"There are no bad regiments, only bad officers".
The most stupid can be trained to do a simple job and do it well, but they must be made to feel they are part of a team, that they are treated with a proper degree of respect, and that their work however "humble" is valued by their so-called leaders, who should also demonstrate an awareness that they share the same proportion of their DNA with the large primates.
And if that is not sufficient to produce best efforts, then there is always discipline.