The model series designation 405 was first used at the end of the 1950s, and from 1958-1961 several prototypes of the Unimog SH and Unimog T were produced on the basis of the 404.1 series. These did not enter series production. From 2000 the structure of the Unimog portfolio was completely revised. The new model series of off-road capable implement carriers was given the designation 405. This ultra-modern vehicle had a cab of fibre-reinforced plastic, and offered excellent visibility and comfort. The model designations were also changed with the introduction of the 405 series. The model designations (U300, U400, U500) now no longer gave an indication of the engine output. The compact U20 implement carrier presented in 2006 was also part of the 405 series. It was based on the U300 and came with a full forward control cab which was used in similar form by the Brazilian Mercedes-Benz plant for the Accelo truck.