept of micro reactors is being reconsidered.