The third-generation C/K was introduced for the 1973 model year. Designated the "Rounded Line" generation by General Motors, the C/K grew in size inside and out. While relatively straight-lined and boxy in appearance (leading to their "Square-body" nickname the Rounded Line trucks were the first generation of the C/K to be designed with the use of computers. Alongside the introduction of the four-door crew cab, the third generation C/K marked the introduction of a dual rear-wheel pickup truck ("Big Dooley"). For 1978, the C/K became the first American full-size pickup truck sold with a diesel engine. The Rounded Line generation is the longest-produced version of the C/K model line, produced for 18 model years.