There are small units and each unit has its own clear mission. Each unit has only one mission. "Only one clear mission" is important and I need to emphasize it. I'd like to express the situation with a phrase and use it as a title of a presentation. I have made some candidate phrases. "Small units with a clear mission", "Small units with their own clear mission", "Small units with clear missions", etc. I think no one of them carries my intention properly. For example, "Small units with a clear mission" means that there is one mission and all units execute the mission. How can I express the situation with a phrase appropriately?
In think the inclusion of the word each would solve your problem. NOAD says in its definition for each:
each (adj. & pronoun) used to refer to every one of two or more people or things, regarded and identified separately
So, you could simply give your presentation this title:
Small Units – Each with a Clear Mission
As an aside, I prefer using a dash in the title. Dashes are used “to set off a word or phrase after an independent clause.” In this case, the dash offers a concise way to emphasize that each unit has a clear mission, while preventing the title from becoming overly wordy. You could used a colon, too (except colons are sometimes used to indicate a subtitle of a book, so that might make "Each with a Clear Mission" look more like a subtitle, as opposed to part of the title). A comma could work, also:
Small Units, Each with a Clear Mission
but I prefer the dash. Still, that’s a matter of preference.