In the context of the Second World War and with no access to European industry in order to acquire new locomotives, the Companhia dos Caminhos de Ferro Portugueses, Companhia dos Caminhos de Ferro do Estado and Companhia da Beira Alta ordered several units from the American Locomotive Company (ALCO). They arrived in Portugal on board cargo ships during 1945. They were assembled at the company's General Workshops in Santa-Apolónia and Barreiro. These locomotives were of typical American design, inspired by the North American “locomotives of war”, where the cowcatcher, riveted smokebox door and American pavilion featured. Taken as a whole, it did not match the size of the smaller tender it ran with. This reduction in length was the solution found in order to fit on existing turntables at various stations in Portugal and to respect weight limits on many bridges. They were characterised by the simplicity of construction, technology and operation, robustness and reliability. Due to their versatility, they were frequently seen on both freight and passenger trains. These locomotives were always utilised south of the River Douro, as due to their weight they could not cross the D. Maria bridge. They were based at Santa Apolónia, Entroncamento and Barreiro depots. They also frequented the Eastern Line to Torre das Vargens and were withdrawn in 1968.