Caterpillar D5
The Caterpillar D5 is a small track-type bulldozer manufactured by Caterpillar Inc. The original D5 series was only produced in 1939. The current D5 series being produced is the D5K. Versions. Over the years, Caterpillar often built different series of D5s at the same time, often with a lighter version having more in common with the smaller D3 and D4 tractors, and a larger version more akin to the much larger D6. Usually, the differentiation had to do with whether or not the machine incorporated an elevated or high sprocket drive. And later, this also determined the  type of transmission used, with the smaller series using a hydrostatic drive and the larger version typically having a Power-Shift transmission. These varying series have created some confusion with lineage, as the letter designation does not always correspond to when the model of machine was introduced. For example, the D5H came out years before the D5C. Interestingly, Caterpillar has now turned to a straight number designation (no letters) for all of its new track-laying tractors - starting, for the first time, with the D-1 and going all the way up to the D-11, with consistent size and weight breaks  between each model. This new designation has now put the current D5's weight at close to 43,000 pounds. This is a considerable increase over any previous D5 models. The heavier, elevated versions of these could weigh 34,000 lbs. at most, or as little as 20-25,000 lbs. for some of the lighter series, such as the D5C. Consequently the all-new D5 is much larger than any of the earlier versions.