But most people are familiar with chain saws, like the one shown above. Imagine a longer, wider chain saw mounted on a vehicle with wheels or tracks underneath, like the Ditch Witch R300 shown below. That’s a chain trencher.
Wikimedia Commons has a category with 32 images of them. The accompanying text says:
“A chain trencher cuts with a digging chain that is driven around a rounded metal frame (formerly sometimes a rotating wheel at the end of a boom). This type of trencher can cut ground that is too hard to cut with a bucket-type excavator. The angle of the boom can be adjusted to control the depth of the cut. To cut a trench, the boom is held at a fixed angle while the machine creeps slowly. Chain trenchers are used for narrow to wide trenches, especially in rural areas. The excavated material can be removed by conveyor belt to either side of the trench.”
Here’s what that Trencor 1660 HDE looks like. I found a 2000 brochure from Trencor here. The engine is a 750 hp turbocharged Caterpillar V-12 with two 520 gallon fuel tanks. Crawler tracks underneath (from a Caterpillar D8 bulldozer) are 19-1/2 feet long, and the rear overhang is another 12-1/2 feet. It’s 13 feet wide, 12 feet high, and weighs over 107 tons.
And here is a brief YouTube video of one at work:
Images of a chain saw and a Ditch Witch R300 both came from Wikimedia Commons.