Quote Originally Posted by Jambo
Here's a tricky one -

The can_sap ability in the export_descr_units text file, is only available to a selection of units. Some peasants can, some can't. Some infantry can, some can't. Some missile troops can, some can't.

Is it an oversight or meant to be?
It is meant to be that way.
Some cultures are not adept in the skills of engineering.
For example in original campaign, most of barbarain unit were unable to sap.