The next new Unimog series emerged in 1974, two years after the MB-trac. Large-scale production began in 1975: the U 120 from the 425 series was the heavy-duty top model in the range of versatile tractors and working machines from Daimler-Benz. Its conspicuous features included a new, angular cab and a large bonnet set at a flat angle. The latter ended in a large-surfaced, black radiator grille. This cab design has basically remained unchanged for the last 25 years.
The 425 series initially included a 120 hp model (boosted shortly afterwards to 125 hp in the U 125) with 2810-millimetre wheelbase and a permitted gross vehicle weight of nine tonnes. Also in 1975, production of the 435 series as the successor to the Unimog S began for the German armed forces; these vehicles had wheelbase lengths of 3250, 3700 or even 3850 millimetres. From 1976, the 424 series was positioned lower in the range.