The BLS Ae 4/4 II was procured between 1964 and 1983 as a universal locomotive with good mountain performance, enabling trains to be transported at higher speeds and replacing the locomotives from the early years. Due to the highly successful design of the BLS Ae 4/4, the world’s first high-performance locomotive without leading or trailing axles, BLS and SLM based the new development on this series. The first five units were initially approved for only 125 km/h and were accordingly designated as Ae 4/4 II 261–265. In 1969, after modifying the body support to coil springs and conducting extensive test runs, they were approved for Series R and the maximum speed was increased to 140 km/h. Since then, the locomotives have been designated as Re 4/4 161–165. The new Arnold models come in an elegant cardboard box with chrome lettering and metal accents to mark the 60th anniversary of the Re 4/4. The packaging includes a booklet on the history of this successful locomotive, along with a silver metal keychain in the shape of a BLS Re 4/4. The models themselves are delivered in analog versions with a Next-18 interface and with switchable cab lighting for digital operation. They cannot be retrofitted with sound. The sound versions are already equipped with sound and "decoder on board" from the factory. Only original recordings of the BLS Re 4/4 were used for the locomotive sounds. In addition to cab lighting, the sound versions also feature a so-called "powerbank," which bridges even longer power interruptions on the track for several seconds.