The D7 was first manufactured in 1938. A series of improved models were later produced, including the D7C in 1955, the D7D in 1959, the 160 hp D7E in 1961, the 180 hp D7F in 1969 and the 200 hp D7G in 1974. In 1986 the 215 hp D7H was the first D7 equipped with Caterpillar’s elevated drive sprocket undercarriage. The D7R replaced the D7H in 1996, followed by the D7R Series 2. The electric drive D7E entered service in early 2009, returning to a traditional ‘flat-track’ configuration for this iteration only. The high-drive design returned in 2020 with the introduction of the D7 (forgoing a generational letter under Caterpillar’s new naming system).