Before Cesarean sections if a baby was too large to pass through the birth canal, parts of the pelvis would be removed. At first, the procedure was performed with a small knife (without anesthesia) which was very messy and painful. In 1780, two doctors invented the chainsaw to make the removal both easier and less time-consuming. The original chainsaws were powered by a hand crank.
The chainsaw was soon used for other bone cutting operations and amputations in the surgical room. It then evolved into a woodworking tool when people noticed how quickly and easily it was to get through, well, anything. It became larger and more powerful and eventually grew to be the monster we know today.