The Caterpillar D7 is a medium bulldozer manufactured by Caterpillar Inc.. The first D7 appeared in 1938. The D7C came next in 1955. The D7D came in 1959. The 160 hp D7E in 1961. The 180 hp D7F 1969.The 200 hp D7G in 1974.The 215 hp in 1986.The D7H was the first D7 to come with the exclusive elevated drive sprocket undercarriage.The D7R replaced the D7H in 1996 with the current D7R Series 2 replacing that.