They work as unit but police is not a name of a unite. In army you have: pluton, szwadron, oddział, pułk, kompania (I've never been in army so excuse me if I use those terms wrongly) so whole range of smaller and bigger units which togheter make the biggest unit - army. That's how I understand it.
Ok, Strzyga's question from previous page now:
SINGULAR OR PLURAL
copied from the article thread
which one is better:
the initial sound in show and strength is not the same
the initial sounds in show and strength are not the same?
I bet on first sentence.