A sapper requires an Expert Worker for creation.
Quoting from the Readme file for v 1.1:
- "Sappers now use half of their movement points to dig a tunnel. Thus, if you don't move your sapper at all, you will be able to dig two tunnel spaces per turn.
- "In addition, you can now press the "S" key to have all of your units skip their turns until the next sapper comes up. This is useful for those long sieges where no one is moving except for sappers. If one of your units is fired upon, the skipping will automatically stop; however, units which have already passed will not get their moves back."