respectively, closer in size to the older D6C and D6D. The D6M XL and D6M LGP versions with 140 hp weighed 33,200 and 36,400 lbs.All used the Cat 3306T 6 cylinder engine. The D6R replaced the D6H in 1996, and came in five models ranging from the 165HP D6R to the 175HP D6R XL and XR, and the 185 HP D6R XL (IG) and D6R LGP.This was the first D6 with Caterpillar's elevated drive sprocket undercarriage. The D6H was introduced in 1986 along with 3 other H-Series track-type tractors.In 1977 the D6D with a 140 hp engine was introduced, as well as the D6D SA version with 125 hp (drawbar) for agricultural use.In 1959 the D6 was replaced with the D6B after 60,000 D6 4R/5R and 8U/9U tractors had been built.The D6 4R/5R was replaced by the D6 8U & 9U series, fitted with the 6-cylinder D318 engine of 66 hp, in 1947.